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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id fw21sm6200587pjb.25.2021.11.10.12.17.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Nov 2021 12:17:35 -0800 (PST) Date: Wed, 10 Nov 2021 12:17:34 -0800 From: Kees Cook To: David Hildenbrand Cc: Yafang Shao , akpm@linux-foundation.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, Mathieu Desnoyers , Arnaldo Carvalho de Melo , Alexei Starovoitov , Andrii Nakryiko , Michal Miroslaw , Peter Zijlstra , Steven Rostedt , Matthew Wilcox , Al Viro , Petr Mladek Subject: Re: [PATCH 1/7] fs/exec: make __set_task_comm always set a nul terminated string Message-ID: <202111101215.A42612FEC@keescook> References: <20211108083840.4627-1-laoar.shao@gmail.com> <20211108083840.4627-2-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 971D8B0000B4 X-Stat-Signature: q9ipqz6ubbxm3xqjsiozisq4iojotkoz Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=g9lNF+pd; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf24.hostedemail.com: domain of keescook@chromium.org designates 209.85.216.46 as permitted sender) smtp.mailfrom=keescook@chromium.org X-HE-Tag: 1636575456-388624 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Nov 10, 2021 at 09:28:12AM +0100, David Hildenbrand wrote: > On 08.11.21 09:38, Yafang Shao wrote: > > Make sure the string set to task comm is always nul terminated. > > > > strlcpy: "the result is always a valid NUL-terminated string that fits > in the buffer" > > The only difference seems to be that strscpy_pad() pads the remainder > with zeroes. > > Is this description correct and I am missing something important? Yes, this makes sure it's zero padded just to be robust against full tsk->comm copies that got noticed in other places. The only other change is that we want to remove strlcpy() from the kernel generally since it can trigger out-of-bound reads on the source string[1]. So, in this case, the most robust version is to use strscpy_pad(). -Kees [1] https://github.com/KSPP/linux/issues/89 > > > Signed-off-by: Yafang Shao > > Reviewed-by: Kees Cook > > Cc: Mathieu Desnoyers > > Cc: Arnaldo Carvalho de Melo > > Cc: Alexei Starovoitov > > Cc: Andrii Nakryiko > > Cc: Michal Miroslaw > > Cc: Peter Zijlstra > > Cc: Steven Rostedt > > Cc: Matthew Wilcox > > Cc: David Hildenbrand > > Cc: Al Viro > > Cc: Kees Cook > > Cc: Petr Mladek > > --- > > fs/exec.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/exec.c b/fs/exec.c > > index a098c133d8d7..404156b5b314 100644 > > --- a/fs/exec.c > > +++ b/fs/exec.c > > @@ -1224,7 +1224,7 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec) > > { > > task_lock(tsk); > > trace_task_rename(tsk, buf); > > - strlcpy(tsk->comm, buf, sizeof(tsk->comm)); > > + strscpy_pad(tsk->comm, buf, sizeof(tsk->comm)); > > task_unlock(tsk); > > perf_event_comm(tsk, exec); > > } > > > > > -- > Thanks, > > David / dhildenb > -- Kees Cook