Hello Charan, On Tue, 16 Jun 2020 at 19:13, Charan Teja Kalla <charante@xxxxxxxxxxxxxx> wrote: > > Thanks Sumit for the fix. > > On 6/11/2020 5:14 PM, Sumit Semwal wrote: > > Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which > > happens if the dma_buf_release() is called while the userspace is > > accessing the dma_buf pseudo fs's dmabuffs_dname() in another process, > > and dma_buf_release() releases the dmabuf object when the last reference > > to the struct file goes away. > > > > I discussed with Arnd Bergmann, and he suggested that rather than tying > > the dma_buf_release() to the file_operations' release(), we can tie it to > > the dentry_operations' d_release(), which will be called when the last ref > > to the dentry is removed. > > > > The path exercised by __fput() calls f_op->release() first, and then calls > > dput, which eventually calls d_op->d_release(). > > > > In the 'normal' case, when no userspace access is happening via dma_buf > > pseudo fs, there should be exactly one fd, file, dentry and inode, so > > closing the fd will kill of everything right away. > > > > In the presented case, the dentry's d_release() will be called only when > > the dentry's last ref is released. > > > > Therefore, lets move dma_buf_release() from fops->release() to > > d_ops->d_release() > > > > Many thanks to Arnd for his FS insights :) > > > > [1]: https://lore.kernel.org/patchwork/patch/1238278/ > > > > Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls") > > Reported-by: syzbot+3643a18836bce555bff6@xxxxxxxxxxxxxxxxxxxxxxxxx > > Cc: <stable@xxxxxxxxxxxxxxx> [5.3+] > > Cc: Arnd Bergmann <arnd@xxxxxxxx> > > Reported-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> > > Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx> > > Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx> > > > > Tested this patch for Android running on Snapdragon hardware and see no > issues. > Tested-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> Thanks for your tested-by, appreciate it! Chris, any luck with your CI to test if this also helps your dma_buf_release() bug that you guys have seen? If you've not been able to test, and there are no more objections by EOD today, I will merge this to the drm-misc-fixes branch. > > > --- > > v2: per Arnd: Moved dma_buf_release() above to avoid forward declaration; > > removed dentry_ops check. > > --- <snip> Best, Sumit.
