CVE-2023-53447

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> f2fs: don&amp;#39;t reset unchangable mount option in f2fs_remount()<br /> <br /> syzbot reports a bug as below:<br /> <br /> general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] PREEMPT SMP KASAN<br /> RIP: 0010:__lock_acquire+0x69/0x2000 kernel/locking/lockdep.c:4942<br /> Call Trace:<br /> lock_acquire+0x1e3/0x520 kernel/locking/lockdep.c:5691<br /> __raw_write_lock include/linux/rwlock_api_smp.h:209 [inline]<br /> _raw_write_lock+0x2e/0x40 kernel/locking/spinlock.c:300<br /> __drop_extent_tree+0x3ac/0x660 fs/f2fs/extent_cache.c:1100<br /> f2fs_drop_extent_tree+0x17/0x30 fs/f2fs/extent_cache.c:1116<br /> f2fs_insert_range+0x2d5/0x3c0 fs/f2fs/file.c:1664<br /> f2fs_fallocate+0x4e4/0x6d0 fs/f2fs/file.c:1838<br /> vfs_fallocate+0x54b/0x6b0 fs/open.c:324<br /> ksys_fallocate fs/open.c:347 [inline]<br /> __do_sys_fallocate fs/open.c:355 [inline]<br /> __se_sys_fallocate fs/open.c:353 [inline]<br /> __x64_sys_fallocate+0xbd/0x100 fs/open.c:353<br /> do_syscall_x64 arch/x86/entry/common.c:50 [inline]<br /> do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80<br /> entry_SYSCALL_64_after_hwframe+0x63/0xcd<br /> <br /> The root cause is race condition as below:<br /> - since it tries to remount rw filesystem, so that do_remount won&amp;#39;t<br /> call sb_prepare_remount_readonly to block fallocate, there may be race<br /> condition in between remount and fallocate.<br /> - in f2fs_remount(), default_options() will reset mount option to default<br /> one, and then update it based on result of parse_options(), so there is<br /> a hole which race condition can happen.<br /> <br /> Thread A Thread B<br /> - f2fs_fill_super<br /> - parse_options<br /> - clear_opt(READ_EXTENT_CACHE)<br /> <br /> - f2fs_remount<br /> - default_options<br /> - set_opt(READ_EXTENT_CACHE)<br /> - f2fs_fallocate<br /> - f2fs_insert_range<br /> - f2fs_drop_extent_tree<br /> - __drop_extent_tree<br /> - __may_extent_tree<br /> - test_opt(READ_EXTENT_CACHE) return true<br /> - write_lock(&amp;et-&gt;lock) access NULL pointer<br /> - parse_options<br /> - clear_opt(READ_EXTENT_CACHE)