On 10/16, Martin Schwidefsky wrote:
>
> There is a use-after-free bug on the subprocess_info structure allocated
> by the user mode helper. In case do_execve() returns with an error
> ____call_usermodehelper() stores the error code to sub_info->retval,
> but sub_info can already have been freed.
Hmm, yes... do_execve() can fail after mm_release(). CLONE_VFORK doesn't
help in this case.
> @@ -242,13 +263,14 @@ static int ____call_usermodehelper(void *data)
> retval = do_execve(getname_kernel(sub_info->path),
> (const char __user *const __user *)sub_info->argv,
> (const char __user *const __user *)sub_info->envp);
> - if (!retval)
> - return 0;
> -
> - /* Exec failed? */
> -fail:
> +out:
> sub_info->retval = retval;
> - do_exit(0);
> + if (wait != UMH_WAIT_PROC)
> + /* For UMH_WAIT_PROC wait_for_helper calls umh_complete */
> + umh_complete(sub_info);
> + if (retval)
> + do_exit(0);
> + return 0;
> }
OK... I am wondering if __call_usermodehelper() still needs CLONE_VFORK
with this patch.
> @@ -588,7 +580,7 @@ int call_usermodehelper_exec(struct subprocess_info
> *sub_info, int wait)
> goto out;
> }
>
> - sub_info->complete = &done;
> + sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
This probably needs a comment, and the comment in umh_complete() should
be updated,
- we own sub_info, the UMH_KILLABLE caller has gone away.
+ we own sub_info, the UMH_KILLABLE caller has gone away
+ or the caller used UMH_NO_WAIT.
The patch looks correct at first glance. I'll try to re-read it later
once again.
Thanks!
Oleg.
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