linux-hardening - [PATCH] exec: Distinguish in_execve from in

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Date: Wed, 24 Jan 2024 11:23:36 -0800
From: Kees Cook <keescook@...omium.org>
To: Kentaro Takeda <takedakn@...data.co.jp>
Cc: Kees Cook <keescook@...omium.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Eric Biederman <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Mike Christie <michael.christie@...cle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Mateusz Guzik <mjguzik@...il.com>,
	Nicholas Piggin <npiggin@...il.com>,
	Peng Zhang <zhangpeng.00@...edance.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] exec: Distinguish in_execve from in_exec

Just to help distinguish the fs->in_exec flag from the current->in_execve
flag, add comments in check_unsafe_exec() and copy_fs() for more
context. Also note that in_execve is only used by TOMOYO now.

Cc: Kentaro Takeda <takedakn@...data.co.jp>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Jan Kara <jack@...e.cz>
Cc: Eric Biederman <ebiederm@...ssion.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-mm@...ck.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/exec.c             | 1 +
 include/linux/sched.h | 2 +-
 kernel/fork.c         | 1 +
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index 39d773021fff..d179abb78a1c 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1633,6 +1633,7 @@ static void check_unsafe_exec(struct linux_binprm *bprm)
 	}
 	rcu_read_unlock();
 
+	/* "users" and "in_exec" locked for copy_fs() */
 	if (p->fs->users > n_fs)
 		bprm->unsafe |= LSM_UNSAFE_SHARE;
 	else
diff --git a/include/linux/sched.h b/include/linux/sched.h
index cdb8ea53c365..ffe8f618ab86 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -920,7 +920,7 @@ struct task_struct {
 	unsigned			sched_rt_mutex:1;
 #endif
 
-	/* Bit to tell LSMs we're in execve(): */
+	/* Bit to tell TOMOYO we're in execve(): */
 	unsigned			in_execve:1;
 	unsigned			in_iowait:1;
 #ifndef TIF_RESTORE_SIGMASK
diff --git a/kernel/fork.c b/kernel/fork.c
index 47ff3b35352e..0d944e92a43f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1748,6 +1748,7 @@ static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 	if (clone_flags & CLONE_FS) {
 		/* tsk->fs is already what we want */
 		spin_lock(&fs->lock);
+		/* "users" and "in_exec" locked for check_unsafe_exec() */
 		if (fs->in_exec) {
 			spin_unlock(&fs->lock);
 			return -EAGAIN;
-- 
2.34.1