linux-kernel - Re: WARNING in __check_heap

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Date:   Tue, 7 Nov 2017 12:35:21 -0800
From:   Kees Cook <keescook@...omium.org>
To:     syzbot 
        <bot+2357afb48acb76780f3c18867ccfb7aa6fd6c4c9@...kaller.appspotmail.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        syzkaller-bugs@...glegroups.com, David Windsor <dave@...lcore.net>
Subject: Re: WARNING in __check_heap_object

On Tue, Nov 7, 2017 at 10:36 AM, syzbot
<bot+2357afb48acb76780f3c18867ccfb7aa6fd6c4c9@...kaller.appspotmail.com>
wrote:
> Hello,
>
> syzkaller hit the following crash on
> 5a3517e009e979f21977d362212b7729c5165d92
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
>
>

Please include the line _before_ the "cut here" (dumb, I know, but
that's where warnings show up...)

Found in the raw.log:

[   44.227177] unexpected usercopy without slab whitelist from SCTPv6
offset 1648 size 11

This means some part of the SCTPv6 slab was being poked into userspace
without a usercopy whitelist.

>  check_heap_object mm/usercopy.c:222 [inline]
>  __check_object_size+0x22c/0x4f0 mm/usercopy.c:248
>  check_object_size include/linux/thread_info.h:112 [inline]
>  check_copy_size include/linux/thread_info.h:143 [inline]
>  copy_to_user include/linux/uaccess.h:154 [inline]
>  sctp_getsockopt_events net/sctp/socket.c:4972 [inline]
>  sctp_getsockopt+0x2b90/0x70b0 net/sctp/socket.c:7012
>  sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2924
>  SYSC_getsockopt net/socket.c:1882 [inline]
>  SyS_getsockopt+0x178/0x340 net/socket.c:1864
>  entry_SYSCALL_64_fastpath+0x1f/0xbe

Looking at the SCTPv6 slab declaration, it seems David and I missed
the usercopy whitelist for the sctpv6_sock struct. I'll update the
usercopy whitelist patch with:

#syz fix: sctp: Define usercopy region in SCTP proto slab cache

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5fd83974c5cc..8ac85877c0e4 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -8492,6 +8492,10 @@ struct proto sctpv6_prot = {
        .unhash         = sctp_unhash,
        .get_port       = sctp_get_port,
        .obj_size       = sizeof(struct sctp6_sock),
+       .useroffset     = offsetof(struct sctp_sock, subscribe),
+       .usersize       = offsetof(struct sctp_sock, initmsg) -
+                               offsetof(struct sctp_sock, subscribe) +
+                               sizeof_field(struct sctp_sock, initmsg),
        .sysctl_mem     = sysctl_sctp_mem,
        .sysctl_rmem    = sysctl_sctp_rmem,
        .sysctl_wmem    = sysctl_sctp_wmem,

Thanks!

-Kees

-- 
Kees Cook
Pixel Security