nilfs2: fix potential UAF of struct nilfs_sc_info in nilfs_segctor_thread()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix potential UAF of struct nilfs_sc_info in nilfs_segctor_thread() The finalization of nilfs_segctor_thread() can race with nilfs_segctor_kill_thread() which terminates that thread, potentially causing a use-after-free BUG as KASAN detected. At the end of nilfs_segctor_thread(), it assigns NULL to "sc_task" member of "struct nilfs_sc_info" to indicate the thread has finished, and then notifies nilfs_segctor_kill_thread() of this using waitqueue "sc_wait_task" on the struct nilfs_sc_info. However, here, immediately after the NULL assignment to "sc_task", it is possible that nilfs_segctor_kill_thread() will detect it and return to continue the deallocation, freeing the nilfs_sc_info structure before the thread does the notification. This fixes the issue by protecting the NULL assignment to "sc_task" and its notification, with spinlock "sc_state_lock" of the struct nilfs_sc_info. Since nilfs_segctor_kill_thread() does a final check to see if "sc_task" is NULL with "sc_state_lock" locked, this can eliminate the race.

References

• https://git.kernel.org/stable/c/034cce77d52ba013ce62b4f5258c29907eb1ada5
• https://git.kernel.org/stable/c/0dbf0e64b91ee8fcb278aea93eb06fc7d56ecbcc
• https://git.kernel.org/stable/c/613bf23c070d11c525268f2945aa594704a9b764
• https://git.kernel.org/stable/c/f32297dba338dc06d62286dedb3cdbd5175b1719
• https://git.kernel.org/stable/c/92684e02654c91a61a0b0561433b710bcece19fe
• https://git.kernel.org/stable/c/bae009a2f1b7c2011d2e92d8c84868d315c0b97e
• https://git.kernel.org/stable/c/b4d80bd6370b81a1725b6b8f7894802c23a14e9f
• https://git.kernel.org/stable/c/6be49d100c22ffea3287a4b19d7639d259888e33