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Groups > linux.kernel > #1536578 > unrolled thread
| Started by | Hugh Dickins <hughd@google.com> |
|---|---|
| First post | 2016-12-06 02:10 +0100 |
| Last post | 2016-12-07 02:20 +0100 |
| Articles | 2 — 2 participants |
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Re: [PATCH] device-dax: fail all private mapping attempts Hugh Dickins <hughd@google.com> - 2016-12-06 02:10 +0100
Re: [PATCH] device-dax: fail all private mapping attempts Dan Williams <dan.j.williams@intel.com> - 2016-12-07 02:20 +0100
| From | Hugh Dickins <hughd@google.com> |
|---|---|
| Date | 2016-12-06 02:10 +0100 |
| Subject | Re: [PATCH] device-dax: fail all private mapping attempts |
| Message-ID | <sLcqB-3CS-15@gated-at.bofh.it> |
On Wed, 16 Nov 2016, Dan Williams wrote:
> The device-dax implementation originally tried to be tricky and allow
> private read-only mappings, but in the process allowed writable
> MAP_PRIVATE + MAP_NORESERVE mappings. For simplicity and predictability
> just fail all private mapping attempts since device-dax memory is
> statically allocated and will never support overcommit.
>
> Cc: <stable@vger.kernel.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
> Reported-by: Pawel Lebioda <pawel.lebioda@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> drivers/dax/dax.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
> index 0e499bfca41c..3d94ff20fdca 100644
> --- a/drivers/dax/dax.c
> +++ b/drivers/dax/dax.c
> @@ -270,8 +270,8 @@ static int check_vma(struct dax_dev *dax_dev, struct vm_area_struct *vma,
> if (!dax_dev->alive)
> return -ENXIO;
>
> - /* prevent private / writable mappings from being established */
> - if ((vma->vm_flags & (VM_NORESERVE|VM_SHARED|VM_WRITE)) == VM_WRITE) {
> + /* prevent private mappings from being established */
> + if ((vma->vm_flags & VM_SHARED) != VM_SHARED) {
I think that is more restrictive than you intended: haven't tried,
but I believe it rejects a PROT_READ, MAP_SHARED, O_RDONLY fd mmap,
leaving no way to mmap /dev/dax without write permission to it.
See line 1393 of mm/mmap.c: the test you want is probably
if (!(vma->vm_flags & VM_MAYSHARE))
Hugh
> dev_info(dev, "%s: %s: fail, attempted private mapping\n",
> current->comm, func);
> return -EINVAL;
>
> --
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| From | Dan Williams <dan.j.williams@intel.com> |
|---|---|
| Date | 2016-12-07 02:20 +0100 |
| Message-ID | <sLz3P-1f1-9@gated-at.bofh.it> |
| In reply to | #1536578 |
On Mon, Dec 5, 2016 at 5:01 PM, Hugh Dickins <hughd@google.com> wrote:
> On Wed, 16 Nov 2016, Dan Williams wrote:
>
>> The device-dax implementation originally tried to be tricky and allow
>> private read-only mappings, but in the process allowed writable
>> MAP_PRIVATE + MAP_NORESERVE mappings. For simplicity and predictability
>> just fail all private mapping attempts since device-dax memory is
>> statically allocated and will never support overcommit.
>>
>> Cc: <stable@vger.kernel.org>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
>> Reported-by: Pawel Lebioda <pawel.lebioda@intel.com>
>> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>> ---
>> drivers/dax/dax.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
>> index 0e499bfca41c..3d94ff20fdca 100644
>> --- a/drivers/dax/dax.c
>> +++ b/drivers/dax/dax.c
>> @@ -270,8 +270,8 @@ static int check_vma(struct dax_dev *dax_dev, struct vm_area_struct *vma,
>> if (!dax_dev->alive)
>> return -ENXIO;
>>
>> - /* prevent private / writable mappings from being established */
>> - if ((vma->vm_flags & (VM_NORESERVE|VM_SHARED|VM_WRITE)) == VM_WRITE) {
>> + /* prevent private mappings from being established */
>> + if ((vma->vm_flags & VM_SHARED) != VM_SHARED) {
>
> I think that is more restrictive than you intended: haven't tried,
> but I believe it rejects a PROT_READ, MAP_SHARED, O_RDONLY fd mmap,
> leaving no way to mmap /dev/dax without write permission to it.
>
> See line 1393 of mm/mmap.c: the test you want is probably
> if (!(vma->vm_flags & VM_MAYSHARE))
>
Yes, it is. Thank you!
Fix for the fix on the way...
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