[PATCH] jfs: drain lazy commit queue during unmount to prevent use-after-free

Tristan Madani
2026-05-01T11:02:39Z

The jfsCommit kernel thread processes committed transactions from
TxAnchor.unlock_queue via jfs_lazycommit(). During filesystem
unmount, jfs_umount() calls jfs_flush_journal(log, 2) which waits
for the log commit queue (log->cqueue) to drain. However, after
log I/O completes, lazy transactions are moved to
TxAnchor.unlock_queue for asynchronous processing by jfsCommit.

If jfs_umount() proceeds to free the jfs_log (via lmLogClose) or
jfs_sb_info (via kfree in jfs_put_super) while entries referencing
this superblock remain on unlock_queue, the jfsCommit thread will
access freed memory when it later processes these entries:

- jfs_lazycommit reads sbi->commit_state (UAF of jfs_sb_info)
- txLazyCommit accesses JFS_SBI(tblk->sb)->log and takes
log->gclock (UAF of jfs_log)

Add txLazyDrain() which waits for all entries in
TxAnchor.unlock_queue belonging to the unmounting superblock to be
processed, and also waits for any in-flight txLazyCommit
(IN_LAZYCOMMIT) for this superblock to complete. Call it from both
jfs_umount() and jfs_umount_rw() after jfs_flush_journal().

Reported-by: syzbot+c244f4a09ca85dd2ebc1@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c244f4a09ca85dd2ebc1
Tested-by: syzbot+c244f4a09ca85dd2ebc1@syzkaller.appspotmail.com
Reported-by: syzbot+885a4f3281b8d99c48d8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=885a4f3281b8d99c48d8
Tested-by: syzbot+885a4f3281b8d99c48d8@syzkaller.appspotmail.com
Fixes: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
fs/jfs/jfs_txnmgr.c | 35 +++++++++++++++++++++++++++++++++++
fs/jfs/jfs_txnmgr.h | 1 +
fs/jfs/jfs_umount.c | 8 ++++++++
3 files changed, 44 insertions(+)

diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
index 083dbbb0c3268..67a9908b5a4d9 100644
--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -2791,6 +2791,41 @@ void txLazyUnlock(struct tblock * tblk)
LAZY_UNLOCK(flags);
}

+
+/*
+ * txLazyDrain
+ *
+ * Wait for all pending lazy commit entries for this superblock
+ * to be processed by the jfsCommit thread. Must be called
+ * before freeing per-filesystem structures during unmount.
+ */
+void txLazyDrain(struct super_block *sb)
+{
+ struct jfs_sb_info *sbi = JFS_SBI(sb);
+ struct tblock *tblk;
+ unsigned long flags;
+ bool found;
+
+ do {
+ found = false;
+ LAZY_LOCK(flags);
+ list_for_each_entry(tblk, &TxAnchor.unlock_queue, cqueue) {
+ if (tblk->sb == sb) {
+ found = true;
+ break;
+ }
+ }
+ if (!found && (sbi->commit_state & IN_LAZYCOMMIT))
+ found = true;
+ LAZY_UNLOCK(flags);
+
+ if (found) {
+ wake_up(&jfs_commit_thread_wait);
+ schedule_timeout_uninterruptible(1);
+ }
+ } while (found);
+}
+
static void LogSyncRelease(struct metapage * mp)
{
struct jfs_log *log = mp->log;
diff --git a/fs/jfs/jfs_txnmgr.h b/fs/jfs/jfs_txnmgr.h
index ba71eb5ced567..fbbaed26c52bd 100644
--- a/fs/jfs/jfs_txnmgr.h
+++ b/fs/jfs/jfs_txnmgr.h
@@ -291,6 +291,7 @@ extern void txFreelock(struct inode *);
extern int lmLog(struct jfs_log *, struct tblock *, struct lrd *,
struct tlock *);
extern void txQuiesce(struct super_block *);
+extern void txLazyDrain(struct super_block *sb);
extern void txResume(struct super_block *);
extern void txLazyUnlock(struct tblock *);
extern int jfs_lazycommit(void *);
diff --git a/fs/jfs/jfs_umount.c b/fs/jfs/jfs_umount.c
index 18569f1eaabdb..657707361be2a 100644
--- a/fs/jfs/jfs_umount.c
+++ b/fs/jfs/jfs_umount.c
@@ -58,6 +58,13 @@ int jfs_umount(struct super_block *sb)
*/
jfs_flush_journal(log, 2);

+ /*
+ * Drain any pending lazy commit entries for this filesystem so
+ * the jfsCommit thread does not access freed structures.
+ */
+ if (log)
+ txLazyDrain(sb);
+
/*
* Hold log lock so write_special_inodes (lmLogSync) cannot see
* this sbi with a NULL inode pointer while iterating log->sb_list.
@@ -142,6 +149,7 @@ int jfs_umount_rw(struct super_block *sb)
* remove file system from log active file system list.
*/
jfs_flush_journal(log, 2);
+ txLazyDrain(sb);

/*
* Make sure all metadata makes it to disk
--
2.47.3