linux-kernel - [PATCH 7/7] fork: Stop allowing kthreads to call execve

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Date:   Fri,  6 May 2022 09:15:12 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-arch@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 7/7] fork: Stop allowing kthreads to call execve

Now that kernel_execve is no longer called from kernel threads stop
supporting kernel threads calling kernel_execve.

Remove the code for converting a kthread to a normal thread in execve.

Document the restriction that kthreads may not call kernel_execve by
having kernel_execve fail if called by a kthread.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/exec.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 75eb6e0ee7b2..9c5260e74517 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1308,7 +1308,7 @@ int begin_new_exec(struct linux_binprm * bprm)
 	if (retval)
 		goto out_unlock;
 
-	me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
+	me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC |
 					PF_NOFREEZE | PF_NO_SETAFFINITY);
 	flush_thread();
 	me->personality &= ~bprm->per_clear;
@@ -1953,8 +1953,8 @@ int kernel_execve(const char *kernel_filename,
 	int fd = AT_FDCWD;
 	int retval;
 
-	if (WARN_ON_ONCE((current->flags & PF_KTHREAD) &&
-			(current->worker_private)))
+	/* It is non-sense for kernel threads to call execve */
+	if (WARN_ON_ONCE(current->flags & PF_KTHREAD))
 		return -EINVAL;
 
 	filename = getname_kernel(kernel_filename);
-- 
2.35.3