Am 01.04.22 um 23:31 schrieb 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
Well there are multiple issues with this patch. First of all as I wrote
before it shouldn't be possible that num_fences is zero.
We could still just add this as a precaution, but then bailing out is
the wrong thing to do here. Instead we should then make sure to allocate
at least one slot for a fence in the array.
But I think the cleanest would just be to not add a fence into the array
in the first place when num_fences is zero.
Regards,
Christian.
Fixes: 519f490db07e ("dma-buf/sync-file: fix warning about fence containers")
Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
---
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);
