linux-kernel - [PATCH 5.15.y] gfs2: Fix NULL pointer dereference in gfs2_log

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Message-Id: <20260205044147.1948143-1-black.hawk@163.com>
Date: Thu,  5 Feb 2026 12:41:47 +0800
From: Rahul Sharma <black.hawk@....com>
To: gregkh@...uxfoundation.org,
	stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Andreas Gruenbacher <agruenba@...hat.com>,
	Rahul Sharma <black.hawk@....com>
Subject: [PATCH 5.15.y] gfs2: Fix NULL pointer dereference in gfs2_log_flush

From: Andreas Gruenbacher <agruenba@...hat.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@...hat.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@....com>
---
 fs/gfs2/log.c   | 3 ++-
 fs/gfs2/super.c | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 9a96842aeab3..e7867b0f6c62 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -1094,7 +1094,8 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
 	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;
 
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 268651ac9fc8..3345bc071e44 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -67,9 +67,13 @@ void gfs2_jindex_free(struct gfs2_sbd *sdp)
 	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);
-- 
2.34.1