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Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user

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  Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Vaishali Thakkar <vaishali.thakkar@oracle.com> - 2017-01-09 18:10 +0100
    Re: [Cocci] [PATCH] coccicheck: add a test for repeat  copy_from_user Julia Lawall <julia.lawall@lip6.fr> - 2017-01-09 20:20 +0100
      Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Kees Cook <keescook@chromium.org> - 2017-01-09 22:00 +0100
        Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Kees Cook <keescook@chromium.org> - 2017-01-09 23:10 +0100
    Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Vaishali Thakkar <vaishali.thakkar@oracle.com> - 2017-01-10 09:50 +0100
      Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Vaishali Thakkar <vaishali.thakkar@oracle.com> - 2017-01-10 18:50 +0100
        Re: [Cocci] [PATCH] coccicheck: add a test for repeat  copy_from_user Julia Lawall <julia.lawall@lip6.fr> - 2017-01-11 07:20 +0100
          Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Pengfei Wang <wpengfeinudt@gmail.com> - 2017-01-11 14:50 +0100
      Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Kees Cook <keescook@chromium.org> - 2017-01-10 20:20 +0100
    Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user Kees Cook <keescook@chromium.org> - 2017-01-10 20:20 +0100

#1554500 — Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user

On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
> I totally dropped the ball on this.  Many thanks to Vaishali for
> resurrecting it.
>
> Some changes are suggested below.
>
> On Tue, 26 Apr 2016, Kees Cook wrote:
>
>> This is usually a sign of a resized request. This adds a check for
>> potential races or confusions. The check isn't 100% accurate, so it
>> needs some manual review.
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>>  scripts/coccinelle/tests/reusercopy.cocci | 36 +++++++++++++++++++++++++++++++
>>  1 file changed, 36 insertions(+)
>>  create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
>>
>> diff --git a/scripts/coccinelle/tests/reusercopy.cocci b/scripts/coccinelle/tests/reusercopy.cocci
>> new file mode 100644
>> index 000000000000..53645de8ae95
>> --- /dev/null
>> +++ b/scripts/coccinelle/tests/reusercopy.cocci
>> @@ -0,0 +1,36 @@
>> +/// Recopying from the same user buffer frequently indicates a pattern of
>> +/// Reading a size header, allocating, and then re-reading an entire
>> +/// structure. If the structure's size is not re-validated, this can lead
>> +/// to structure or data size confusions.
>> +///
>> +// Confidence: Moderate
>> +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
>> +// URL: http://coccinelle.lip6.fr/
>> +// Comments:
>> +// Options: -no_includes -include_headers
>
> The options could be: --no-include --include-headers
>
> Actually, Coccinelle supports both, but it only officially supports the
> -- versions.
>
>> +
>> +virtual report
>> +virtual org
>
> Add, the following for the *s:
>
> virtual context
>
> Then add the following rule:
>
> @ok@
> position p;
> expression src,dest;
> @@
>
> copy_from_user@p(&dest, src, sizeof(dest))
>
>> +
>> +@cfu_twice@
>> +position p;
>
> Change this to:
>
> position p != ok.p;
>
>> +identifier src;
>> +expression dest1, dest2, size1, size2, offset;
>> +@@
>> +
>> +*copy_from_user(dest1, src, size1)
>> + ... when != src = offset
>> +     when != src += offset

Here, may be we should add few more lines from Pengfei's
script to avoid th potential FPs.

> Add the following lines:
>
>      when != if (size2 > e1 || ...) { ... return ...; }
>      when != if (size2 > e1 || ...) { ... size2 = e2 ... }
>
> These changes drop cases where the last argument to copy_from_usr is the
> size of the first argument, which seems safe enough, and where there is a
> test on the size value that can either update it or abort the function.
> These changes only eliminate false positives, as far as I could tell.
>
> If it would be more convenient, I could just send the complete revised
> patch, or whatever seems convenient.

I was also thinking that probably we should also add other user space 
memory API functions. May be get_user and strncpy_from_user. Although 
I'm not sure how common it is to find such patterns for both of these 
functions.

> thanks,
> julia
>
>> +*copy_from_user@p(dest2, src, size2)
>> +
>> +@script:python depends on org@
>> +p << cfu_twice.p;
>> +@@
>> +
>> +cocci.print_main("potentially dangerous second copy_from_user()",p)
>> +
>> +@script:python depends on report@
>> +p << cfu_twice.p;
>> +@@
>> +
>> +coccilib.report.print_report(p[0],"potentially dangerous second copy_from_user()")
>> --
>> 2.6.3
>>
>>
>> --
>> Kees Cook
>> Chrome OS & Brillo Security
>>
> _______________________________________________
> Cocci mailing list
> Cocci@systeme.lip6.fr
> https://systeme.lip6.fr/mailman/listinfo/cocci
>

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#1554620 — Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user

On Mon, 9 Jan 2017, Vaishali Thakkar wrote:

> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
> > I totally dropped the ball on this.  Many thanks to Vaishali for
> > resurrecting it.
> >
> > Some changes are suggested below.
> >
> > On Tue, 26 Apr 2016, Kees Cook wrote:
> >
> > > This is usually a sign of a resized request. This adds a check for
> > > potential races or confusions. The check isn't 100% accurate, so it
> > > needs some manual review.
> > >
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > ---
> > >  scripts/coccinelle/tests/reusercopy.cocci | 36
> > > +++++++++++++++++++++++++++++++
> > >  1 file changed, 36 insertions(+)
> > >  create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
> > >
> > > diff --git a/scripts/coccinelle/tests/reusercopy.cocci
> > > b/scripts/coccinelle/tests/reusercopy.cocci
> > > new file mode 100644
> > > index 000000000000..53645de8ae95
> > > --- /dev/null
> > > +++ b/scripts/coccinelle/tests/reusercopy.cocci
> > > @@ -0,0 +1,36 @@
> > > +/// Recopying from the same user buffer frequently indicates a pattern of
> > > +/// Reading a size header, allocating, and then re-reading an entire
> > > +/// structure. If the structure's size is not re-validated, this can lead
> > > +/// to structure or data size confusions.
> > > +///
> > > +// Confidence: Moderate
> > > +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
> > > +// URL: http://coccinelle.lip6.fr/
> > > +// Comments:
> > > +// Options: -no_includes -include_headers
> >
> > The options could be: --no-include --include-headers
> >
> > Actually, Coccinelle supports both, but it only officially supports the
> > -- versions.
> >
> > > +
> > > +virtual report
> > > +virtual org
> >
> > Add, the following for the *s:
> >
> > virtual context
> >
> > Then add the following rule:
> >
> > @ok@
> > position p;
> > expression src,dest;
> > @@
> >
> > copy_from_user@p(&dest, src, sizeof(dest))
> >
> > > +
> > > +@cfu_twice@
> > > +position p;
> >
> > Change this to:
> >
> > position p != ok.p;
> >
> > > +identifier src;
> > > +expression dest1, dest2, size1, size2, offset;
> > > +@@
> > > +
> > > +*copy_from_user(dest1, src, size1)
> > > + ... when != src = offset
> > > +     when != src += offset
>
> Here, may be we should add few more lines from Pengfei's
> script to avoid th potential FPs.

Which lines (I don't have it handy)?

julia

>
> > Add the following lines:
> >
> >      when != if (size2 > e1 || ...) { ... return ...; }
> >      when != if (size2 > e1 || ...) { ... size2 = e2 ... }
> >
> > These changes drop cases where the last argument to copy_from_usr is the
> > size of the first argument, which seems safe enough, and where there is a
> > test on the size value that can either update it or abort the function.
> > These changes only eliminate false positives, as far as I could tell.
> >
> > If it would be more convenient, I could just send the complete revised
> > patch, or whatever seems convenient.
>
> I was also thinking that probably we should also add other user space memory
> API functions. May be get_user and strncpy_from_user. Although I'm not sure
> how common it is to find such patterns for both of these functions.
>
> > thanks,
> > julia
> >
> > > +*copy_from_user@p(dest2, src, size2)
> > > +
> > > +@script:python depends on org@
> > > +p << cfu_twice.p;
> > > +@@
> > > +
> > > +cocci.print_main("potentially dangerous second copy_from_user()",p)
> > > +
> > > +@script:python depends on report@
> > > +p << cfu_twice.p;
> > > +@@
> > > +
> > > +coccilib.report.print_report(p[0],"potentially dangerous second
> > > copy_from_user()")
> > > --
> > > 2.6.3
> > >
> > >
> > > --
> > > Kees Cook
> > > Chrome OS & Brillo Security
> > >
> > _______________________________________________
> > Cocci mailing list
> > Cocci@systeme.lip6.fr
> > https://systeme.lip6.fr/mailman/listinfo/cocci
> >
>
>

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#1554714

On Mon, Jan 9, 2017 at 11:08 AM, Julia Lawall <julia.lawall@lip6.fr> wrote:
>
>
> On Mon, 9 Jan 2017, Vaishali Thakkar wrote:
>
>> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
>> > I totally dropped the ball on this.  Many thanks to Vaishali for
>> > resurrecting it.
>> >
>> > Some changes are suggested below.
>> >
>> > On Tue, 26 Apr 2016, Kees Cook wrote:
>> >
>> > > This is usually a sign of a resized request. This adds a check for
>> > > potential races or confusions. The check isn't 100% accurate, so it
>> > > needs some manual review.
>> > >
>> > > Signed-off-by: Kees Cook <keescook@chromium.org>
>> > > ---
>> > >  scripts/coccinelle/tests/reusercopy.cocci | 36
>> > > +++++++++++++++++++++++++++++++
>> > >  1 file changed, 36 insertions(+)
>> > >  create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
>> > >
>> > > diff --git a/scripts/coccinelle/tests/reusercopy.cocci
>> > > b/scripts/coccinelle/tests/reusercopy.cocci
>> > > new file mode 100644
>> > > index 000000000000..53645de8ae95
>> > > --- /dev/null
>> > > +++ b/scripts/coccinelle/tests/reusercopy.cocci
>> > > @@ -0,0 +1,36 @@
>> > > +/// Recopying from the same user buffer frequently indicates a pattern of
>> > > +/// Reading a size header, allocating, and then re-reading an entire
>> > > +/// structure. If the structure's size is not re-validated, this can lead
>> > > +/// to structure or data size confusions.
>> > > +///
>> > > +// Confidence: Moderate
>> > > +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
>> > > +// URL: http://coccinelle.lip6.fr/
>> > > +// Comments:
>> > > +// Options: -no_includes -include_headers
>> >
>> > The options could be: --no-include --include-headers
>> >
>> > Actually, Coccinelle supports both, but it only officially supports the
>> > -- versions.
>> >
>> > > +
>> > > +virtual report
>> > > +virtual org
>> >
>> > Add, the following for the *s:
>> >
>> > virtual context
>> >
>> > Then add the following rule:
>> >
>> > @ok@
>> > position p;
>> > expression src,dest;
>> > @@
>> >
>> > copy_from_user@p(&dest, src, sizeof(dest))
>> >
>> > > +
>> > > +@cfu_twice@
>> > > +position p;
>> >
>> > Change this to:
>> >
>> > position p != ok.p;
>> >
>> > > +identifier src;
>> > > +expression dest1, dest2, size1, size2, offset;
>> > > +@@
>> > > +
>> > > +*copy_from_user(dest1, src, size1)
>> > > + ... when != src = offset
>> > > +     when != src += offset
>>
>> Here, may be we should add few more lines from Pengfei's
>> script to avoid th potential FPs.
>
> Which lines (I don't have it handy)?

I'm going to compare
https://github.com/wpengfei/double_fetch_cocci/blob/master/pattern_match_linux.cocci
to my original one, add your improvements and see what I get...

-Kees

>
> julia
>
>>
>> > Add the following lines:
>> >
>> >      when != if (size2 > e1 || ...) { ... return ...; }
>> >      when != if (size2 > e1 || ...) { ... size2 = e2 ... }
>> >
>> > These changes drop cases where the last argument to copy_from_usr is the
>> > size of the first argument, which seems safe enough, and where there is a
>> > test on the size value that can either update it or abort the function.
>> > These changes only eliminate false positives, as far as I could tell.
>> >
>> > If it would be more convenient, I could just send the complete revised
>> > patch, or whatever seems convenient.
>>
>> I was also thinking that probably we should also add other user space memory
>> API functions. May be get_user and strncpy_from_user. Although I'm not sure
>> how common it is to find such patterns for both of these functions.
>>
>> > thanks,
>> > julia
>> >
>> > > +*copy_from_user@p(dest2, src, size2)
>> > > +
>> > > +@script:python depends on org@
>> > > +p << cfu_twice.p;
>> > > +@@
>> > > +
>> > > +cocci.print_main("potentially dangerous second copy_from_user()",p)
>> > > +
>> > > +@script:python depends on report@
>> > > +p << cfu_twice.p;
>> > > +@@
>> > > +
>> > > +coccilib.report.print_report(p[0],"potentially dangerous second
>> > > copy_from_user()")
>> > > --
>> > > 2.6.3
>> > >
>> > >
>> > > --
>> > > Kees Cook
>> > > Chrome OS & Brillo Security
>> > >
>> > _______________________________________________
>> > Cocci mailing list
>> > Cocci@systeme.lip6.fr
>> > https://systeme.lip6.fr/mailman/listinfo/cocci
>> >
>>
>>



-- 
Kees Cook
Nexus Security

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#1554744

On Mon, Jan 9, 2017 at 12:56 PM, Kees Cook <keescook@chromium.org> wrote:
> On Mon, Jan 9, 2017 at 11:08 AM, Julia Lawall <julia.lawall@lip6.fr> wrote:
>>
>> On Mon, 9 Jan 2017, Vaishali Thakkar wrote:
>>
>>> Here, may be we should add few more lines from Pengfei's
>>> script to avoid th potential FPs.
>>
>> Which lines (I don't have it handy)?
>
> I'm going to compare
> https://github.com/wpengfei/double_fetch_cocci/blob/master/pattern_match_linux.cocci
> to my original one, add your improvements and see what I get...

Okay, I finally had time to look at this. Pengfei added two other
logical cases that should be checked for, IIUC:

1) destination alias checking (with assignment either before or after
the first copy_from_user):

struct thing object;
struct thing *pointer = &object;

copy_from_user(..., &object);
...
copy_from_user(..., pointer);

2) field writes (via . or ->, instead of short writes):

struct thing object;

copy_from_user(..., &object.field);
...
copy_from_user(..., &object);


It'd probably better to convert Pengfei's into being able to run under
the coccicheck target.

-Kees

-- 
Kees Cook
Nexus Security

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#1555047

On Tuesday 10 January 2017 01:51 PM, Pengfei Wang wrote:
>
>> 在 2017年1月10日，上午1:05，Vaishali Thakkar <vaishali.thakkar@oracle.com> 写道：
>>
>> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
>>> I totally dropped the ball on this.  Many thanks to Vaishali for
>>> resurrecting it.
>>>
>>> Some changes are suggested below.
>>>
>>> On Tue, 26 Apr 2016, Kees Cook wrote:
>>>
>>>> This is usually a sign of a resized request. This adds a check for
>>>> potential races or confusions. The check isn't 100% accurate, so it
>>>> needs some manual review.
>>>>
>>>> Signed-off-by: Kees Cook <keescook@chromium.org>
>>>> ---
>>>> scripts/coccinelle/tests/reusercopy.cocci | 36 +++++++++++++++++++++++++++++++
>>>> 1 file changed, 36 insertions(+)
>>>> create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
>>>>
>>>> diff --git a/scripts/coccinelle/tests/reusercopy.cocci b/scripts/coccinelle/tests/reusercopy.cocci
>>>> new file mode 100644
>>>> index 000000000000..53645de8ae95
>>>> --- /dev/null
>>>> +++ b/scripts/coccinelle/tests/reusercopy.cocci
>>>> @@ -0,0 +1,36 @@
>>>> +/// Recopying from the same user buffer frequently indicates a pattern of
>>>> +/// Reading a size header, allocating, and then re-reading an entire
>>>> +/// structure. If the structure's size is not re-validated, this can lead
>>>> +/// to structure or data size confusions.
>>>> +///
>>>> +// Confidence: Moderate
>>>> +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
>>>> +// URL: http://coccinelle.lip6.fr/
>>>> +// Comments:
>>>> +// Options: -no_includes -include_headers
>>>
>>> The options could be: --no-include --include-headers
>>>
>>> Actually, Coccinelle supports both, but it only officially supports the
>>> -- versions.
>>>
>>>> +
>>>> +virtual report
>>>> +virtual org
>>>
>>> Add, the following for the *s:
>>>
>>> virtual context
>>>
>>> Then add the following rule:
>>>
>>> @ok@
>>> position p;
>>> expression src,dest;
>>> @@
>>>
>>> copy_from_user@p(&dest, src, sizeof(dest))
>>>
>>>> +
>>>> +@cfu_twice@
>>>> +position p;
>>>
>>> Change this to:
>>>
>>> position p != ok.p;
>>>
>>>> +identifier src;
>>>> +expression dest1, dest2, size1, size2, offset;
>>>> +@@
>>>> +
>>>> +*copy_from_user(dest1, src, size1)
>>>> + ... when != src = offset
>>>> +     when != src += offset
>>
>> Here, may be we should add few more lines from Pengfei's
>> script to avoid th potential FPs.
>>
>>> Add the following lines:
>>>
>>>     when != if (size2 > e1 || ...) { ... return ...; }
>>>     when != if (size2 > e1 || ...) { ... size2 = e2 ... }
>>>
>>> These changes drop cases where the last argument to copy_from_usr is the
>>> size of the first argument, which seems safe enough, and where there is a
>>> test on the size value that can either update it or abort the function.
>>> These changes only eliminate false positives, as far as I could tell.
>>>
>>> If it would be more convenient, I could just send the complete revised
>>> patch, or whatever seems convenient.
>>
>> I was also thinking that probably we should also add other user space memory API functions. May be get_user and strncpy_from_user. Although I'm not sure how common it is to find such patterns for both of these functions.
>
> I strongly recommend you adding get_user() API , which is used pervasively
> within the kernel just like copy_from user().

Sure. I have changed regetuser-wang.cocci from Kees's RFC patches to
include everything in the pattern matching rule. I'll send that as well.

> In many situations, there is a combination use, get_user() copies first then
> followed by a copy_from_user() copy. According to our investigation, this typical
> situation works by get_user() firstly copying a field of a specific struct to check,
> then copy_from_user() copies in the whole struct to use. Of course, the struct
> field is fetch twice.

Do you mean that there is a problem when we have get_user() followed by 
copy_from_user()? Basically something like
this:

get_user(..., src.arg) //where src.arg = field of a structure
...
copy_from_user(..., src, ...) //where src is a whole structure

If that is the case then we would need to have one more new script
or rule for such kind of combinational patterns. Disjunction can
probably give FPs.

Thanks!

> Regards
> Pengfei
>>
>>> thanks,
>>> julia
>>>
>>>> +*copy_from_user@p(dest2, src, size2)
>>>> +
>>>> +@script:python depends on org@
>>>> +p << cfu_twice.p;
>>>> +@@
>>>> +
>>>> +cocci.print_main("potentially dangerous second copy_from_user()",p)
>>>> +
>>>> +@script:python depends on report@
>>>> +p << cfu_twice.p;
>>>> +@@
>>>> +
>>>> +coccilib.report.print_report(p[0],"potentially dangerous second copy_from_user()")
>>>> --
>>>> 2.6.3
>>>>
>>>>
>>>> --
>>>> Kees Cook
>>>> Chrome OS & Brillo Security
>>>>
>>> _______________________________________________
>>> Cocci mailing list
>>> Cocci@systeme.lip6.fr <mailto:Cocci@systeme.lip6.fr>
>>> https://systeme.lip6.fr/mailman/listinfo/cocci <https://systeme.lip6.fr/mailman/listinfo/cocci>
>

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#1555772

On Tuesday 10 January 2017 02:32 PM, Pengfei Wang wrote:
>
>> 在 2017年1月10日，下午4:40，Vaishali Thakkar <vaishali.thakkar@oracle.com> 写道：
>>
>> On Tuesday 10 January 2017 01:51 PM, Pengfei Wang wrote:
>>>
>>>> 在 2017年1月10日，上午1:05，Vaishali Thakkar <vaishali.thakkar@oracle.com> 写道：
>>>>
>>>> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
>>>>> I totally dropped the ball on this.  Many thanks to Vaishali for
>>>>> resurrecting it.
>>>>>
>>>>> Some changes are suggested below.
>>>>>
>>>>> On Tue, 26 Apr 2016, Kees Cook wrote:
>>>>>
>>>>>> This is usually a sign of a resized request. This adds a check for
>>>>>> potential races or confusions. The check isn't 100% accurate, so it
>>>>>> needs some manual review.
>>>>>>
>>>>>> Signed-off-by: Kees Cook <keescook@chromium.org>
>>>>>> ---
>>>>>> scripts/coccinelle/tests/reusercopy.cocci | 36 +++++++++++++++++++++++++++++++
>>>>>> 1 file changed, 36 insertions(+)
>>>>>> create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
>>>>>>
>>>>>> diff --git a/scripts/coccinelle/tests/reusercopy.cocci b/scripts/coccinelle/tests/reusercopy.cocci
>>>>>> new file mode 100644
>>>>>> index 000000000000..53645de8ae95
>>>>>> --- /dev/null
>>>>>> +++ b/scripts/coccinelle/tests/reusercopy.cocci
>>>>>> @@ -0,0 +1,36 @@
>>>>>> +/// Recopying from the same user buffer frequently indicates a pattern of
>>>>>> +/// Reading a size header, allocating, and then re-reading an entire
>>>>>> +/// structure. If the structure's size is not re-validated, this can lead
>>>>>> +/// to structure or data size confusions.
>>>>>> +///
>>>>>> +// Confidence: Moderate
>>>>>> +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
>>>>>> +// URL: http://coccinelle.lip6.fr/
>>>>>> +// Comments:
>>>>>> +// Options: -no_includes -include_headers
>>>>>
>>>>> The options could be: --no-include --include-headers
>>>>>
>>>>> Actually, Coccinelle supports both, but it only officially supports the
>>>>> -- versions.
>>>>>
>>>>>> +
>>>>>> +virtual report
>>>>>> +virtual org
>>>>>
>>>>> Add, the following for the *s:
>>>>>
>>>>> virtual context
>>>>>
>>>>> Then add the following rule:
>>>>>
>>>>> @ok@
>>>>> position p;
>>>>> expression src,dest;
>>>>> @@
>>>>>
>>>>> copy_from_user@p(&dest, src, sizeof(dest))
>>>>>
>>>>>> +
>>>>>> +@cfu_twice@
>>>>>> +position p;
>>>>>
>>>>> Change this to:
>>>>>
>>>>> position p != ok.p;
>>>>>
>>>>>> +identifier src;
>>>>>> +expression dest1, dest2, size1, size2, offset;
>>>>>> +@@
>>>>>> +
>>>>>> +*copy_from_user(dest1, src, size1)
>>>>>> + ... when != src = offset
>>>>>> +     when != src += offset
>>>>
>>>> Here, may be we should add few more lines from Pengfei's
>>>> script to avoid th potential FPs.
>>>>
>>>>> Add the following lines:
>>>>>
>>>>>    when != if (size2 > e1 || ...) { ... return ...; }
>>>>>    when != if (size2 > e1 || ...) { ... size2 = e2 ... }
>>>>>
>>>>> These changes drop cases where the last argument to copy_from_usr is the
>>>>> size of the first argument, which seems safe enough, and where there is a
>>>>> test on the size value that can either update it or abort the function.
>>>>> These changes only eliminate false positives, as far as I could tell.
>>>>>
>>>>> If it would be more convenient, I could just send the complete revised
>>>>> patch, or whatever seems convenient.
>>>>
>>>> I was also thinking that probably we should also add other user space memory API functions. May be get_user and strncpy_from_user. Although I'm not sure how common it is to find such patterns for both of these functions.
>>>
>>> I strongly recommend you adding get_user() API , which is used pervasively
>>> within the kernel just like copy_from user().
>>
>> Sure. I have changed regetuser-wang.cocci from Kees's RFC patches to
>> include everything in the pattern matching rule. I'll send that as well.
>>
>>> In many situations, there is a combination use, get_user() copies first then
>>> followed by a copy_from_user() copy. According to our investigation, this typical
>>> situation works by get_user() firstly copying a field of a specific struct to check,
>>> then copy_from_user() copies in the whole struct to use. Of course, the struct
>>> field is fetch twice.
>>
>> Do you mean that there is a problem when we have get_user() followed by copy_from_user()? Basically something like
>> this:
>>
>> get_user(..., src.arg) //where src.arg = field of a structure
>> ...
>> copy_from_user(..., src, ...) //where src is a whole structure
>>
>> If that is the case then we would need to have one more new script
>> or rule for such kind of combinational patterns. Disjunction can
>> probably give FPs.
>
> Yes, I’ve seen these cases when examining the source code. Actually, copying a field
> first and then copying the whole struct is very common in the kernel especially the driver.
> For example, when a struct (or a message as we call it) is variable length, the first copy is
> used to check its size field, and allocate a kernel buffer based on it, then the second copy is
> to copy the whole message also based on the size. There are also situations of the
> variable type messages.
>
> The reason that they use get_user() instead of copy_from_user() for the first copy is because
> get_user() is defined as a macro, which works faster than a function call that copy_from_user() does
> when copy simple data type such as char and int.

I see. If possible, can you point me to a code or actual bug
[reported by you or others] which has this kind of pattern
particularly?

I wrote a separate rule for the kind of pattern you have
described but I am not sure if this kind of code is suspicious.
Like you said, it is very common to use this pattern in drivers.
So may be suspicious one can have a specific pattern for this
combinational usage of get_user and copy_from_user.

Thanks.

>
> Regards
> Pengfei
>
>
>> Thanks!
>>
>>> Regards
>>> Pengfei
>>>>
>>>>> thanks,
>>>>> julia
>>>>>
>>>>>> +*copy_from_user@p(dest2, src, size2)
>>>>>> +
>>>>>> +@script:python depends on org@
>>>>>> +p << cfu_twice.p;
>>>>>> +@@
>>>>>> +
>>>>>> +cocci.print_main("potentially dangerous second copy_from_user()",p)
>>>>>> +
>>>>>> +@script:python depends on report@
>>>>>> +p << cfu_twice.p;
>>>>>> +@@
>>>>>> +
>>>>>> +coccilib.report.print_report(p[0],"potentially dangerous second copy_from_user()")
>>>>>> --
>>>>>> 2.6.3
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Kees Cook
>>>>>> Chrome OS & Brillo Security
>>>>>>
>>>>> _______________________________________________
>>>>> Cocci mailing list
>>>>> Cocci@systeme.lip6.fr <mailto:Cocci@systeme.lip6.fr> <mailto:Cocci@systeme.lip6.fr <mailto:Cocci@systeme.lip6.fr>>
>>>>> https://systeme.lip6.fr/mailman/listinfo/cocci <https://systeme.lip6.fr/mailman/listinfo/cocci> <https://systeme.lip6.fr/mailman/listinfo/cocci <https://systeme.lip6.fr/mailman/listinfo/cocci>>
>
>

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#1556222 — Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user

I looked at the get_user part of the original script.  It looks like most
of the complexity is to deal with the possibility of the src location
being expressed in two different ways between the two calls.  Even if this
happens in practice only for get_user, it would seem that it could happen
for copy_from_user as well.  So I think we could just throw both get_user
and copy_from_user into the same rule?

I'm also not sure to understand why there are cases for things like

get_user(exp1, src->f1)
...
get_user(exp2,src)

Can this happen?  The types seem wrong.

Likewise, I see the need to take into account a second argument of src++,
but not the need to take into account a second argument of src+4.  Either
there is src+4 in both calls or the addresses involved are just different.

Perhaps I'm missing something, though.

julia

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#1556495

> 在 2017年1月11日，下午2:12，Julia Lawall <julia.lawall@lip6.fr> 写道：
> 
> I looked at the get_user part of the original script.  It looks like most
> of the complexity is to deal with the possibility of the src location
> being expressed in two different ways between the two calls.  

Yes, in addition to pointer alias and the “field-whole” double-fetch type 
as we mentioned previously, we also need to take into consideration of 
the explicit data type conversion of the src pointer, such as:
get_user(dst, src)
…
get_user(dst, (int*)src)

Also the embedded computation at the argument position, such as 
get_user(dst, ++src) , get_user(dst, align(src)), or get_user(dst, src[i]),
which could cause false positives. Loops also cause false positives.


> Even if this
> happens in practice only for get_user, it would seem that it could happen
> for copy_from_user as well.  So I think we could just throw both get_user
> and copy_from_user into the same rule?
> 
Agreed.

> I'm also not sure to understand why there are cases for things like
> 
> get_user(exp1, src->f1)
> ...
> get_user(exp2,src)
> 
> Can this happen?  The types seem wrong.
I think it is unreasonable. It doesn’t work in practice. It exists in my script 
because I combined different situations with disjunction but forgot to remove 
the infeasible ones. Please remove it. A practical one should be:
get_user(exp1, src->f1)
…
copy_from_user(exp2, src ,size)

> Likewise, I see the need to take into account a second argument of src++,
> but not the need to take into account a second argument of src+4.  Either
> there is src+4 in both calls or the addresses involved are just different.

src++ or src+4 are used when handling long messages byte by byte or word 
by word by means of a loop. I paid attention to these because they cause 
false positives as src pointers have changed for the double fetches. I remember 
both of these two situations when examining the source code but I cannot 
guarantee the src+4 situation exists as I don’t have an example in hand now. I suggest 
we focus on the src++ for now. If src+4 cause any false positives, we’ll add it, too.

Regards
Pengfei

> 
> Perhaps I'm missing something, though.
> 
> julia
> 

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#1555838

On Tue, Jan 10, 2017 at 12:40 AM, Vaishali Thakkar
<vaishali.thakkar@oracle.com> wrote:
> On Tuesday 10 January 2017 01:51 PM, Pengfei Wang wrote:
>>
>>
>>> 在 2017年1月10日，上午1:05，Vaishali Thakkar <vaishali.thakkar@oracle.com> 写道：
>>>
>>> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
>>>>
>>>> I totally dropped the ball on this.  Many thanks to Vaishali for
>>>> resurrecting it.
>>>>
>>>> Some changes are suggested below.
>>>>
>>>> On Tue, 26 Apr 2016, Kees Cook wrote:
>>>>
>>>>> This is usually a sign of a resized request. This adds a check for
>>>>> potential races or confusions. The check isn't 100% accurate, so it
>>>>> needs some manual review.
>>>>>
>>>>> Signed-off-by: Kees Cook <keescook@chromium.org>
>>>>> ---
>>>>> scripts/coccinelle/tests/reusercopy.cocci | 36
>>>>> +++++++++++++++++++++++++++++++
>>>>> 1 file changed, 36 insertions(+)
>>>>> create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
>>>>>
>>>>> diff --git a/scripts/coccinelle/tests/reusercopy.cocci
>>>>> b/scripts/coccinelle/tests/reusercopy.cocci
>>>>> new file mode 100644
>>>>> index 000000000000..53645de8ae95
>>>>> --- /dev/null
>>>>> +++ b/scripts/coccinelle/tests/reusercopy.cocci
>>>>> @@ -0,0 +1,36 @@
>>>>> +/// Recopying from the same user buffer frequently indicates a pattern
>>>>> of
>>>>> +/// Reading a size header, allocating, and then re-reading an entire
>>>>> +/// structure. If the structure's size is not re-validated, this can
>>>>> lead
>>>>> +/// to structure or data size confusions.
>>>>> +///
>>>>> +// Confidence: Moderate
>>>>> +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
>>>>> +// URL: http://coccinelle.lip6.fr/
>>>>> +// Comments:
>>>>> +// Options: -no_includes -include_headers
>>>>
>>>>
>>>> The options could be: --no-include --include-headers
>>>>
>>>> Actually, Coccinelle supports both, but it only officially supports the
>>>> -- versions.
>>>>
>>>>> +
>>>>> +virtual report
>>>>> +virtual org
>>>>
>>>>
>>>> Add, the following for the *s:
>>>>
>>>> virtual context
>>>>
>>>> Then add the following rule:
>>>>
>>>> @ok@
>>>> position p;
>>>> expression src,dest;
>>>> @@
>>>>
>>>> copy_from_user@p(&dest, src, sizeof(dest))
>>>>
>>>>> +
>>>>> +@cfu_twice@
>>>>> +position p;
>>>>
>>>>
>>>> Change this to:
>>>>
>>>> position p != ok.p;
>>>>
>>>>> +identifier src;
>>>>> +expression dest1, dest2, size1, size2, offset;
>>>>> +@@
>>>>> +
>>>>> +*copy_from_user(dest1, src, size1)
>>>>> + ... when != src = offset
>>>>> +     when != src += offset
>>>
>>>
>>> Here, may be we should add few more lines from Pengfei's
>>> script to avoid th potential FPs.
>>>
>>>> Add the following lines:
>>>>
>>>>     when != if (size2 > e1 || ...) { ... return ...; }
>>>>     when != if (size2 > e1 || ...) { ... size2 = e2 ... }
>>>>
>>>> These changes drop cases where the last argument to copy_from_usr is the
>>>> size of the first argument, which seems safe enough, and where there is
>>>> a
>>>> test on the size value that can either update it or abort the function.
>>>> These changes only eliminate false positives, as far as I could tell.
>>>>
>>>> If it would be more convenient, I could just send the complete revised
>>>> patch, or whatever seems convenient.
>>>
>>>
>>> I was also thinking that probably we should also add other user space
>>> memory API functions. May be get_user and strncpy_from_user. Although I'm
>>> not sure how common it is to find such patterns for both of these functions.
>>
>>
>> I strongly recommend you adding get_user() API , which is used pervasively
>> within the kernel just like copy_from user().
>
>
> Sure. I have changed regetuser-wang.cocci from Kees's RFC patches to
> include everything in the pattern matching rule. I'll send that as well.
>
>> In many situations, there is a combination use, get_user() copies first
>> then
>> followed by a copy_from_user() copy. According to our investigation, this
>> typical
>> situation works by get_user() firstly copying a field of a specific struct
>> to check,
>> then copy_from_user() copies in the whole struct to use. Of course, the
>> struct
>> field is fetch twice.
>
>
> Do you mean that there is a problem when we have get_user() followed by
> copy_from_user()? Basically something like
> this:
>
> get_user(..., src.arg) //where src.arg = field of a structure
> ...
> copy_from_user(..., src, ...) //where src is a whole structure
>
> If that is the case then we would need to have one more new script
> or rule for such kind of combinational patterns. Disjunction can
> probably give FPs.

Yup, we need a single script: I just split them into three for comparisons.

-Kees

-- 
Kees Cook
Nexus Security

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#1555837

On Tue, Jan 10, 2017 at 12:21 AM, Pengfei Wang <wpengfeinudt@gmail.com> wrote:
>
> 在 2017年1月10日，上午1:05，Vaishali Thakkar <vaishali.thakkar@oracle.com> 写道：
>
> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
>
> I totally dropped the ball on this.  Many thanks to Vaishali for
> resurrecting it.
>
> Some changes are suggested below.
>
> On Tue, 26 Apr 2016, Kees Cook wrote:
>
> This is usually a sign of a resized request. This adds a check for
> potential races or confusions. The check isn't 100% accurate, so it
> needs some manual review.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> scripts/coccinelle/tests/reusercopy.cocci | 36
> +++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
> create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
>
> diff --git a/scripts/coccinelle/tests/reusercopy.cocci
> b/scripts/coccinelle/tests/reusercopy.cocci
> new file mode 100644
> index 000000000000..53645de8ae95
> --- /dev/null
> +++ b/scripts/coccinelle/tests/reusercopy.cocci
> @@ -0,0 +1,36 @@
> +/// Recopying from the same user buffer frequently indicates a pattern of
> +/// Reading a size header, allocating, and then re-reading an entire
> +/// structure. If the structure's size is not re-validated, this can lead
> +/// to structure or data size confusions.
> +///
> +// Confidence: Moderate
> +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
> +// URL: http://coccinelle.lip6.fr/
> +// Comments:
> +// Options: -no_includes -include_headers
>
>
> The options could be: --no-include --include-headers
>
> Actually, Coccinelle supports both, but it only officially supports the
> -- versions.
>
> +
> +virtual report
> +virtual org
>
>
> Add, the following for the *s:
>
> virtual context
>
> Then add the following rule:
>
> @ok@
> position p;
> expression src,dest;
> @@
>
> copy_from_user@p(&dest, src, sizeof(dest))
>
> +
> +@cfu_twice@
> +position p;
>
>
> Change this to:
>
> position p != ok.p;
>
> +identifier src;
> +expression dest1, dest2, size1, size2, offset;
> +@@
> +
> +*copy_from_user(dest1, src, size1)
> + ... when != src = offset
> +     when != src += offset
>
>
> Here, may be we should add few more lines from Pengfei's
> script to avoid th potential FPs.
>
> Add the following lines:
>
>     when != if (size2 > e1 || ...) { ... return ...; }
>     when != if (size2 > e1 || ...) { ... size2 = e2 ... }
>
> These changes drop cases where the last argument to copy_from_usr is the
> size of the first argument, which seems safe enough, and where there is a
> test on the size value that can either update it or abort the function.
> These changes only eliminate false positives, as far as I could tell.
>
> If it would be more convenient, I could just send the complete revised
> patch, or whatever seems convenient.
>
>
> I was also thinking that probably we should also add other user space memory
> API functions. May be get_user and strncpy_from_user. Although I'm not sure
> how common it is to find such patterns for both of these functions.
>
>
> I strongly recommend you adding get_user() API , which is used pervasively
> within the kernel just like copy_from user().
>
> In many situations, there is a combination use, get_user() copies first then
> followed by a copy_from_user() copy. According to our investigation, this
> typical
> situation works by get_user() firstly copying a field of a specific struct
> to check,
> then copy_from_user() copies in the whole struct to use. Of course, the
> struct
> field is fetch twice.

For sure, yes. I just split it out initially so we could compare some
of the pieces the two scripts do. Getting the size check into the test
was important to reduce false positives, so I think we need to just
expand the rules a bit more to include the size checks.

-Kees

-- 
Kees Cook
Nexus Security

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