Hello Charan,
On Tue, 16 Jun 2020 at 19:13, Charan Teja Kalla charante@codeaurora.org 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 :)
Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls") Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com Cc: stable@vger.kernel.org [5.3+] Cc: Arnd Bergmann arnd@arndb.de Reported-by: Charan Teja Reddy charante@codeaurora.org Reviewed-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Sumit Semwal sumit.semwal@linaro.org
Tested this patch for Android running on Snapdragon hardware and see no issues. Tested-by: Charan Teja Reddy charante@codeaurora.org
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.