linux-kernel - Re: + execve-must-clear-current-clear_child

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Message-ID: <20090731222959.GA8195@redhat.com>
Date:	Sat, 1 Aug 2009 00:29:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, eric.dumazet@...il.com,
	drepper@...hat.com, jens@...one.net, mingo@...e.hu,
	peterz@...radead.org, sonnyrao@...ibm.com, stable@...nel.org,
	tglx@...utronix.de, torvalds@...ux-foundation.org
Subject: Re: + execve-must-clear-current-clear_child_tid.patch added to -mm
	tree

> From: Eric Dumazet <eric.dumazet@...il.com>
>
> diff -puN fs/compat.c~execve-must-clear-current-clear_child_tid fs/compat.c
> --- a/fs/compat.c~execve-must-clear-current-clear_child_tid
> +++ a/fs/compat.c
> @@ -1550,6 +1550,7 @@ int compat_do_execve(char * filename,
>  	mutex_unlock(&current->cred_guard_mutex);
>  	acct_update_integrals(current);
>  	free_bprm(bprm);
> +	current->clear_child_tid = NULL;
>  	if (displaced)
>  		put_files_struct(displaced);
>  	return retval;
> diff -puN fs/exec.c~execve-must-clear-current-clear_child_tid fs/exec.c
> --- a/fs/exec.c~execve-must-clear-current-clear_child_tid
> +++ a/fs/exec.c
> @@ -1343,6 +1343,7 @@ int do_execve(char * filename,
>  	mutex_unlock(&current->cred_guard_mutex);
>  	acct_update_integrals(current);
>  	free_bprm(bprm);
> +	current->clear_child_tid = NULL;
>  	if (displaced)
>  		put_files_struct(displaced);
>  	return retval;

Perhaps it is better to change mm_release() ? It has to play with
->clear_child_tid anyway.

Oleg.

--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -568,18 +568,18 @@ void mm_release(struct task_struct *tsk,
 	 * the value intact in a core dump, and to save the unnecessary
 	 * trouble otherwise.  Userland only wants this done for a sys_exit.
 	 */
-	if (tsk->clear_child_tid
-	    && !(tsk->flags & PF_SIGNALED)
-	    && atomic_read(&mm->mm_users) > 1) {
-		u32 __user * tidptr = tsk->clear_child_tid;
+	if (tsk->clear_child_tid) {
+		if (!(tsk->flags & PF_SIGNALED) &&
+		    atomic_read(&mm->mm_users) > 1) {
+			/*
+			 * We don't check the error code - if userspace has
+			 * not set up a proper pointer then tough luck.
+			 */
+			put_user(0, tsk->clear_child_tid);
+			sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
+					1, NULL, NULL, 0);
+		}
 		tsk->clear_child_tid = NULL;
-
-		/*
-		 * We don't check the error code - if userspace has
-		 * not set up a proper pointer then tough luck.
-		 */
-		put_user(0, tidptr);
-		sys_futex(tidptr, FUTEX_WAKE, 1, NULL, NULL, 0);
 	}
 }
 

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