Re: WARNING in __check_heap_object

[Dmitry Vyukov]

On Tue, Nov 7, 2017 at 9:35 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Tue, Nov 7, 2017 at 10:36 AM, syzbot
> <bot+2357afb48acb76780f3c18867ccfb7aa6fd6c4c9@xxxxxxxxxxxxxxxxxxxxxxxxx>
> 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, please also follow this part once the commit reaches any of
trees (title is settled):

> syzbot will keep track of this bug report.
> Once a fix for this bug is committed, please reply to this email with:
> #syz fix: exact-commit-title
> Note: all commands must start from beginning of the line.

This will greatly help to keep the whole process running and report
new bugs in future.

Thanks