[PATCH 6.1 263/280] gfs2: Fix NULL pointer dereference in gfs2_log_flush

Greg Kroah-Hartman
2026-02-04T15:17:59Z

From: Andreas Gruenbacher <agruenba@redhat.com>

[ Upstream commit 35264909e9d1973ab9aaa2a1b07cda70f12bb828 ]

In gfs2_jindex_free(), set sdp->sd_jdesc to NULL under the log flush
lock to provide exclusion against gfs2_log_flush().

In gfs2_log_flush(), check if sdp->sd_jdesc is non-NULL before
dereferencing it. Otherwise, we could run into a NULL pointer
dereference when outstanding glock work races with an unmount
(glock_work_func -> run_queue -> do_xmote -> inode_go_sync ->
gfs2_log_flush).

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
[ The context change is due to the commit 4d927b03a688
("gfs2: Rename gfs2_withdrawn to gfs2_withdrawing_or_withdrawn") in v6.8
which is irrelevant to the logic of this patch. ]
Signed-off-by: Rahul Sharma <black.hawk@163.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/gfs2/log.c | 3 ++-
fs/gfs2/super.c | 4 ++++
2 files changed, 6 insertions(+), 1 deletion(-)

--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -1102,7 +1102,8 @@ repeat:
lops_before_commit(sdp, tr);
if (gfs2_withdrawn(sdp))
goto out_withdraw;
- gfs2_log_submit_bio(&sdp->sd_jdesc->jd_log_bio, REQ_OP_WRITE);
+ if (sdp->sd_jdesc)
+ gfs2_log_submit_bio(&sdp->sd_jdesc->jd_log_bio, REQ_OP_WRITE);
if (gfs2_withdrawn(sdp))
goto out_withdraw;

--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -67,9 +67,13 @@ void gfs2_jindex_free(struct gfs2_sbd *s
sdp->sd_journals = 0;
spin_unlock(&sdp->sd_jindex_spin);

+ down_write(&sdp->sd_log_flush_lock);
sdp->sd_jdesc = NULL;
+ up_write(&sdp->sd_log_flush_lock);
+
while (!list_empty(&list)) {
jd = list_first_entry(&list, struct gfs2_jdesc, jd_list);
+ BUG_ON(jd->jd_log_bio);
gfs2_free_journal_extents(jd);
list_del(&jd->jd_list);
iput(jd->jd_inode);