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([147.46.174.222]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c164fa00b3sm158987715ad.32.2026.06.07.22.00.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Jun 2026 22:00:40 -0700 (PDT) From: Sechang Lim To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi Cc: Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Juntong Deng , Leon Hwang , bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf v4] bpf: fix NULL pointer dereference in bpf_task_from_vpid() Date: Mon, 8 Jun 2026 05:00:00 +0000 Message-ID: <20260608050001.2545245-1-rhkrqnwk98@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" bpf_task_from_vpid() looks up a task in the pid namespace of the current task, via find_task_by_vpid(): find_task_by_vpid(vpid) find_task_by_pid_ns(vpid, task_active_pid_ns(current)) find_pid_ns(nr, ns) -> idr_find(&ns->idr, nr) cgroup_skb programs run in softirq, which may interrupt a task that is itself in do_exit(). Once that task has passed exit_notify() -> release_task() -> __unhash_process(), its thread_pid is cleared, so task_active_pid_ns(current) returns NULL and find_pid_ns() dereferences &NULL->idr: BUG: kernel NULL pointer dereference, address: 0000000000000050 RIP: 0010:idr_find+0x11/0x30 lib/idr.c:176 Call Trace: find_pid_ns kernel/pid.c:370 [inline] find_task_by_pid_ns+0x3b/0xe0 kernel/pid.c:485 bpf_task_from_vpid+0x5b/0x200 kernel/bpf/helpers.c:2916 bpf_prog_run_array_cg+0x17e/0x530 kernel/bpf/cgroup.c:81 __cgroup_bpf_run_filter_skb+0x12b/0x250 kernel/bpf/cgroup.c:1612 sk_filter_trim_cap+0x1dc/0x4c0 net/core/filter.c:148 tcp_v4_rcv+0x18d1/0x2200 net/ipv4/tcp_ipv4.c:2223 do_exit+0xa63/0x1270 kernel/exit.c:1010 get_signal+0x141c/0x1530 kernel/signal.c:3037 Bail out when current has no pid namespace. Fixes: 675c3596ff32 ("bpf: Add bpf_task_from_vpid() kfunc") Signed-off-by: Sechang Lim Acked-by: Leon Hwang --- v4: - Drop the in_interrupt() check. (Kumar Kartikeya Dwivedi) - Switch to guard(rcu)() and drop the explicit rcu_read_unlock(). (Leon Hwang) v3: - https://lore.kernel.org/bpf/20260606091941.1803115-1-rhkrqnwk98@gmail.co= m/ v2: - https://lore.kernel.org/bpf/20260605200501.1619406-1-rhkrqnwk98@gmail.co= m/ v1: - https://lore.kernel.org/bpf/20260603204206.773482-1-rhkrqnwk98@gmail.com/ kernel/bpf/helpers.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index b5314c9fed3c..80aa3bf203b0 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2912,11 +2912,13 @@ __bpf_kfunc struct task_struct *bpf_task_from_vpid(= s32 vpid) { struct task_struct *p; =20 - rcu_read_lock(); + guard(rcu)(); + if (!task_active_pid_ns(current)) + return NULL; + p =3D find_task_by_vpid(vpid); if (p) p =3D bpf_task_acquire(p); - rcu_read_unlock(); =20 return p; } --=20 2.43.0