Commit 27e68f08 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

exec: Trivial cleanups for exec 

This is a continuation of my work to clean up exec so it's more
difficult problems are approachable.

The changes correct some comments, and moves the point_of_no_return
variable up to when the point_of_no_return actually occurs.

Eric W. Biederman (5):
      exec: Move the comment from above de_thread to above unshare_sighand
      exec: Fix spelling of search_binary_handler in a comment
      exec: Run sync_mm_rss before taking exec_update_mutex
      exec: Move handling of the point of no return to the top level
      exec: Set the point of no return sooner

 fs/exec.c | 46 ++++++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 22 deletions(-)

Link: https://lkml.kernel.org/r/87sgga6ze4.fsf@x220.int.ebiederm.org


Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parents b213c2dc 6834e0bb

fs/exec.c

+24 −22
Original line number Diff line number Diff line
@@ -1051,13 +1051,14 @@ static int exec_mmap(struct mm_struct *mm) 
	tsk = current;

	old_mm = current->mm;

	exec_mm_release(tsk, old_mm);

	if (old_mm)

		sync_mm_rss(old_mm);



	ret = mutex_lock_killable(&tsk->signal->exec_update_mutex);

	if (ret)

		return ret;



	if (old_mm) {

		sync_mm_rss(old_mm);

		/*

		 * Make sure that if there is a core dump in progress

		 * for the old mm, we get out and die instead of going
@@ -1093,12 +1094,6 @@ static int exec_mmap(struct mm_struct *mm) 
	return 0;

}



/*

 * This function makes sure the current process has its own signal table,

 * so that flush_signal_handlers can later reset the handlers without

 * disturbing other processes.  (Other processes might share the signal

 * table via the CLONE_SIGHAND option to clone().)

 */

static int de_thread(struct task_struct *tsk)

{

	struct signal_struct *sig = tsk->signal;
@@ -1240,6 +1235,12 @@ killed: 
}





/*

 * This function makes sure the current process has its own signal table,

 * so that flush_signal_handlers can later reset the handlers without

 * disturbing other processes.  (Other processes might share the signal

 * table via the CLONE_SIGHAND option to clone().)

 */

static int unshare_sighand(struct task_struct *me)

{

	struct sighand_struct *oldsighand = me->sighand;
@@ -1296,13 +1297,18 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec) 
 * Calling this is the point of no return. None of the failures will be

 * seen by userspace since either the process is already taking a fatal

 * signal (via de_thread() or coredump), or will have SEGV raised

 * (after exec_mmap()) by search_binary_handlers (see below).

 * (after exec_mmap()) by search_binary_handler (see below).

 */

int begin_new_exec(struct linux_binprm * bprm)

{

	struct task_struct *me = current;

	int retval;



	/*

	 * Ensure all future errors are fatal.

	 */

	bprm->point_of_no_return = true;



	/*

	 * Make this the only thread in the thread group.

	 */
@@ -1325,13 +1331,6 @@ int begin_new_exec(struct linux_binprm * bprm) 
	if (retval)

		goto out;



	/*

	 * With the new mm installed it is completely impossible to

	 * fail and return to the original process.  If anything from

	 * here on returns an error, the check in

	 * search_binary_handler() will SEGV current.

	 */

	bprm->point_of_no_return = true;

	bprm->mm = NULL;



#ifdef CONFIG_POSIX_TIMERS
@@ -1720,13 +1719,8 @@ int search_binary_handler(struct linux_binprm *bprm) 


		read_lock(&binfmt_lock);

		put_binfmt(fmt);

		if (retval < 0 && bprm->point_of_no_return) {

			/* we got to flush_old_exec() and failed after it */

			read_unlock(&binfmt_lock);

			force_sigsegv(SIGSEGV);

			return retval;

		}

		if (retval != -ENOEXEC || !bprm->file) {

		if (bprm->point_of_no_return || !bprm->file ||

		    (retval != -ENOEXEC)) {

			read_unlock(&binfmt_lock);

			return retval;

		}
@@ -1897,6 +1891,14 @@ static int __do_execve_file(int fd, struct filename *filename, 
	return retval;



out:

	/*

	 * If past the point of no return ensure the the code never

	 * returns to the userspace process.  Use an existing fatal

	 * signal if present otherwise terminate the process with

	 * SIGSEGV.

	 */

	if (bprm->point_of_no_return && !fatal_signal_pending(current))

		force_sigsegv(SIGSEGV);

	if (bprm->mm) {

		acct_arg_size(bprm, 0);

		mmput(bprm->mm);

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