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

[Christian König]

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 at syzkaller.appspotmail.com
> Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
> Signed-off-by: Pavel Skripkin <paskripkin at 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 */