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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747972127; bh=hU4E11daZQRWPop+eXf7dItbrTLSr07eegr9d9rLyLc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lj/rQ3GiGLdiau+P57zmneGhBgAfMwOjMvBLctFhT75R1EPvZ5B+giVnFwI5eHxa9 RiMiquG8Ahu7fzGgL53Px/BnaD5MqSe+XkulE8WW3VtGLO3jgYvTq7mHJmnXO8HT0k IVlm+pa2SWgRZfx0S+157FDTqcymr66Laaajra42Cmav0gUZ5rF4VwxfkSUBOljdMj Zu+1bGtmcY67IjZpTYe/CyKwnE1FIQawVg8S5ZD4PBl0KY2UIPvReTE3pKq0rTvPqd l4BA/NIs6ebHPA4YP0vqH8f8LYR9cjI9h0XPmOzzN1clAgzBOWk0XqocxYh+JpDqIl CK9+q1olWtQ9g== Date: Thu, 22 May 2025 20:48:44 -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 Subject: Re: [PATCH v4 3/3] exec: Add support for 64 byte 'tsk->comm_ext' Message-ID: <202505222041.B639D482FB@keescook> References: <20250521062337.53262-1-bhupesh@igalia.com> <20250521062337.53262-4-bhupesh@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250521062337.53262-4-bhupesh@igalia.com> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 1AE6E20007 X-Stat-Signature: g3hq64my5ko1ciss7stcm746cgtns5y6 X-Rspam-User: X-HE-Tag: 1747972128-5477 X-HE-Meta: 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 Z1smaJQx YAfenitiW+V/uyEQoz3yTgVSge/tAwlGtxlZepG55QE93oP/or1TSPsKQ4jO+9cnMDGF+paWnGDqL5DxJb0WT94ALCPzDLrfXdnQDlKmj0ivaHElucDu/dZao8cDa2E7Fg0g901CQ/Vo3KYdGCfS9cI4x7AJD6xiMDwrFugohggpKGip8sseplzNK2WFqMkv7XuX4Zc0D/c7OPH3zWd4LtfSz6EIztKNbyS8YEVp/GDYWUH4zXcmtQwZPZdI+uiXDNvCgZJ6gj4MV0t5b3e4XbaIOqdE8XcPl6J/i3Prp7NwJay28NXBvEtf0CjY0vJb10ZivgO6dxJy1JmfFRoTFnv2BXwmzGlbJfvc/maGJSFKD5gVrhYuDBkw3vIvvcIrAgSmPWrv4EkNcb2M= 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 Wed, May 21, 2025 at 11:53:37AM +0530, Bhupesh wrote: > Historically due to the 16-byte length of TASK_COMM_LEN, the > users of 'tsk->comm' are restricted to use a fixed-size target > buffer also of TASK_COMM_LEN for 'memcpy()' like use-cases. > > To fix the same, Linus suggested in [1] that we can add the > following union inside 'task_struct': > union { > char comm[TASK_COMM_LEN]; > char comm_ext[TASK_COMM_EXT_LEN]; > }; I remain unconvinced that this is at all safe. With the existing memcpy() and so many places using %s and task->comm, this feels very very risky to me. Can we just make it separate, instead of a union? Then we don't have to touch comm at all. > and then modify '__set_task_comm()' to pass 'tsk->comm_ext' > to the existing users. We can use set_task_comm() to set both still... -- Kees Cook