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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id a20sm19562774pfn.136.2021.10.25.14.35.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Oct 2021 14:35:43 -0700 (PDT) Date: Mon, 25 Oct 2021 14:35:42 -0700 From: Kees Cook To: Yafang Shao Cc: akpm@linux-foundation.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, arnaldo.melo@gmail.com, pmladek@suse.com, peterz@infradead.org, viro@zeniv.linux.org.uk, valentin.schneider@arm.com, qiang.zhang@windriver.com, robdclark@chromium.org, christian@brauner.io, dietmar.eggemann@arm.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, davem@davemloft.net, kuba@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, dennis.dalessandro@cornelisnetworks.com, mike.marciniszyn@cornelisnetworks.com, dledford@redhat.com, jgg@ziepe.ca, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, oliver.sang@intel.com, lkp@intel.com, Andrii Nakryiko Subject: Re: [PATCH v6 12/12] kernel/kthread: show a warning if kthread's comm is truncated Message-ID: <202110251431.F594652F@keescook> References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-13-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211025083315.4752-13-laoar.shao@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 25, 2021 at 08:33:15AM +0000, Yafang Shao wrote: > Show a warning if task comm is truncated. Below is the result > of my test case: > > truncated kthread comm:I-am-a-kthread-with-lon, pid:14 by 6 characters > > Suggested-by: Petr Mladek > Signed-off-by: Yafang Shao > Reviewed-by: Kees Cook > Cc: Mathieu Desnoyers > Cc: Arnaldo Carvalho de Melo > Cc: Andrii Nakryiko > Cc: Peter Zijlstra > Cc: Steven Rostedt > Cc: Al Viro > Cc: Kees Cook > Cc: Petr Mladek > --- > kernel/kthread.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/kernel/kthread.c b/kernel/kthread.c > index 5b37a8567168..46b924c92078 100644 > --- a/kernel/kthread.c > +++ b/kernel/kthread.c > @@ -399,12 +399,17 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), > if (!IS_ERR(task)) { > static const struct sched_param param = { .sched_priority = 0 }; > char name[TASK_COMM_LEN]; > + int len; > > /* > * task is already visible to other tasks, so updating > * COMM must be protected. > */ > - vsnprintf(name, sizeof(name), namefmt, args); > + len = vsnprintf(name, sizeof(name), namefmt, args); > + if (len >= TASK_COMM_LEN) { And since this failure case is slow-path, we could improve the warning as other had kind of suggested earlier with something like this instead: char *full_comm; full_comm = kvasprintf(GFP_KERNEL, namefmt, args); pr_warn("truncated kthread comm '%s' to '%s' (pid:%d)\n", full_comm, name); kfree(full_comm); } > set_task_comm(task, name); > /* > * root may have changed our (kthreadd's) priority or CPU mask. > -- > 2.17.1 > -- Kees Cook