Commit 458c15df authored May 23, 2023 by Chao Yu Committed by Jaegeuk Kim Jun 12, 2023

f2fs: don't reset unchangable mount option in f2fs_remount()



syzbot reports a bug as below:

general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:__lock_acquire+0x69/0x2000 kernel/locking/lockdep.c:4942
Call Trace:
 lock_acquire+0x1e3/0x520 kernel/locking/lockdep.c:5691
 __raw_write_lock include/linux/rwlock_api_smp.h:209 [inline]
 _raw_write_lock+0x2e/0x40 kernel/locking/spinlock.c:300
 __drop_extent_tree+0x3ac/0x660 fs/f2fs/extent_cache.c:1100
 f2fs_drop_extent_tree+0x17/0x30 fs/f2fs/extent_cache.c:1116
 f2fs_insert_range+0x2d5/0x3c0 fs/f2fs/file.c:1664
 f2fs_fallocate+0x4e4/0x6d0 fs/f2fs/file.c:1838
 vfs_fallocate+0x54b/0x6b0 fs/open.c:324
 ksys_fallocate fs/open.c:347 [inline]
 __do_sys_fallocate fs/open.c:355 [inline]
 __se_sys_fallocate fs/open.c:353 [inline]
 __x64_sys_fallocate+0xbd/0x100 fs/open.c:353
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The root cause is race condition as below:
- since it tries to remount rw filesystem, so that do_remount won't
call sb_prepare_remount_readonly to block fallocate, there may be race
condition in between remount and fallocate.
- in f2fs_remount(), default_options() will reset mount option to default
one, and then update it based on result of parse_options(), so there is
a hole which race condition can happen.

Thread A			Thread B
- f2fs_fill_super
 - parse_options
  - clear_opt(READ_EXTENT_CACHE)

- f2fs_remount
 - default_options
  - set_opt(READ_EXTENT_CACHE)
				- f2fs_fallocate
				 - f2fs_insert_range
				  - f2fs_drop_extent_tree
				   - __drop_extent_tree
				    - __may_extent_tree
				     - test_opt(READ_EXTENT_CACHE) return true
				    - write_lock(&et->lock) access NULL pointer
 - parse_options
  - clear_opt(READ_EXTENT_CACHE)

Cc: <stable@vger.kernel.org>
Reported-by:  <syzbot+d015b6c2fbb5c383bf08@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/linux-f2fs-devel/20230522124203.3838360-1-chao@kernel.org


Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

parent d8189834

fs/f2fs/super.c

+18 −12

Original line number	Diff line number	Diff line
		@@ -2086,9 +2086,22 @@ static int f2fs_show_options(struct seq_file seq, struct dentry root)
		return 0;
		}

		static void default_options(struct f2fs_sb_info *sbi)
		static void default_options(struct f2fs_sb_info *sbi, bool remount)
		{
		/* init some FS parameters */
		if (!remount) {
		set_opt(sbi, READ_EXTENT_CACHE);
		clear_opt(sbi, DISABLE_CHECKPOINT);

		if (f2fs_hw_support_discard(sbi) \|\| f2fs_hw_should_discard(sbi))
		set_opt(sbi, DISCARD);

		if (f2fs_sb_has_blkzoned(sbi))
		F2FS_OPTION(sbi).discard_unit = DISCARD_UNIT_SECTION;
		else
		F2FS_OPTION(sbi).discard_unit = DISCARD_UNIT_BLOCK;
		}

		if (f2fs_sb_has_readonly(sbi))
		F2FS_OPTION(sbi).active_logs = NR_CURSEG_RO_TYPE;
		else
		@@ -2118,23 +2131,16 @@ static void default_options(struct f2fs_sb_info *sbi)
		set_opt(sbi, INLINE_XATTR);
		set_opt(sbi, INLINE_DATA);
		set_opt(sbi, INLINE_DENTRY);
		set_opt(sbi, READ_EXTENT_CACHE);
		set_opt(sbi, NOHEAP);
		clear_opt(sbi, DISABLE_CHECKPOINT);
		set_opt(sbi, MERGE_CHECKPOINT);
		F2FS_OPTION(sbi).unusable_cap = 0;
		sbi->sb->s_flags \|= SB_LAZYTIME;
		if (!f2fs_is_readonly(sbi))
		set_opt(sbi, FLUSH_MERGE);
		if (f2fs_hw_support_discard(sbi) \|\| f2fs_hw_should_discard(sbi))
		set_opt(sbi, DISCARD);
		if (f2fs_sb_has_blkzoned(sbi)) {
		if (f2fs_sb_has_blkzoned(sbi))
		F2FS_OPTION(sbi).fs_mode = FS_MODE_LFS;
		F2FS_OPTION(sbi).discard_unit = DISCARD_UNIT_SECTION;
		} else {
		else
		F2FS_OPTION(sbi).fs_mode = FS_MODE_ADAPTIVE;
		F2FS_OPTION(sbi).discard_unit = DISCARD_UNIT_BLOCK;
		}

		#ifdef CONFIG_F2FS_FS_XATTR
		set_opt(sbi, XATTR_USER);
		@@ -2306,7 +2312,7 @@ static int f2fs_remount(struct super_block sb, int flags, char *data)
		clear_sbi_flag(sbi, SBI_NEED_SB_WRITE);
		}

		default_options(sbi);
		default_options(sbi, true);

		/* parse mount options */
		err = parse_options(sb, data, true);
		@@ -4346,7 +4352,7 @@ static int f2fs_fill_super(struct super_block sb, void data, int silent)
		sbi->s_chksum_seed = f2fs_chksum(sbi, ~0, raw_super->uuid,
		sizeof(raw_super->uuid));

		default_options(sbi);
		default_options(sbi, false);
		/* parse mount options */
		options = kstrdup((const char *)data, GFP_KERNEL);
		if (data && !options) {