syzbot reported GPF in dma_fence_array_first(), which is caused by
dereferencing ZERO_PTR in dma-buf internals.
ZERO_PTR was generated in sync_file_merge(). This functuion tries to
reduce allocation size, but does not check if it reducing to 0.
Fix reported bug by validating `index` value before passing it to
krealloc_array().
Fail log:
general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 PID: 3595 Comm: syz-executor814 Not tainted 5.17.0-next-20220328-syzkaller #0
...
RIP: 0010:dma_fence_array_first+0x78/0xb0 drivers/dma-buf/dma-fence-array.c:234
...
Call Trace:
<TASK>
__dma_fence_unwrap_array include/linux/dma-fence-unwrap.h:42 [inline]
dma_fence_unwrap_first include/linux/dma-fence-unwrap.h:57 [inline]
sync_file_ioctl_fence_info drivers/dma-buf/sync_file.c:414 [inline]
sync_file_ioctl+0x248/0x22c0 drivers/dma-buf/sync_file.c:477
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
There was same problem with initial kcalloc() allocation in same
function, so it's fixed as well.
Reported-and-tested-by: [email protected]
Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
Signed-off-by: Pavel Skripkin <[email protected]>
---
drivers/dma-buf/sync_file.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index b8dea4ec123b..aa744f017008 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
++num_fences;
- if (num_fences > INT_MAX)
+ if (num_fences > INT_MAX || !num_fences)
goto err_free_sync_file;
fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
@@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
if (index == 0)
add_fence(fences, &index, dma_fence_get_stub());
- if (num_fences > index) {
+ if (index && num_fences > index) {
struct dma_fence **tmp;
/* Keep going even when reducing the size failed */
--
2.35.1
That problem is already fixed with patch 21d139d73f77 dma-buf/sync-file:
fix logic error in new fence merge code.
Am 30.03.22 um 00:14 schrieb Pavel Skripkin:
> syzbot reported GPF in dma_fence_array_first(), which is caused by
> dereferencing ZERO_PTR in dma-buf internals.
>
> ZERO_PTR was generated in sync_file_merge(). This functuion tries to
> reduce allocation size, but does not check if it reducing to 0.
This is actually perfectly ok. The code above should have prevented the
size to become 0.
Regards,
Christian.
>
> Fix reported bug by validating `index` value before passing it to
> krealloc_array().
>
> Fail log:
>
> general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
> CPU: 1 PID: 3595 Comm: syz-executor814 Not tainted 5.17.0-next-20220328-syzkaller #0
> ...
> RIP: 0010:dma_fence_array_first+0x78/0xb0 drivers/dma-buf/dma-fence-array.c:234
> ...
> Call Trace:
> <TASK>
> __dma_fence_unwrap_array include/linux/dma-fence-unwrap.h:42 [inline]
> dma_fence_unwrap_first include/linux/dma-fence-unwrap.h:57 [inline]
> sync_file_ioctl_fence_info drivers/dma-buf/sync_file.c:414 [inline]
> sync_file_ioctl+0x248/0x22c0 drivers/dma-buf/sync_file.c:477
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:870 [inline]
>
> There was same problem with initial kcalloc() allocation in same
> function, so it's fixed as well.
>
> Reported-and-tested-by: [email protected]
> Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
> Signed-off-by: Pavel Skripkin <[email protected]>
> ---
> drivers/dma-buf/sync_file.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index b8dea4ec123b..aa744f017008 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
> dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
> ++num_fences;
>
> - if (num_fences > INT_MAX)
> + if (num_fences > INT_MAX || !num_fences)
> goto err_free_sync_file;
>
> fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
> @@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
> if (index == 0)
> add_fence(fences, &index, dma_fence_get_stub());
>
> - if (num_fences > index) {
> + if (index && num_fences > index) {
> struct dma_fence **tmp;
>
> /* Keep going even when reducing the size failed */
Hi Christian,
On 3/30/22 10:09, Christian König wrote:
> That problem is already fixed with patch 21d139d73f77 dma-buf/sync-file:
> fix logic error in new fence merge code.
>
> Am 30.03.22 um 00:14 schrieb Pavel Skripkin:
>> syzbot reported GPF in dma_fence_array_first(), which is caused by
>> dereferencing ZERO_PTR in dma-buf internals.
>>
>> ZERO_PTR was generated in sync_file_merge(). This functuion tries to
>> reduce allocation size, but does not check if it reducing to 0.
>
> This is actually perfectly ok. The code above should have prevented the
> size to become 0.
>
> Regards,
> Christian.
>
Thanks for your reply! I see that 21d139d73f77 fixes GPF in
dma_fence_array_first(), but what about this part:
>>
>> - if (num_fences > INT_MAX)
>> + if (num_fences > INT_MAX || !num_fences)
>> goto err_free_sync_file;
>>
>> fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
>> @@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>> if (index == 0)
If num_fences is equal to zero then fences dereference will cause an
oops. Or this one is also fixed in your tree?
Thanks!
With regards,
Pavel Skripkin
Am 30.03.22 um 20:24 schrieb Pavel Skripkin:
> Hi Christian,
>
> On 3/30/22 10:09, Christian König wrote:
>> That problem is already fixed with patch 21d139d73f77 dma-buf/sync-file:
>> fix logic error in new fence merge code.
>>
>> Am 30.03.22 um 00:14 schrieb Pavel Skripkin:
>>> syzbot reported GPF in dma_fence_array_first(), which is caused by
>>> dereferencing ZERO_PTR in dma-buf internals.
>>>
>>> ZERO_PTR was generated in sync_file_merge(). This functuion tries to
>>> reduce allocation size, but does not check if it reducing to 0.
>>
>> This is actually perfectly ok. The code above should have prevented the
>> size to become 0.
>>
>> Regards,
>> Christian.
>>
>
> Thanks for your reply! I see that 21d139d73f77 fixes GPF in
> dma_fence_array_first(), but what about this part:
>
>>> - if (num_fences > INT_MAX)
>>> + if (num_fences > INT_MAX || !num_fences)
>>> goto err_free_sync_file;
>>> fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
>>> @@ -264,7 +264,7 @@ static struct sync_file *sync_file_merge(const
>>> char *name, struct sync_file *a,
>>> if (index == 0)
>
> If num_fences is equal to zero then fences dereference will cause an
> oops. Or this one is also fixed in your tree?
Well it is illegal for sync_file->fence to be NULL or we would run into
NULL pointer dereference much more often, so num_fences can't be zero
here either.
Regards,
Christian.
>
>
> Thanks!
>
>
>
>
> With regards,
> Pavel Skripkin
num_fences is user-controlled value and it can be equal to 0. Code
should not pass 0 to kcalloc(), since it will cause kcalloc() to return
ZERO_PTR. ZERO_PTR will pass `!fences` check and kernel will panic
because of dereferencing ZERO_PTR in add_fence()
Fix it by validating num_fences and bail out early if it is equal to 0
Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
Signed-off-by: Pavel Skripkin <[email protected]>
---
Changes since v1:
- Dropped already merged part
- Removed syzkaller's tag
---
drivers/dma-buf/sync_file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index b8dea4ec123b..024f22193e0c 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -212,7 +212,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
dma_fence_unwrap_for_each(b_fence, &b_iter, b->fence)
++num_fences;
- if (num_fences > INT_MAX)
+ if (num_fences > INT_MAX || !num_fences)
goto err_free_sync_file;
fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
--
2.35.1