[PATCH] dmabuf: fix NULL pointer dereference in dma_buf_release()

[Christian König]

Am 18.09.20 um 12:32 schrieb Charan Teja Reddy:
> NULL pointer dereference is observed while exporting the dmabuf but
> failed to allocate the 'struct file' which results into the dropping of
> the allocated dentry corresponding to this file in the dmabuf fs, which
> is ending up in dma_buf_release() and accessing the uninitialzed
> dentry->d_fsdata.
>
> Call stack on 5.4 is below:
>   dma_buf_release+0x2c/0x254 drivers/dma-buf/dma-buf.c:88
>   __dentry_kill+0x294/0x31c fs/dcache.c:584
>   dentry_kill fs/dcache.c:673 [inline]
>   dput+0x250/0x380 fs/dcache.c:859
>   path_put+0x24/0x40 fs/namei.c:485
>   alloc_file_pseudo+0x1a4/0x200 fs/file_table.c:235
>   dma_buf_getfile drivers/dma-buf/dma-buf.c:473 [inline]
>   dma_buf_export+0x25c/0x3ec drivers/dma-buf/dma-buf.c:585
>
> Fix this by checking for the valid pointer in the dentry->d_fsdata.
>
> Fixes: 4ab59c3c638c ("dma-buf: Move dma_buf_release() from fops to dentry_ops")
> Cc: <stable at vger.kernel.org> [5.7+]
> Signed-off-by: Charan Teja Reddy <charante at codeaurora.org>

Reviewed-by: Christian König <christian.koenig at amd.com>

Going to pick this up for inclusion into drm-misc-next as well.

> ---
>   drivers/dma-buf/dma-buf.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 58564d82..844967f 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -59,6 +59,8 @@ static void dma_buf_release(struct dentry *dentry)
>   	struct dma_buf *dmabuf;
>   
>   	dmabuf = dentry->d_fsdata;
> +	if (unlikely(!dmabuf))
> +		return;
>   
>   	BUG_ON(dmabuf->vmapping_counter);
>