linux-kernel - Re: [PATCH 1/1] set wo_stat to an init value in do

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20111102145105.GA27394@redhat.com>
Date:	Wed, 2 Nov 2011 15:51:05 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	hank <pyu@...hat.com>
Cc:	tj@...nel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] set wo_stat to an init value in do_wait function

On 11/02, hank wrote:
>
> When all of the below conditions become true:
> 1 parent fork a child
> 2 parent ignore SIGCHLD signal
> 3 parent call waitpid function
> do_wait function won't touch the wo->stat variable.

Of course it doesn't, do_wait() fails and does nothing.

The parent ignores SIGCHLD. In this case waitpid(&status) acts as
if there are no children. Except it sleeps.

IOW,

> int main(int argc, char *argv[])
> {
>         int pid, child;
>         int status;
>         int *p;
> 
>         signal(SIGCHLD, SIG_IGN);
> 
>         child = fork();
>         if (child == 0) {
>                 sleep(1);
>                 exit(0);
>         } else if (child < 0) {
>                 perror("fork");
>                 exit(1);
>         } else {
>                 status = 0xa5a5;
>                 p = &status;
>                 printf("status addr: %p\n", p);
>                 pid = waitpid(-1, &status, WUNTRACED);
>                 printf("pid=%d status=0x%x\n", pid, status);
>                 exit(0);
>         }
>         return 0;
> }
> ========================================================
>
> After run this program, we can see the value of status is still
> 0xa5a5,so kernel do not touch this value.

Sure, this is correct.

> It may be dangerous. Because lots of programs such as 'su' don't set
> an init value for the variable 'status' when it call waitpid function,
> and after the waitpid function return, the program may check the value
> of 'status' to see the state of child.

Then this program is buggy. Once again, waitpid() fails. The program
shouldn't look at status at all.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/