[next] dma-buf/sync-file: do not allow zero size allocations

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: syzbot+5c943fe38e86d615cac2@syzkaller.appspotmail.com
Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 drivers/dma-buf/sync_file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

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: syzbot+5c943fe38e86d615cac2@syzkaller.appspotmail.com
> Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> ---
>   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