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([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a8fede418sm13928485e9.6.2026.05.01.04.02.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 May 2026 04:02:04 -0700 (PDT) From: Tristan Madani To: Andreas Gruenbacher Cc: gfs2@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Tristan Madani , syzbot+42a37bf8045847d8f9d2@syzkaller.appspotmail.com Subject: [PATCH] gfs2: fix use-after-free in gfs2_qd_dealloc Date: Fri, 1 May 2026 11:02:03 +0000 Message-ID: <20260501110203.18771-1-tristmd@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: gfs2@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(), accesses the superblock object sdp through qd->qd_sbd after freeing qd. It does so to decrement sd_quota_count and wake up sd_kill_wait. However, by the time the RCU callback runs, gfs2_put_super() may have already freed sdp via free_sbd(). This can happen when gfs2_quota_cleanup() is called during unmount: it disposes of quota objects via call_rcu() and then waits on sd_kill_wait with a 60-second timeout. If the timeout expires, or if gfs2_gl_hash_clear() triggers additional qd_put() calls that schedule more RCU callbacks after the wait completes, gfs2_put_super() will proceed to free the superblock while RCU callbacks referencing it are still pending. Add an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure all pending RCU callbacks (including gfs2_qd_dealloc) have completed before the superblock is freed. Fixes: a475c5dd16e5 ("gfs2: Free quota data objects synchronously") Reported-by: syzbot+42a37bf8045847d8f9d2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=42a37bf8045847d8f9d2 Tested-by: syzbot+42a37bf8045847d8f9d2@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- fs/gfs2/super.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c index a2ea121331f18..4d854556b5299 100644 --- a/fs/gfs2/super.c +++ b/fs/gfs2/super.c @@ -643,6 +643,7 @@ static void gfs2_put_super(struct super_block *sb) gfs2_delete_debugfs_file(sdp); gfs2_sys_fs_del(sdp); + rcu_barrier(); free_sbd(sdp); } -- 2.47.3