CVE-2022-49995

In the Linux kernel, the following vulnerability has been resolved:

writeback: avoid use-after-free after removing device

When a disk is removed, bdi_unregister gets called to stop further writeback and wait for associated delayed work to complete. However, wb_inode_writeback_end() may schedule bandwidth estimation dwork after this has completed, which can result in the timer attempting to access the just freed bdi_writeback.

Fix this by checking if the bdi_writeback is alive, similar to when scheduling writeback work.

Since this requires wb->work_lock, and wb_inode_writeback_end() may get called from interrupt, switch wb->work_lock to an irqsafe lock.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/9a6c710f3bc10bc9cc23e1c080b53245b7f9d5b7
• https://git.kernel.org/stable/c/f87904c075515f3e1d8f4a7115869d3b914674fd
• https://git.kernel.org/stable/c/f96b9f7c1676923bce871e728bb49c0dfa5013cc