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b=lRIW9KGHcqL0Fmk+5ttu/lxjwJbU/eFI84L7Hj2MdW1ul6fOEUBmOnNycwc827Q4i LJEsZJ4GrO/oavqNwFPm9QRw9JUObG/+JjzR4v93D3Z/GX86s3koBwvt/aib1W/GAM 3RexJjMDXqALCzOv+OU2x4dAPCS7pO0Y31VMtBcJ6qNYaNPH6sRFA3Mnsp8YtAIEBs z3FgN22qFgnMhUL3M9Kn9FiIpuoW6nQxO/phd+Q1+C0IteuDAAlQ0Y242fixPEdh1m DqLjhm17PE65XTYxL6aNBrQ0qbhAUzoCYsp2B2mMVvwDSjijsYmA9fI8vyAmTLKO38 kzpv0dDDyGK6w== Date: Thu, 24 Jul 2025 16:38:02 -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 3/3] include: Set tsk->comm length to 64 bytes Message-ID: <202507241634.C0346AC@keescook> References: <20250724123612.206110-1-bhupesh@igalia.com> <20250724123612.206110-4-bhupesh@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250724123612.206110-4-bhupesh@igalia.com> X-Rspamd-Queue-Id: 584A240005 X-Stat-Signature: ia4gsf3po35rtfw5c4n9yksnji6rpedp X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1753400284-8869 X-HE-Meta: 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 eUSH+cBY jHkAUjceJ6dgsrF0SJzFOnHWnEqjcnuM1PfxVxkNU0DyN+294PrL/hIP9fr9wr370tmxvNAKworKzfCd4zcojVgxG1rwxv5ouyU+Q1B3Z/pnBHyprfSZp8Ez8PWM1liz5JSdfYGiTC07IYR+KltYKAekuNWMTp4VN8qtpeKgb+33QjnjbPdTOF3J+hZw3icRWYPLlUGv1Ouzo1qZwPkAyJ0M+/eOwqnGWCGmM28mJeUMpT+vZgA6tNH+cy1ZZ1F9Y+GZwl2hk6Uvm5Dtf+EymhOiPaH9Ml0GG/F0HHtN+m8Rnkv3+wWipIlRRRJZ1AX+Ffqt7JBOdotKu0GY5UtkQckg+gWXuzj9mqaSdc7/VrvmH+mRTqbjyMmm1FOBhLqgHesxSaBYv57iz6LEt51A7I0jcREII0bw1y4ga 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 06:06:12PM +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, we now use a 64-byte TASK_COMM_EXT_LEN and > set the comm element inside 'task_struct' to the same length: > struct task_struct { > ..... > char comm[TASK_COMM_EXT_LEN]; > ..... > }; > > where TASK_COMM_EXT_LEN is 64-bytes. > > Now, in order to maintain existing ABI, we ensure that: > > - Existing users of 'get_task_comm'/ 'set_task_comm' will get 'tsk->comm' > truncated to a maximum of 'TASK_COMM_LEN' (16-bytes) to maintain ABI, > - New / Modified users of 'get_task_comm'/ 'set_task_comm' will get > 'tsk->comm' supported up to the maximum of 'TASK_COMM_EXT_LEN' (64-bytes). > > Note, that the existing users have not been modified to migrate to > 'TASK_COMM_EXT_LEN', in case they have hard-coded expectations of > dealing with only a 'TASK_COMM_LEN' long 'tsk->comm'. > > Signed-off-by: Bhupesh > --- > include/linux/sched.h | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 8bbd03f1b978..b6abb759292c 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -317,6 +317,7 @@ struct user_event_mm; > */ > enum { > TASK_COMM_LEN = 16, > + TASK_COMM_EXT_LEN = 64, > }; > > extern void sched_tick(void); > @@ -1159,7 +1160,7 @@ struct task_struct { > * - logic inside set_task_comm() will ensure it is always NUL-terminated and > * zero-padded > */ > - char comm[TASK_COMM_LEN]; > + char comm[TASK_COMM_EXT_LEN]; > > struct nameidata *nameidata; > > @@ -1954,7 +1955,7 @@ extern void kick_process(struct task_struct *tsk); > > extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec); > #define set_task_comm(tsk, from) ({ \ > - BUILD_BUG_ON(sizeof(from) != TASK_COMM_LEN); \ > + BUILD_BUG_ON(sizeof(from) < TASK_COMM_LEN); \ > __set_task_comm(tsk, from, false); \ > }) > > @@ -1974,6 +1975,10 @@ extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec > #define get_task_comm(buf, tsk) ({ \ > BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \ > strscpy_pad(buf, (tsk)->comm); \ > + if ((sizeof(buf)) == TASK_COMM_LEN) \ > + buf[TASK_COMM_LEN - 1] = '\0'; \ > + else \ > + buf[TASK_COMM_EXT_LEN - 1] = '\0'; \ strscpy_pad() will already make sure buf is NUL-terminated, so I don't see why there is a need for explicit final byte termination? (And even if we do need it, then it should just be buf[sizeof(buf) - 1] otherwise using a buf that is < TASK_COMM_EXT_LEN but > TASK_COMM_LEN will have a spurious NUL byte write beyond its buffer.) -- Kees Cook