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b=bJxNpYzI0tSBL5Fd29YBqt79bpQuPHJNkgU4HWnA1ipoJVQQZT04gS6GlTXUNKCwy 3rcJdbbtZ1g5w0e2VEc4waAwbeLBmoazhpr56/B+rqY2+09YmOSm3SK7rhCp68n+Lr R3G+z+RTFDsgCo2N5w5VeWUNyc9m/eisSE7A4xc0VMJ4DNcGiXJgqitCxfSFpKrmqM lpbZ7wkGZQgQbumA5YCATMoACJohz5/36tiJVZuB6+isXlsuNB3XJ80QqhbjYcEkut buu/3pAZLr+gH0MryQDouwotjTR47MnGIKmSAPS7JraCOv/Tq9a4zA0NG4H1RtoHU7 yE9OI/ry0AzBg== Date: Thu, 3 Apr 2025 09:30:22 -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 Subject: Re: [PATCH v2 1/3] exec: Dynamically allocate memory to store task's full name Message-ID: <202504030924.50896AD12@keescook> References: <20250331121820.455916-1-bhupesh@igalia.com> <20250331121820.455916-2-bhupesh@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250331121820.455916-2-bhupesh@igalia.com> X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8C63316000D X-Stat-Signature: bjcz6xxk6fkr49aqfykm611wn8wkoh6d X-HE-Tag: 1743697827-877110 X-HE-Meta: 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 /YX00ElN hzcEZNoTF1Ta+YG6Us2NY0KWerJnv3El64aOqMnDpN8ry5RNGxIKI6UO7NHoMiRPzwTXRN4Sz5EnrKhE73TT6ByzSj1ZIl6n4q2d72feHlRHywYmuqMqEpWuKwzzIldwN3lM2Md0XxxRUakh4wkVJ6oLNqX/PY2QPWyITP4pgcNcBTPnOdZ4IvOJmwNGpeNNfo/XKbiVjelNDxUB2RbLAsmD6sm6NygM2GiBERbyUEedJIIsQHHGH4PAAEBmZ1mmOw5z0v32ZzS2o376i+shHNxNC79ajndhKYo2DuVUhHiiHDxLzkbDbJ363q86y53JGgswd7Y9kHAeqwj82xauO3IXh9dvxiaAZOh5aillM2Th/FJDdUSP1/N/nmE/qt4sNRHRt 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 Mon, Mar 31, 2025 at 05:48:18PM +0530, Bhupesh wrote: > Provide a parallel implementation for get_task_comm() called > get_task_full_name() which allows the dynamically allocated > and filled-in task's full name to be passed to interested > users such as 'gdb'. > > Currently while running 'gdb', the 'task->comm' value of a long > task name is truncated due to the limitation of TASK_COMM_LEN. > > For example using gdb to debug a simple app currently which generate > threads with long task names: > # gdb ./threadnames -ex "run info thread" -ex "detach" -ex "quit" > log > # cat log > > NameThatIsTooLo > > This patch does not touch 'TASK_COMM_LEN' at all, i.e. > 'TASK_COMM_LEN' and the 16-byte design remains untouched. Which means > that all the legacy / existing ABI, continue to work as before using > '/proc/$pid/task/$tid/comm'. > > This patch only adds a parallel, dynamically-allocated > 'task->full_name' which can be used by interested users > via '/proc/$pid/task/$tid/full_name'. > > After this change, gdb is able to show full name of the task: > # gdb ./threadnames -ex "run info thread" -ex "detach" -ex "quit" > log > # cat log > > NameThatIsTooLongForComm[4662] > > Signed-off-by: Bhupesh > --- > fs/exec.c | 21 ++++++++++++++++++--- > include/linux/sched.h | 9 +++++++++ > 2 files changed, 27 insertions(+), 3 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index f45859ad13ac..4219d77a519c 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1208,6 +1208,9 @@ int begin_new_exec(struct linux_binprm * bprm) > { > struct task_struct *me = current; > int retval; > + va_list args; > + char *name; > + const char *fmt; > > /* Once we are committed compute the creds */ > retval = bprm_creds_from_file(bprm); > @@ -1348,11 +1351,22 @@ int begin_new_exec(struct linux_binprm * bprm) > * detecting a concurrent rename and just want a terminated name. > */ > rcu_read_lock(); > - __set_task_comm(me, smp_load_acquire(&bprm->file->f_path.dentry->d_name.name), > - true); > + fmt = smp_load_acquire(&bprm->file->f_path.dentry->d_name.name); > + name = kvasprintf(GFP_KERNEL, fmt, args); > + if (!name) > + return -ENOMEM; > + > + me->full_name = name; > + __set_task_comm(me, fmt, true); I don't want to add new allocations to the default exec path unless we absolutely must. In the original proposal this was about setting thread names (after exec), and I think that'll be fine. > rcu_read_unlock(); > } else { > - __set_task_comm(me, kbasename(bprm->filename), true); > + fmt = kbasename(bprm->filename); > + name = kvasprintf(GFP_KERNEL, fmt, args); > + if (!name) > + return -ENOMEM; > + > + me->full_name = name; > + __set_task_comm(me, fmt, true); > } I think we can just set me->full_name = me->comm by default. > > /* An exec changes our domain. We are no longer part of the thread > @@ -1399,6 +1413,7 @@ int begin_new_exec(struct linux_binprm * bprm) > return 0; > > out_unlock: > + kfree(me->full_name); > up_write(&me->signal->exec_update_lock); > if (!bprm->cred) > mutex_unlock(&me->signal->cred_guard_mutex); > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 56ddeb37b5cd..053b52606652 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1166,6 +1166,9 @@ struct task_struct { > */ > char comm[TASK_COMM_LEN]; > > + /* To store the full name if task comm is truncated. */ > + char *full_name; > + > struct nameidata *nameidata; > > #ifdef CONFIG_SYSVIPC > @@ -2007,6 +2010,12 @@ extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec > buf; \ > }) > > +#define get_task_full_name(buf, buf_size, tsk) ({ \ > + BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \ > + strscpy_pad(buf, (tsk)->full_name, buf_size); \ > + buf; \ > +}) I think it should be possible to just switch get_task_comm() to use (tsk)->full_name. -- Kees Cook