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>

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 8eb17cc7394165627f0bf4fb6b97a480a4cd0fa0..6e770f82d39f43a7e47e46b841215e81f965d002 100644 (file)
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -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 @@ try_onemore:
                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) {