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([43.153.32.141]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b73a6925d3sm17964031eec.7.2026.01.27.07.04.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jan 2026 07:04:53 -0800 (PST) From: alexjlzheng@gmail.com X-Google-Original-From: alexjlzheng@tencent.com To: oleg@redhat.com, usamaarif642@gmail.com, david@kernel.org, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, alexjlzheng@tencent.com, mingo@kernel.org, ruippan@tencent.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH] procfs: fix missing RCU protection when reading real_parent in do_task_stat() Date: Tue, 27 Jan 2026 23:04:50 +0800 Message-ID: <20260127150450.2073236-1-alexjlzheng@tencent.com> X-Mailer: git-send-email 2.49.0 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" From: Jinliang Zheng When reading /proc/[pid]/stat, do_task_stat() accesses task->real_parent without proper RCU protection, which leads: cpu 0 cpu 1 ----- ----- do_task_stat var =3D task->real_parent release_task call_rcu(delayed_put_task_struct) task_tgid_nr_ns(var) rcu_read_lock <--- Too late! task_pid_ptr <--- UAF! rcu_read_unlock This fix adds proper RCU protection similar to getppid() in kernel/sys.c which correctly uses rcu_dereference() when accessing current->real_parent. Fixes: 06fffb1267c9 ("do_task_stat: don't take rcu_read_lock()") Signed-off-by: Jinliang Zheng --- fs/proc/array.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/proc/array.c b/fs/proc/array.c index 42932f88141a..3c2eea2c551a 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -528,7 +528,9 @@ static int do_task_stat(struct seq_file *m, struct pid_= namespace *ns, } =20 sid =3D task_session_nr_ns(task, ns); - ppid =3D task_tgid_nr_ns(task->real_parent, ns); + rcu_read_lock(); + ppid =3D task_tgid_nr_ns(rcu_dereference(task->real_parent), ns); + rcu_read_unlock(); pgid =3D task_pgrp_nr_ns(task, ns); =20 unlock_task_sighand(task, &flags); --=20 2.39.3