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Thu, 13 Aug 2026 19:50:11 -0700 (PDT) Received: from i4-l-hqh5357-03.ad.psu.edu ([130.203.139.71]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-90a935a2bf4sm4949026d6.49.2026.08.13.19.50.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Aug 2026 19:50:11 -0700 (PDT) From: Shuangpeng Bai To: agruenba@redhat.com Cc: gfs2@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Shuangpeng Bai Subject: [PATCH] gfs2: Fix use-after-free in glockfd iterator Date: Thu, 13 Aug 2026 22:49:33 -0400 Message-ID: <20260814024933.2791706-1-shuangpeng.kernel@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" gfs2_glockfd_seq_stop() drops the file and task references held by the iterator, but leaves both pointers unchanged. seq_file can invoke the iterator again after stop, for example after a bounded read followed by a rewind. The next start then drops the stale task reference again in gfs2_glockfd_next_task(), and can similarly drop the stale file reference in gfs2_glockfd_next_file(). A duplicate task put can queue the task_struct for RCU freeing before fget_task_next() uses it. Clear both pointers when releasing their references so later iterator callbacks cannot put them again. Fixes: 4480c27ca3ea ("gfs2: Add glockfd debugfs file") Cc: stable@vger.kernel.org Signed-off-by: Shuangpeng Bai --- fs/gfs2/glock.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index b8a144d3a73b..283c5701dc1a 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -2734,10 +2734,14 @@ static void gfs2_glockfd_seq_stop(struct seq_file *= seq, void *iter_ptr) { struct gfs2_glockfd_iter *i =3D seq->private; =20 - if (i->file) + if (i->file) { fput(i->file); - if (i->task) + i->file =3D NULL; + } + if (i->task) { put_task_struct(i->task); + i->task =3D NULL; + } } =20 static void gfs2_glockfd_seq_show_flock(struct seq_file *seq, --=20 2.43.0