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(-)
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 */