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Subject: [PATCH] jfs: fix use-after-free on log shutdown
Author: mashiro.chen@mailbox.org

During JFS log shutdown, log buffer pages can be freed while lower-layer
loop workers are still copying from them, triggering a use-after-free
reported by syzbot in copy_folio_from_iter_atomic().

Track in-flight log I/O in struct jfs_log and wait for completion before
freeing log buffers. Add io_inflight/io_waitq, increment io_inflight
before submitting BIOs in lbmRead() and lbmStartIO(), and decrement it
in lbmIODone() at the unified out: label, which all completion paths
including READ, DIRECT, synchronous, GC, asynchronous converge on.

This closes the teardown race between buffer page free and late I/O
completion.

Reported-by: syzbot+6cc93ec9a4035badb85f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6cc93ec9a4035badb85f
Signed-off-by: Mashiro Chen <mashiro.chen@mailbox.org>
---
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

 fs/jfs/jfs_logmgr.c | 11 +++++++++--
 fs/jfs/jfs_logmgr.h |  2 ++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
index 306165e61438..a567dae3b908 100644
--- a/fs/jfs/jfs_logmgr.c
+++ b/fs/jfs/jfs_logmgr.c
@@ -1804,6 +1804,8 @@ static int lbmLogInit(struct jfs_log * log)
 	 * avoid deadlock here.
 	 */
 	init_waitqueue_head(&log->free_wait);
+	init_waitqueue_head(&log->io_waitq);
+	atomic_set(&log->io_inflight, 0);
 
 	log->lbuf_free = NULL;
 
@@ -1855,6 +1857,8 @@ static void lbmLogShutdown(struct jfs_log * log)
 
 	jfs_info("lbmLogShutdown: log:0x%p", log);
 
+	wait_event(log->io_waitq, !atomic_read(&log->io_inflight));
+
 	lbuf = log->lbuf_free;
 	while (lbuf) {
 		struct lbuf *next = lbuf->l_freelist;
@@ -1976,6 +1980,7 @@ static int lbmRead(struct jfs_log * log, int pn, struct lbuf ** bpp)
 
 	bio->bi_end_io = lbmIODone;
 	bio->bi_private = bp;
+	atomic_inc(&log->io_inflight);
 	/*check if journaling to disk has been disabled*/
 	if (log->no_integrity) {
 		bio->bi_iter.bi_size = 0;
@@ -2122,6 +2127,7 @@ static void lbmStartIO(struct lbuf * bp)
 
 	bio->bi_end_io = lbmIODone;
 	bio->bi_private = bp;
+	atomic_inc(&log->io_inflight);
 
 	/* check if journaling to disk has been disabled */
 	if (log->no_integrity) {
@@ -2168,7 +2174,7 @@ static void lbmIODone(struct bio *bio)
 {
 	struct lbuf *bp = bio->bi_private;
 	struct lbuf *nextbp, *tail;
-	struct jfs_log *log;
+	struct jfs_log *log = bp->l_log;
 	unsigned long flags;
 
 	/*
@@ -2214,7 +2220,6 @@ static void lbmIODone(struct bio *bio)
 	INCREMENT(lmStat.pagedone);
 
 	/* update committed lsn */
-	log = bp->l_log;
 	log->clsn = (bp->l_pn << L2LOGPSIZE) + bp->l_ceor;
 
 	if (bp->l_flag & lbmDIRECT) {
@@ -2299,6 +2304,8 @@ static void lbmIODone(struct bio *bio)
 out:
 	bp->l_flag |= lbmDONE;
 	LCACHE_UNLOCK(flags);
+	if (atomic_dec_and_test(&log->io_inflight))
+		wake_up(&log->io_waitq);
 }
 
 int jfsIOWait(void *arg)
diff --git a/fs/jfs/jfs_logmgr.h b/fs/jfs/jfs_logmgr.h
index 09e0ef6aecce..31b826d546c0 100644
--- a/fs/jfs/jfs_logmgr.h
+++ b/fs/jfs/jfs_logmgr.h
@@ -400,6 +400,8 @@ struct jfs_log {
 	uuid_t uuid;		/* 16: 128-bit uuid of log device */
 
 	int no_integrity;	/* 3: flag to disable journaling to disk */
+	atomic_t io_inflight;
+	wait_queue_head_t io_waitq;
 };
 
 /*
-- 
2.54.0