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| Started by | Tyler Hicks <tyhicks@canonical.com> |
|---|---|
| First post | 2017-04-08 00:20 +0200 |
| Last post | 2017-04-08 01:50 +0200 |
| Articles | 3 — 2 participants |
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Re: [PATCH v3 0/4] Improved seccomp logging Tyler Hicks <tyhicks@canonical.com> - 2017-04-08 00:20 +0200
Re: [PATCH v3 0/4] Improved seccomp logging Kees Cook <keescook@chromium.org> - 2017-04-08 00:50 +0200
Re: [PATCH v3 0/4] Improved seccomp logging Tyler Hicks <tyhicks@canonical.com> - 2017-04-08 01:50 +0200
| From | Tyler Hicks <tyhicks@canonical.com> |
|---|---|
| Date | 2017-04-08 00:20 +0200 |
| Subject | Re: [PATCH v3 0/4] Improved seccomp logging |
| Message-ID | <ttKoy-5cY-13@gated-at.bofh.it> |
[Multipart message — attachments visible in raw view] — view raw
On 02/22/2017 12:46 PM, Kees Cook wrote:
> On Thu, Feb 16, 2017 at 3:29 PM, Kees Cook <keescook@chromium.org> wrote:
>> On Wed, Feb 15, 2017 at 7:24 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>> On Mon, Feb 13, 2017 at 7:45 PM, Tyler Hicks <tyhicks@canonical.com> wrote:
>>>> This patch set is the third revision of the following two previously
>>>> submitted patch sets:
>>>>
>>>> v1: http://lkml.kernel.org/r/1483375990-14948-1-git-send-email-tyhicks@canonical.com
>>>> v1: http://lkml.kernel.org/r/1483377999-15019-2-git-send-email-tyhicks@canonical.com
>>>>
>>>> v2: http://lkml.kernel.org/r/1486100262-32391-1-git-send-email-tyhicks@canonical.com
>>>>
>>>> The patch set aims to address some known deficiencies in seccomp's current
>>>> logging capabilities:
>>>>
>>>> 1. Inability to log all filter actions.
>>>> 2. Inability to selectively enable filtering; e.g. devs want noisy logging,
>>>> users want relative quiet.
>>>> 3. Consistent behavior with audit enabled and disabled.
>>>> 4. Inability to easily develop a filter due to the lack of a
>>>> permissive/complain mode.
>>>
>>> I think I dislike this, but I think my dislikes may be fixable with
>>> minor changes.
>>>
>>> What I dislike is that this mixes app-specific built-in configuration
>>> (seccomp) with global privileged stuff (audit). The result is a
>>> potentially difficult to use situation in which you need to modify an
>>> app to make it loggable (using RET_LOG) and then fiddle with
>>> privileged config (auditctl, etc) to actually see the logs.
>>
>> You make a good point about RET_LOG vs log_max_action. I think making
>> RET_LOG the default value would work for 99% of the cases.
>
> Actually, I take this back: making "log" the default means that
> everything else gets logged too, include "expected" return values like
> errno, trap, etc. I think that would be extremely noisy as a default
> (for upstream or Ubuntu).
>
> Perhaps RET_LOG should unconditionally log? Or maybe the logged
> actions should be a bit field instead of a single value? Then the
> default could be "RET_KILL and RET_LOG", but an admin could switch it
> to just RET_KILL, or even nothing at all? Hmmm...
Hi Kees - my apologies for going quiet on this topic after we spoke
about it more in IRC. I needed to tend to other work but now I'm able to
return to this seccomp logging patch set.
To summarize what we discussed in IRC, the Chrome browser makes
extensive use of RET_ERRNO, RET_TRACE, etc., to sandbox code that may
not ever be adjusted to keep from bump into the sandbox walls.
Therefore, it is unreasonable to enable logging of something like
RET_ERRNO on a system-wide level where Chrome browser is in use.
In contrast, snapd wants to set up "noisier" sandboxes for applications
to make it clear to the developers and the users that the sandboxed
application is bumping into the sandbox walls. Developers will know why
their code may not be working as intended and users will know that the
application is doing things that the platform doesn't agree with. These
sandboxes will end up using RET_ERRNO in the majority of cases.
This means that with the current design of this patch set, Chrome
browser will either be unintentionally spamming the logs or snapd's
sandboxes will be helplessly silent when both Chrome and snapd is
installed at the same time, depending on the admin's preferences.
To bring it back up a level, two applications may have a very different
outlook on how acceptable a given seccomp action is and they may
disagree on whether or not the user/administrator should be informed.
I've been giving thought to the idea of providing a way for the
application setting up the filter to opt into logging of certain
actions. Here's a high level breakdown:
- The administrator will have control of system-wide seccomp logging
and the application will have control of how its seccomp actions are
logged
- Both the administrator's and application's logging preferences are
bitmasks of actions that should be logged
- The default administrator bitmask is set to log all actions except
RET_ALLOW
+ Configurable via a sysctl
+ Very similar to the log_max_action syscall that was proposed in
this patch set but a bitmask instead of a max action
- The default application bitmask is set to log only RET_KILL and
RET_LOG
+ Configurable via the seccomp(2) syscall (details TBD)
- Actions are only logged when the application has requested the
action to be logged and the administrator has allowed the action to
be logged
+ By default, this is only RET_KILL and RET_LOG actions
Let me know what you think about this and I can turn out another patch
set next week if it sounds reasonable.
Tyler
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| From | Kees Cook <keescook@chromium.org> |
|---|---|
| Date | 2017-04-08 00:50 +0200 |
| Message-ID | <ttKRA-5mS-3@gated-at.bofh.it> |
| In reply to | #1619146 |
On Fri, Apr 7, 2017 at 3:16 PM, Tyler Hicks <tyhicks@canonical.com> wrote: > On 02/22/2017 12:46 PM, Kees Cook wrote: >> On Thu, Feb 16, 2017 at 3:29 PM, Kees Cook <keescook@chromium.org> wrote: >>> On Wed, Feb 15, 2017 at 7:24 PM, Andy Lutomirski <luto@amacapital.net> wrote: >>>> On Mon, Feb 13, 2017 at 7:45 PM, Tyler Hicks <tyhicks@canonical.com> wrote: >>>>> This patch set is the third revision of the following two previously >>>>> submitted patch sets: >>>>> >>>>> v1: http://lkml.kernel.org/r/1483375990-14948-1-git-send-email-tyhicks@canonical.com >>>>> v1: http://lkml.kernel.org/r/1483377999-15019-2-git-send-email-tyhicks@canonical.com >>>>> >>>>> v2: http://lkml.kernel.org/r/1486100262-32391-1-git-send-email-tyhicks@canonical.com >>>>> >>>>> The patch set aims to address some known deficiencies in seccomp's current >>>>> logging capabilities: >>>>> >>>>> 1. Inability to log all filter actions. >>>>> 2. Inability to selectively enable filtering; e.g. devs want noisy logging, >>>>> users want relative quiet. >>>>> 3. Consistent behavior with audit enabled and disabled. >>>>> 4. Inability to easily develop a filter due to the lack of a >>>>> permissive/complain mode. >>>> >>>> I think I dislike this, but I think my dislikes may be fixable with >>>> minor changes. >>>> >>>> What I dislike is that this mixes app-specific built-in configuration >>>> (seccomp) with global privileged stuff (audit). The result is a >>>> potentially difficult to use situation in which you need to modify an >>>> app to make it loggable (using RET_LOG) and then fiddle with >>>> privileged config (auditctl, etc) to actually see the logs. >>> >>> You make a good point about RET_LOG vs log_max_action. I think making >>> RET_LOG the default value would work for 99% of the cases. >> >> Actually, I take this back: making "log" the default means that >> everything else gets logged too, include "expected" return values like >> errno, trap, etc. I think that would be extremely noisy as a default >> (for upstream or Ubuntu). >> >> Perhaps RET_LOG should unconditionally log? Or maybe the logged >> actions should be a bit field instead of a single value? Then the >> default could be "RET_KILL and RET_LOG", but an admin could switch it >> to just RET_KILL, or even nothing at all? Hmmm... > > Hi Kees - my apologies for going quiet on this topic after we spoke > about it more in IRC. I needed to tend to other work but now I'm able to > return to this seccomp logging patch set. > > To summarize what we discussed in IRC, the Chrome browser makes > extensive use of RET_ERRNO, RET_TRACE, etc., to sandbox code that may > not ever be adjusted to keep from bump into the sandbox walls. > Therefore, it is unreasonable to enable logging of something like > RET_ERRNO on a system-wide level where Chrome browser is in use. > > In contrast, snapd wants to set up "noisier" sandboxes for applications > to make it clear to the developers and the users that the sandboxed > application is bumping into the sandbox walls. Developers will know why > their code may not be working as intended and users will know that the > application is doing things that the platform doesn't agree with. These > sandboxes will end up using RET_ERRNO in the majority of cases. > > This means that with the current design of this patch set, Chrome > browser will either be unintentionally spamming the logs or snapd's > sandboxes will be helplessly silent when both Chrome and snapd is > installed at the same time, depending on the admin's preferences. > > To bring it back up a level, two applications may have a very different > outlook on how acceptable a given seccomp action is and they may > disagree on whether or not the user/administrator should be informed. > > I've been giving thought to the idea of providing a way for the > application setting up the filter to opt into logging of certain > actions. Here's a high level breakdown: > > - The administrator will have control of system-wide seccomp logging > and the application will have control of how its seccomp actions are > logged > - Both the administrator's and application's logging preferences are > bitmasks of actions that should be logged > - The default administrator bitmask is set to log all actions except > RET_ALLOW > + Configurable via a sysctl > + Very similar to the log_max_action syscall that was proposed in > this patch set but a bitmask instead of a max action > - The default application bitmask is set to log only RET_KILL and > RET_LOG > + Configurable via the seccomp(2) syscall (details TBD) > - Actions are only logged when the application has requested the > action to be logged and the administrator has allowed the action to > be logged > + By default, this is only RET_KILL and RET_LOG actions > > Let me know what you think about this and I can turn out another patch > set next week if it sounds reasonable. This seems good to me. With a bitmask we don't have to play crazy games with levels, and with the app able to declare what it wants logged, we get the flexibility needed by app developers. One change I think I'd like to make is that an app can't block RET_KILL from being logged (the sysadmin can, though). What do think of that minor tweak? Is RET_ALLOW allowed to be logged by an application? I guess with it default-off for an admin, it should be okay. Does the app-controlled bitmask apply to the filter, the process, the process tree, or something else? e.g. systemd launches an app with a filter, leaving the defaults alone, then later process installs a filter and wants everything logged -- will things from the earlier filter get logged? -Kees -- Kees Cook Pixel Security
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| From | Tyler Hicks <tyhicks@canonical.com> |
|---|---|
| Date | 2017-04-08 01:50 +0200 |
| Message-ID | <ttLNE-61w-5@gated-at.bofh.it> |
| In reply to | #1619149 |
[Multipart message — attachments visible in raw view] — view raw
On 04/07/2017 05:46 PM, Kees Cook wrote:
> On Fri, Apr 7, 2017 at 3:16 PM, Tyler Hicks <tyhicks@canonical.com> wrote:
>> On 02/22/2017 12:46 PM, Kees Cook wrote:
>>> On Thu, Feb 16, 2017 at 3:29 PM, Kees Cook <keescook@chromium.org> wrote:
>>>> On Wed, Feb 15, 2017 at 7:24 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>>> On Mon, Feb 13, 2017 at 7:45 PM, Tyler Hicks <tyhicks@canonical.com> wrote:
>>>>>> This patch set is the third revision of the following two previously
>>>>>> submitted patch sets:
>>>>>>
>>>>>> v1: http://lkml.kernel.org/r/1483375990-14948-1-git-send-email-tyhicks@canonical.com
>>>>>> v1: http://lkml.kernel.org/r/1483377999-15019-2-git-send-email-tyhicks@canonical.com
>>>>>>
>>>>>> v2: http://lkml.kernel.org/r/1486100262-32391-1-git-send-email-tyhicks@canonical.com
>>>>>>
>>>>>> The patch set aims to address some known deficiencies in seccomp's current
>>>>>> logging capabilities:
>>>>>>
>>>>>> 1. Inability to log all filter actions.
>>>>>> 2. Inability to selectively enable filtering; e.g. devs want noisy logging,
>>>>>> users want relative quiet.
>>>>>> 3. Consistent behavior with audit enabled and disabled.
>>>>>> 4. Inability to easily develop a filter due to the lack of a
>>>>>> permissive/complain mode.
>>>>>
>>>>> I think I dislike this, but I think my dislikes may be fixable with
>>>>> minor changes.
>>>>>
>>>>> What I dislike is that this mixes app-specific built-in configuration
>>>>> (seccomp) with global privileged stuff (audit). The result is a
>>>>> potentially difficult to use situation in which you need to modify an
>>>>> app to make it loggable (using RET_LOG) and then fiddle with
>>>>> privileged config (auditctl, etc) to actually see the logs.
>>>>
>>>> You make a good point about RET_LOG vs log_max_action. I think making
>>>> RET_LOG the default value would work for 99% of the cases.
>>>
>>> Actually, I take this back: making "log" the default means that
>>> everything else gets logged too, include "expected" return values like
>>> errno, trap, etc. I think that would be extremely noisy as a default
>>> (for upstream or Ubuntu).
>>>
>>> Perhaps RET_LOG should unconditionally log? Or maybe the logged
>>> actions should be a bit field instead of a single value? Then the
>>> default could be "RET_KILL and RET_LOG", but an admin could switch it
>>> to just RET_KILL, or even nothing at all? Hmmm...
>>
>> Hi Kees - my apologies for going quiet on this topic after we spoke
>> about it more in IRC. I needed to tend to other work but now I'm able to
>> return to this seccomp logging patch set.
>>
>> To summarize what we discussed in IRC, the Chrome browser makes
>> extensive use of RET_ERRNO, RET_TRACE, etc., to sandbox code that may
>> not ever be adjusted to keep from bump into the sandbox walls.
>> Therefore, it is unreasonable to enable logging of something like
>> RET_ERRNO on a system-wide level where Chrome browser is in use.
>>
>> In contrast, snapd wants to set up "noisier" sandboxes for applications
>> to make it clear to the developers and the users that the sandboxed
>> application is bumping into the sandbox walls. Developers will know why
>> their code may not be working as intended and users will know that the
>> application is doing things that the platform doesn't agree with. These
>> sandboxes will end up using RET_ERRNO in the majority of cases.
>>
>> This means that with the current design of this patch set, Chrome
>> browser will either be unintentionally spamming the logs or snapd's
>> sandboxes will be helplessly silent when both Chrome and snapd is
>> installed at the same time, depending on the admin's preferences.
>>
>> To bring it back up a level, two applications may have a very different
>> outlook on how acceptable a given seccomp action is and they may
>> disagree on whether or not the user/administrator should be informed.
>>
>> I've been giving thought to the idea of providing a way for the
>> application setting up the filter to opt into logging of certain
>> actions. Here's a high level breakdown:
>>
>> - The administrator will have control of system-wide seccomp logging
>> and the application will have control of how its seccomp actions are
>> logged
>> - Both the administrator's and application's logging preferences are
>> bitmasks of actions that should be logged
>> - The default administrator bitmask is set to log all actions except
>> RET_ALLOW
>> + Configurable via a sysctl
>> + Very similar to the log_max_action syscall that was proposed in
>> this patch set but a bitmask instead of a max action
>> - The default application bitmask is set to log only RET_KILL and
>> RET_LOG
>> + Configurable via the seccomp(2) syscall (details TBD)
>> - Actions are only logged when the application has requested the
>> action to be logged and the administrator has allowed the action to
>> be logged
>> + By default, this is only RET_KILL and RET_LOG actions
>>
>> Let me know what you think about this and I can turn out another patch
>> set next week if it sounds reasonable.
>
> This seems good to me. With a bitmask we don't have to play crazy
> games with levels, and with the app able to declare what it wants
> logged, we get the flexibility needed by app developers.
>
> One change I think I'd like to make is that an app can't block
> RET_KILL from being logged (the sysadmin can, though). What do think
> of that minor tweak?
That's fine from my point of view.
>
> Is RET_ALLOW allowed to be logged by an application? I guess with it
> default-off for an admin, it should be okay.
As you say, it should be fine to allow but I don't know if there's any
real use in it. I can go either way here.
>
> Does the app-controlled bitmask apply to the filter, the process, the
> process tree, or something else? e.g. systemd launches an app with a
> filter, leaving the defaults alone, then later process installs a
> filter and wants everything logged -- will things from the earlier
> filter get logged?
I think implementation preferences may decide many of these questions.
As I see it, here are the options in order of my preference:
A) Claim the MSB of the filter return value and make the app logging
preference per-rule
- If the bit is set, log the rule
- Provides very fine-grained logging control at the "high cost" of
the remaining free bit in the filter return bitmask
- The bit can be ignored in the case of RET_KILL
- Can be synced across all threads in the calling task with the
SECCOMP_FILTER_FLAG_TSYNC filter flag
B) Claim a few bits in the filter flags and make the app logging
preference per-filter
- Something like SECCOMP_FILTER_FLAG_LOG_TRAP,
SECCOMP_FILTER_FLAG_LOG_ERRNO, and
SECCOMP_FILTER_FLAG_LOG_TRACE
- Logging for RET_KILL and RET_LOG can't be turned off
- I'd prefer not to waste a bit for RET_ALLOW in this case so it
simply won't be loggable
- Works with the SECCOMP_FILTER_FLAG_TSYNC filter flag
- Doesn't scale well if many new actions are added in the future
C) A simplified version of 'B' where only a single mode bit is claimed
to enable logging for all actions except RET_ALLOW
- Something like SECCOMP_FILTER_FLAG_LOG_ACTIONS
- Filters without this flag only log RET_KILL and RET_LOG
- Scales much better than 'B' at the expense of less flexibility
- Works with the SECCOMP_FILTER_FLAG_TSYNC filter flag
D) Claim a bit in the filter mode and make the app logging preference
per-process
- This new SECCOMP_MODE_ENABLE_LOGGING mode would take a bitmask of
actions that should be logged
- Incurs a small per-task increase in memory footprint in the form
of an additional member in 'struct seccomp'
- Has odd behavior you described above where launchers may set the
logging preference and then launched application may want
something different
I think 'A' is the cleanest design but I don't know if highly
configurable logging is deserving of the MSB bit in the filter return.
I'd like to hear your thoughts there.
I _barely_ prefer 'B' over 'C'. They're essential equal in my use case.
To be honest, I haven't completely wrapped my head around how 'D' would
actually work in practice so I may be writing it off prematurely.
Am I missing any more clever options that you can think of? Let me know
what you think of the possibilities.
Tyler
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