From nobody Thu Dec 26 11:49:18 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3EC1F29A0; Sat, 30 Nov 2024 04:49:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732942160; cv=none; b=aUDL8DZr9WfknPQW+e6htdl/O3kmSOWBzx5FLYESSmn52fJBvGL/RrNLQz1kSItjFsWjMtdpGuHIvgvCejVLohwLZELnREuc3zjvhRdJIAFLaDrwozUGKvQVgv3TkRGDzwfx3P0hL6sgEr31DA9DZOe0frzsO8g8oQfWPk7EwdY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732942160; c=relaxed/simple; bh=7a+G0bORdE2giUr3BfncHUbUhxIoNcU4LB5xeDPWjC0=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=cqOHN5yG8sbpqD5HIJj8xSr0eqW3CTm4xAS0Gsjrl9da/slCdeBrvooWE/HijI21FHos1bAQgnr/Mciu66qpsy9nns2+Qr6CUhBKu91J7r144oZaf/S3QZ/E6o23NtLl5KaJk4zlB5VhYXq+avCAmneF6pmNax+EQOMv42qDNaM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GI1wQ/YJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GI1wQ/YJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B319DC4CECC; Sat, 30 Nov 2024 04:49:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732942159; bh=7a+G0bORdE2giUr3BfncHUbUhxIoNcU4LB5xeDPWjC0=; h=From:To:Cc:Subject:Date:From; b=GI1wQ/YJnVYzohfA+pkUBuCpZ7wmxmedH3w63YwPYzewyxYdEl0OgB6j0OpKX69kP gHCQDqAsGzSlc7cSAnQx4/T++rPZOCA6VXS8vFoTxin2qWiLmfxBWIB4M0ggiKzcwG EALQDbzN0Gk3lZ8JTYwgfGYA/+FefzNwcO4MTFw1dSOceBPmUVLOHrPmalQ62C9l6i QUe4V2BmgIriWzUlbuc2osu6jamacQ4TlSkrNsWVvBZHm8vWf3GWqF5SwZl9GJzF2u b+fAt858jkaIDXPzS7VoWh+9H/2aWNuInIscckjflwohp4CUaA3Sjm72pUc6hot48/ W3imNrwytJ5sA== From: Kees Cook To: Eric Biederman Cc: Kees Cook , Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Jens Axboe , Pavel Begunkov , Andrew Morton , Chen Yu , Shuah Khan , =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , linux-kernel@vger.kernel.org, io-uring@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] exec: Make sure task->comm is always NUL-terminated Date: Fri, 29 Nov 2024 20:49:14 -0800 Message-Id: <20241130044909.work.541-kees@kernel.org> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4500; i=kees@kernel.org; h=from:subject:message-id; bh=7a+G0bORdE2giUr3BfncHUbUhxIoNcU4LB5xeDPWjC0=; b=owGbwMvMwCVmps19z/KJym7G02pJDOleM738HBLK3jN2iE/6eH1DywlDV//zrlOz/B20zoSrF TcWRqh2lLIwiHExyIopsgTZuce5eLxtD3efqwgzh5UJZAgDF6cATKSmnZFhhnD59S3JD5jX3D1Q mbmj6tqU1GW6Zs+WWgddMvkW5bPjByPDewHbf9LBK0Ic3Q08T3n7tfyLWvl1wUbxiKnnNR5G8O7 iAAA= X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Using strscpy() meant that the final character in task->comm may be non-NUL for a moment before the "string too long" truncation happens. Instead of adding a new use of the ambiguous strncpy(), we'd want to use memtostr_pad() which enforces being able to check at compile time that sizes are sensible, but this requires being able to see string buffer lengths. Instead of trying to inline __set_task_comm() (which needs to call trace and perf functions), just open-code it. But to make sure we're always safe, add compile-time checking like we already do for get_task_comm(). Suggested-by: Linus Torvalds Suggested-by: "Eric W. Biederman" Signed-off-by: Kees Cook --- Cc: Eric Biederman Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org Here's what I'd prefer to use to clean up set_task_comm(). I merged Linus and Eric's suggestions and open-coded memtostr_pad(). --- fs/exec.c | 12 ++++++------ include/linux/sched.h | 9 ++++----- io_uring/io-wq.c | 2 +- io_uring/sqpoll.c | 2 +- kernel/kthread.c | 3 ++- 5 files changed, 14 insertions(+), 14 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index e0435b31a811..5f16500ac325 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1200,16 +1200,16 @@ char *__get_task_comm(char *buf, size_t buf_size, s= truct task_struct *tsk) EXPORT_SYMBOL_GPL(__get_task_comm); =20 /* - * These functions flushes out all traces of the currently running executa= ble - * so that a new one can be started + * This is unlocked -- the string will always be NUL-terminated, but + * may show overlapping contents if racing concurrent reads. */ - void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec) { - task_lock(tsk); + size_t len =3D min(strlen(buf), sizeof(tsk->comm) - 1); + trace_task_rename(tsk, buf); - strscpy_pad(tsk->comm, buf, sizeof(tsk->comm)); - task_unlock(tsk); + memcpy(tsk->comm, buf, len); + memset(&tsk->comm[len], 0, sizeof(tsk->comm) - len); perf_event_comm(tsk, exec); } =20 diff --git a/include/linux/sched.h b/include/linux/sched.h index e6ee4258169a..ac9f429ddc17 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1932,11 +1932,10 @@ static inline void kick_process(struct task_struct = *tsk) { } #endif =20 extern void __set_task_comm(struct task_struct *tsk, const char *from, boo= l exec); - -static inline void set_task_comm(struct task_struct *tsk, const char *from) -{ - __set_task_comm(tsk, from, false); -} +#define set_task_comm(tsk, from) ({ \ + BUILD_BUG_ON(sizeof(from) !=3D TASK_COMM_LEN); \ + __set_task_comm(tsk, from, false); \ +}) =20 extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk= ); #define get_task_comm(buf, tsk) ({ \ diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index a38f36b68060..5d0928f37471 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -634,7 +634,7 @@ static int io_wq_worker(void *data) struct io_wq_acct *acct =3D io_wq_get_acct(worker); struct io_wq *wq =3D worker->wq; bool exit_mask =3D false, last_timeout =3D false; - char buf[TASK_COMM_LEN]; + char buf[TASK_COMM_LEN] =3D {}; =20 set_mask_bits(&worker->flags, 0, BIT(IO_WORKER_F_UP) | BIT(IO_WORKER_F_RUNNING)); diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c index a26593979887..90011f06c7fb 100644 --- a/io_uring/sqpoll.c +++ b/io_uring/sqpoll.c @@ -271,7 +271,7 @@ static int io_sq_thread(void *data) struct io_ring_ctx *ctx; struct rusage start; unsigned long timeout =3D 0; - char buf[TASK_COMM_LEN]; + char buf[TASK_COMM_LEN] =3D {}; DEFINE_WAIT(wait); =20 /* offload context creation failed, just exit */ diff --git a/kernel/kthread.c b/kernel/kthread.c index db4ceb0f503c..162d55811744 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -736,10 +736,11 @@ EXPORT_SYMBOL(kthread_stop_put); =20 int kthreadd(void *unused) { + static const char comm[TASK_COMM_LEN] =3D "kthreadd"; struct task_struct *tsk =3D current; =20 /* Setup a clean context for our children to inherit. */ - set_task_comm(tsk, "kthreadd"); + set_task_comm(tsk, comm); ignore_signals(tsk); set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD)); set_mems_allowed(node_states[N_MEMORY]); --=20 2.34.1