CVE-2023-53311

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

nilfs2: fix use-after-free of nilfs_root in dirtying inodes via iput

During unmount process of nilfs2, nothing holds nilfs_root structure after nilfs2 detaches its writer in nilfs_detach_log_writer(). Previously, nilfs_evict_inode() could cause use-after-free read for nilfs_root if inodes are left in garbage_list and released by nilfs_dispose_list at the end of nilfs_detach_log_writer(), and this bug was fixed by commit 9b5a04ac3ad9 (nilfs2: fix use-after-free bug of nilfs_root in nilfs_evict_inode()).

However, it turned out that there is another possibility of UAF in the call path where mark_inode_dirty_sync() is called from iput():

nilfs_detach_log_writer() nilfs_dispose_list() iput() mark_inode_dirty_sync() __mark_inode_dirty() nilfs_dirty_inode() __nilfs_mark_inode_dirty() nilfs_load_inode_block() –> causes UAF of nilfs_root struct

This can happen after commit 0ae45f63d4ef (vfs: add support for a lazytime mount option), which changed iput() to call mark_inode_dirty_sync() on its final reference if i_state has I_DIRTY_TIME flag and i_nlink is non-zero.

This issue appears after commit 28a65b49eb53 (nilfs2: do not write dirty data after degenerating to read-only) when using the syzbot reproducer, but the issue has potentially existed before.

Fix this issue by adding a purging flag to the nilfs structure, setting that flag while disposing the garbage_list and checking it in __nilfs_mark_inode_dirty().

Unlike commit 9b5a04ac3ad9 (nilfs2: fix use-after-free bug of nilfs_root in nilfs_evict_inode()), this patch does not rely on ns_writer to determine whether to skip operations, so as not to break recovery on mount. The nilfs_salvage_orphan_logs routine dirties the buffer of salvaged data before attaching the log writer, so changing __nilfs_mark_inode_dirty() to skip the operation when ns_writer is NULL will cause recovery write to fail. The purpose of using the cleanup-only flag is to allow for narrowing of such conditions.

Affected Software

References

• https://git.kernel.org/stable/c/11afd67f1b3c28eb216e50a3ca8dbcb69bb71793
• https://git.kernel.org/stable/c/3645510cf926e6af2f4d44899370d7e5331c93bd
• https://git.kernel.org/stable/c/37207240872456fbab44a110bde6640445233963
• https://git.kernel.org/stable/c/5828d5f5dc877dcfdd7b23102e978e2ecfd86d82
• https://git.kernel.org/stable/c/7532ff6edbf5242376b24a95a2fefb59bb653e5a
• https://git.kernel.org/stable/c/a3c3b4cbf9b8554120fb230e6516e980c6277487
• https://git.kernel.org/stable/c/d2c539c216cce74837a9cf5804eb205939b82227
• https://git.kernel.org/stable/c/f8654743a0e6909dc634cbfad6db6816f10f3399