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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>
This commit is contained in:
Neil Horman 2009-09-22 16:43:36 -07:00 committed by Linus Torvalds
parent 1fd7317d02
commit c02e3f361c
1 changed files with 8 additions and 5 deletions
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13
kernel/kmod.c
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@ -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);
@ -184,10 +185,14 @@ 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? */
sub_info->retval = retval;
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;
}
}