linux-kernel - [PATCH AUTOSEL 4.19 11/12] gfs2: Refcounting fix in gfs2_thaw

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Date: Mon, 15 Jan 2024 19:28:04 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Andreas Gruenbacher <agruenba@...hat.com>,
	Sasha Levin <sashal@...nel.org>,
	gfs2@...ts.linux.dev
Subject: [PATCH AUTOSEL 4.19 11/12] gfs2: Refcounting fix in gfs2_thaw_super

From: Andreas Gruenbacher <agruenba@...hat.com>

[ Upstream commit 4e58543e7da4859c4ba61d15493e3522b6ad71fd ]

It turns out that the .freeze_super and .thaw_super operations require
the filesystem to manage the superblock refcount itself.  We are using
the freeze_super() and thaw_super() helpers to mostly take care of that
for us, but this means that the superblock may no longer be around by
when thaw_super() returns, and gfs2_thaw_super() will then access freed
memory.  Take an extra superblock reference in gfs2_thaw_super() to fix
that.

Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/gfs2/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 29157f7d9663..2993598d18a4 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1013,6 +1013,7 @@ static int gfs2_freeze(struct super_block *sb)
 		goto out;
 	}
 
+	atomic_inc(&sb->s_active);
 	for (;;) {
 		error = gfs2_lock_fs_check_clean(sdp, &sdp->sd_freeze_gh);
 		if (!error)
@@ -1034,6 +1035,7 @@ static int gfs2_freeze(struct super_block *sb)
 	error = 0;
 out:
 	mutex_unlock(&sdp->sd_freeze_mutex);
+	deactivate_super(sb);
 	return error;
 }
 
-- 
2.43.0