Commit c02e3f36 authored Sep 22, 2009 by Neil Horman Committed by Linus Torvalds Sep 23, 2009

kmod: fix race in usermodehelper code



The user mode helper code has a race in it.  call_usermodehelper_exec()
takes an allocated subprocess_info structure, which it passes to a
workqueue, and then passes it to a kernel thread which it creates, after
which it calls complete to signal to the caller of
call_usermodehelper_exec() that it can free the subprocess_info struct.

But since we use that structure in the created thread, we can't call
complete from __call_usermodehelper(), which is where we create the kernel
thread.  We need to call complete() from within the kernel thread and then
not use subprocess_info afterward in the case of UMH_WAIT_EXEC.  Tested
successfully by me.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1fd7317d

kernel/kmod.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -143,6 +143,7 @@ struct subprocess_info {
		static int ____call_usermodehelper(void *data)
		{
		struct subprocess_info *sub_info = data;
		enum umh_wait wait = sub_info->wait;
		int retval;

		BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
		@@ -184,9 +185,13 @@ static int ____call_usermodehelper(void *data)
		*/
		set_user_nice(current, 0);

		if (wait == UMH_WAIT_EXEC)
		complete(sub_info->complete);

		retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);

		/* Exec failed? */
		if (wait != UMH_WAIT_EXEC)
		sub_info->retval = retval;
		do_exit(0);
		}
		@@ -266,16 +271,14 @@ static void __call_usermodehelper(struct work_struct *work)

		switch (wait) {
		case UMH_NO_WAIT:
		case UMH_WAIT_EXEC:
		break;

		case UMH_WAIT_PROC:
		if (pid > 0)
		break;
		sub_info->retval = pid;
		/* FALLTHROUGH */

		case UMH_WAIT_EXEC:
		complete(sub_info->complete);
		break;
		}
		}