Messages in this thread | | | Date | Thu, 16 Oct 2014 19:37:33 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] kernel/kmod: fix use-after-free of the sub_info structure |
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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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