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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id h19sm22908045pfv.81.2021.10.25.14.08.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Oct 2021 14:08:58 -0700 (PDT) Date: Mon, 25 Oct 2021 14:08:57 -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 02/12] fs/exec: make __get_task_comm always get a nul terminated string Message-ID: <202110251408.2E661E70BC@keescook> References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-3-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211025083315.4752-3-laoar.shao@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 25, 2021 at 08:33:05AM +0000, Yafang Shao wrote: > If the dest buffer size is smaller than sizeof(tsk->comm), the buffer > will be without null ternimator, that may cause problem. We can make sure > the buffer size not smaller than comm at the callsite to avoid that > problem, but there may be callsite that we can't easily change. > > Using strscpy_pad() instead of strncpy() in __get_task_comm() can make > the string always nul ternimated. > > Suggested-by: Kees Cook > Suggested-by: Steven Rostedt > Signed-off-by: Yafang Shao > 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 > --- > fs/exec.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/exec.c b/fs/exec.c > index 404156b5b314..bf2a7a91eeea 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1209,7 +1209,8 @@ static int unshare_sighand(struct task_struct *me) > char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk) > { > task_lock(tsk); > - strncpy(buf, tsk->comm, buf_size); > + /* The copied value is always null terminated */ This may could say "always NUL terminated and zero-padded" > + strscpy_pad(buf, tsk->comm, buf_size); > task_unlock(tsk); > return buf; > } > -- > 2.17.1 > But for the replacement with strscpy_pad(), yes please: Reviewed-by: Kees Cook -- Kees Cook