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: <[email protected]>
Cc: Dave Hansen <[email protected]>
Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
Reported-by: Pawel Lebioda <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
---
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) {
dev_info(dev, "%s: %s: fail, attempted private mapping\n",
current->comm, func);
return -EINVAL;
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: <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
> Reported-by: Pawel Lebioda <[email protected]>
> Signed-off-by: Dan Williams <[email protected]>
> ---
> 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;
>
> --
On Mon, Dec 5, 2016 at 5:01 PM, Hugh Dickins <[email protected]> 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: <[email protected]>
>> Cc: Dave Hansen <[email protected]>
>> Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
>> Reported-by: Pawel Lebioda <[email protected]>
>> Signed-off-by: Dan Williams <[email protected]>
>> ---
>> 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...