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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TW17cz/EEZaZJmmAANQIcH721CVqiYs4LQJri53qVRx99HG1jZN0YeCm+1tRjrZ// Js/j4lVsCcFwwUP0dpNXXlxianCp7nwBPxuD13aaNZcrqJrHOkNKo88vzUd0slfVr4 OBXRpHcT8p4UmBYpoWowl95Q3YE2D0bTrkeJ2BuBy8SM8wPSFkeQxJ1D8JcAFVYk7+ WSbj5pSUAsPPICBiMuAfcU/14xU79isfbnly6OiAMYgg7uBvBnidj5xY6FrzxAIgzh z7fpjzt+CBzhIMAvNsmNP1tzvobW45LNqeGvkHyXv9OcMANdijzSMQAi4aw7aq8Uzz dIDSeiovGZNSA== Date: Thu, 24 Jul 2025 16:49:43 -0700 From: Kees Cook To: Bhupesh Cc: akpm@linux-foundation.org, kernel-dev@igalia.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, oliver.sang@intel.com, lkp@intel.com, laoar.shao@gmail.com, pmladek@suse.com, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, arnaldo.melo@gmail.com, alexei.starovoitov@gmail.com, andrii.nakryiko@gmail.com, mirq-linux@rere.qmqm.pl, peterz@infradead.org, willy@infradead.org, david@redhat.com, viro@zeniv.linux.org.uk, ebiederm@xmission.com, brauner@kernel.org, jack@suse.cz, mingo@redhat.com, juri.lelli@redhat.com, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-trace-kernel@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: [PATCH v6 2/3] treewide: Switch memcpy() users of 'task->comm' to a more safer implementation Message-ID: <202507241640.572BF86C70@keescook> References: <20250724123612.206110-1-bhupesh@igalia.com> <20250724123612.206110-3-bhupesh@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250724123612.206110-3-bhupesh@igalia.com> X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 7D2DB100007 X-Stat-Signature: 5xum3m3iy4pmg3nwsxstogzw1akx5zn7 X-HE-Tag: 1753400984-157063 X-HE-Meta: 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 CgO71v34 uGtVck0yieymZjoGs+OJZTUCEMVXfmTQ4ZKXFzzsWtXCqfQGWHKXS0PTIKpEtjvb344H6EBvR3waKCibMsk8UAKGFdSlsI1yS8+grPBdiPlRmStO8/X90mAQ8ukG4MEjg0Ug5jIuTDpAU+YktxGf1Qbzfwa/Pud3hkD8OKiH7jAGwBOJRgYO+QHd+Lsw3yAZxGMJzKRgpoBx+ftgIcL/kMfdsItcn94Qw18FGgKftJcg7uQe8mTaPUGd0QgEbSCKk8iwE0Xz8mFgG39sjZabuFooBtsKB2ci1jIEk7AFo+zZVy114rbUdgTVskQ21aPyW5CAPVaorYks+lNf+5kezhgPPbQ== 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: List-Subscribe: List-Unsubscribe: On Thu, Jul 24, 2025 at 06:06:11PM +0530, Bhupesh wrote: > As Linus mentioned in [1], currently we have several memcpy() use-cases > which use 'current->comm' to copy the task name over to local copies. > For an example: > > ... > char comm[TASK_COMM_LEN]; > memcpy(comm, current->comm, TASK_COMM_LEN); > ... > > These should be modified so that we can later implement approaches > to handle the task->comm's 16-byte length limitation (TASK_COMM_LEN) > in a more modular way (follow-up patch does the same): > > ... > char comm[TASK_COMM_LEN]; > memcpy(comm, current->comm, TASK_COMM_LEN); > comm[TASK_COMM_LEN - 1] = '\0'; > ... Why not switch all of these to get_task_comm()? It will correctly handle the size check and NUL termination. In an earlier thread[1], I pointed out that since __set_task_comm() always keeps a final NUL byte, we're always safe to use strscpy(). (We want to block over-reads and over-writes but don't care about garbled reads.) In the new case of copying into a smaller buffer, strscpy() will always handle writing the final NUL byte. The only special cases I can think of would be non-fixed-sized destination buffers, which get_task_comm() doesn't like since it can't validate how to safely terminate the buffer. The example you give above isn't that, though. -Kees [1] https://lore.kernel.org/all/202411301244.381F2B8D17@keescook/ -- Kees Cook