[PATCH 6.1 121/127] f2fs: dont reset unchangable mount option in f2fs_remount()

Greg Kroah-Hartman
2023-08-09T10:56:51Z

From: Chao Yu <chao@kernel.org>

[ Upstream commit 458c15dfbce62c35fefd9ca637b20a051309c9f1 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/super.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 36bb1c969e8bb..ff47aad636e5b 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2040,9 +2040,22 @@ 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
@@ -2065,23 +2078,16 @@ 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_sb_has_readonly(sbi) && !f2fs_readonly(sbi->sb))
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);
@@ -2253,7 +2259,7 @@ 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);
@@ -4150,7 +4156,7 @@ 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) {
--
2.40.1