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

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Sep 18, 2020 at 01:16:16PM +0200, Christian König wrote:
> 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@vger.kernel.org> [5.7+]
> > Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
> 
> Reviewed-by: Christian König <christian.koenig@amd.com>
> 
> Going to pick this up for inclusion into drm-misc-next as well.

drm-misc-fixes since this is a bugfix that needs to be backported.
-Daniel

> 
> > ---
> >   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);
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch