linux-kernel - [PATCH] gfs2: Fix memory leak in gfs2_trans

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Message-ID: <tencent_522CB56DC89514EA26EF8ACCAC784A6F540A@qq.com>
Date: Sat,  8 Nov 2025 17:13:30 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+63ba84f14f62e61a5fd0@...kaller.appspotmail.com
Cc: agruenba@...hat.com,
	gfs2@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH] gfs2: Fix memory leak in gfs2_trans_begin

According to log [1], a "bad magic number" was found when checking the
metatype, which caused gfs2 withdraw.

The root cause of the problem is: log flush treats non-delayed withdraw
as withdraw, resulting in no one reclaiming the memory of transaction.
See the call stack below for details.

	CPU1					CPU2
	====					====
gfs2_meta_buffer()
gfs2_metatype_check()
gfs2_metatype_check_i()
gfs2_metatype_check_ii()		gfs2_log_flush()
gfs2_withdraw()				tr = sdp->sd_log_tr
signal_our_withdraw()			sdp->sd_log_tr = NULL
gfs2_ail_drain()			goto out_withdraw
spin_unlock(&sdp->sd_ail_lock)    	trans_drain()
					spin_lock(&sdp->sd_ail_lock)
					list_add(&tr->tr_list, &sdp->sd_ail1_list)
					tr = NULL
					goto out_end

The original text suggests adding a delayed withdraw check to handle
transaction cases to avoid similar memory leaks.

syzbot reported:
[1]
gfs2: fsid=syz:syz.0: fatal: invalid metadata block - bh = 9381 (bad magic number), function = gfs2_meta_buffer, file = fs/gfs2/meta_io.c, line = 499

[2]
BUG: memory leak
unreferenced object 0xffff888126cf1000 (size 144):
  backtrace (crc f56b339f):
    gfs2_trans_begin+0x29/0xa0 fs/gfs2/trans.c:115
    alloc_dinode fs/gfs2/inode.c:418 [inline]
    gfs2_create_inode+0xca0/0x1890 fs/gfs2/inode.c:807


Fixes: f5456b5d67cf ("gfs2: Clean up revokes on normal withdraws")
Reported-by: syzbot+63ba84f14f62e61a5fd0@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=63ba84f14f62e61a5fd0
Tested-by: syzbot+63ba84f14f62e61a5fd0@...kaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
 fs/gfs2/log.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 115c4ac457e9..7bba7951dbdb 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -1169,11 +1169,13 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
 	 * never queued onto any of the ail lists. Here we add it to
 	 * ail1 just so that ail_drain() will find and free it.
 	 */
-	spin_lock(&sdp->sd_ail_lock);
-	if (tr && list_empty(&tr->tr_list))
-		list_add(&tr->tr_list, &sdp->sd_ail1_list);
-	spin_unlock(&sdp->sd_ail_lock);
-	tr = NULL;
+	if (gfs2_withdrawing(sdp)) {
+		spin_lock(&sdp->sd_ail_lock);
+		if (tr && list_empty(&tr->tr_list))
+			list_add(&tr->tr_list, &sdp->sd_ail1_list);
+		spin_unlock(&sdp->sd_ail_lock);
+		tr = NULL;
+	}
 	goto out_end;
 }
 
-- 
2.43.0