CVE-2024-47689

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> f2fs: fix to don&amp;#39;t set SB_RDONLY in f2fs_handle_critical_error()<br /> <br /> syzbot reports a f2fs bug as below:<br /> <br /> ------------[ cut here ]------------<br /> WARNING: CPU: 1 PID: 58 at kernel/rcu/sync.c:177 rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177<br /> CPU: 1 UID: 0 PID: 58 Comm: kworker/1:2 Not tainted 6.10.0-syzkaller-12562-g1722389b0d86 #0<br /> Workqueue: events destroy_super_work<br /> RIP: 0010:rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177<br /> Call Trace:<br /> percpu_free_rwsem+0x41/0x80 kernel/locking/percpu-rwsem.c:42<br /> destroy_super_work+0xec/0x130 fs/super.c:282<br /> process_one_work kernel/workqueue.c:3231 [inline]<br /> process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312<br /> worker_thread+0x86d/0xd40 kernel/workqueue.c:3390<br /> kthread+0x2f0/0x390 kernel/kthread.c:389<br /> ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147<br /> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244<br /> <br /> As Christian Brauner pointed out [1]: the root cause is f2fs sets<br /> SB_RDONLY flag in internal function, rather than setting the flag<br /> covered w/ sb-&gt;s_umount semaphore via remount procedure, then below<br /> race condition causes this bug:<br /> <br /> - freeze_super()<br /> - sb_wait_write(sb, SB_FREEZE_WRITE)<br /> - sb_wait_write(sb, SB_FREEZE_PAGEFAULT)<br /> - sb_wait_write(sb, SB_FREEZE_FS)<br /> - f2fs_handle_critical_error<br /> - sb-&gt;s_flags |= SB_RDONLY<br /> - thaw_super<br /> - thaw_super_locked<br /> - sb_rdonly() is true, so it skips<br /> sb_freeze_unlock(sb, SB_FREEZE_FS)<br /> - deactivate_locked_super<br /> <br /> Since f2fs has almost the same logic as ext4 [2] when handling critical<br /> error in filesystem if it mounts w/ errors=remount-ro option:<br /> - set CP_ERROR_FLAG flag which indicates filesystem is stopped<br /> - record errors to superblock<br /> - set SB_RDONLY falg<br /> Once we set CP_ERROR_FLAG flag, all writable interfaces can detect the<br /> flag and stop any further updates on filesystem. So, it is safe to not<br /> set SB_RDONLY flag, let&amp;#39;s remove the logic and keep in line w/ ext4 [3].<br /> <br /> [1] https://lore.kernel.org/all/20240729-himbeeren-funknetz-96e62f9c7aee@brauner<br /> [2] https://lore.kernel.org/all/20240729132721.hxih6ehigadqf7wx@quack3<br /> [3] https://lore.kernel.org/linux-ext4/20240805201241.27286-1-jack@suse.cz