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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id t3sm16694772pgu.87.2021.10.25.14.14.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Oct 2021 14:14:36 -0700 (PDT) Date: Mon, 25 Oct 2021 14:14:36 -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 , Vladimir Zapolskiy , David Howells Subject: Re: [PATCH v6 03/12] drivers/connector: make connector comm always nul ternimated Message-ID: <202110251411.93B477676B@keescook> References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-4-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211025083315.4752-4-laoar.shao@gmail.com> X-Stat-Signature: 3jf4ztbcjsigynscc6bbbyppwaoiqd96 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: DBF96B0000AF Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=eId9LLzy; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf19.hostedemail.com: domain of keescook@chromium.org designates 209.85.215.172 as permitted sender) smtp.mailfrom=keescook@chromium.org X-HE-Tag: 1635196473-221024 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 Mon, Oct 25, 2021 at 08:33:06AM +0000, Yafang Shao wrote: > connector comm was introduced in commit > f786ecba4158 ("connector: add comm change event report to proc connector"). > struct comm_proc_event was defined in include/linux/cn_proc.h first and > then been moved into file include/uapi/linux/cn_proc.h in commit > 607ca46e97a1 ("UAPI: (Scripted) Disintegrate include/linux"). > > As this is the UAPI code, we can't change it without potentially breaking > things (i.e. userspace binaries have this size built in, so we can't just > change the size). To prepare for the followup change - extending task > comm, we have to use __get_task_comm() to avoid the BUILD_BUG_ON() in > proc_comm_connector(). I wonder, looking at this again, if it might make more sense to avoid this cn_proc.c change, and instead, adjust get_task_comm() like so: #define get_task_comm(buf, tsk) __get_task_comm(buf, __must_be_array(buf) + sizeof(buf), tsk) This would still enforce the original goal of making sure get_task_comm() is being used on a char array, and now that __get_task_comm() will truncate & pad, it's safe to use on both too-small and too-big arrays. -- Kees Cook