Subject: Re: net: GPF in netlink_getsockbyportid

From: Florian Westphal <[email-masked]>
Date: Sat, 23 Jan 2016 20:25:02 +0100

Dmitry Vyukov <[email-masked]> wrote:

[ CC nf-devel, not sure if its nfnetlink fault or NETLINK_MMAP ]

> The following program causes GPF in netlink_getsockbyportid:
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <pthread.h>
> #include <stdint.h>
> #include <string.h>
> #include <sys/syscall.h>
> #include <unistd.h>
> 
> int main()
> {
>   syscall(SYS_mmap, 0x20000000ul, 0xe65000ul, 0x3ul, 0x32ul,
>                  0xfffffffffffffffful, 0x0ul);
>   int fd = syscall(SYS_socket, 0x10ul, 0x803ul, 0xcul, 0, 0, 0);
>   *(uint32_t*)0x20e64000 = (uint32_t)0x28;
>   *(uint32_t*)0x20e64004 = (uint32_t)0x10;
>   *(uint64_t*)0x20e64008 = (uint64_t)0x0;
>   *(uint64_t*)0x20e64010 = (uint64_t)0x3;
>   *(uint64_t*)0x20e64018 = (uint64_t)0xfff;
>   *(uint16_t*)0x20e64020 = (uint16_t)0x5;
>   syscall(SYS_write, fd, 0x20e64000ul, 0x28ul, 0, 0, 0);
>   return 0;
> }

CONFIG_NETLINK_MMAP and nfnetlink batching strike in unison :-/

root cause is in nfnetlink_rcv_batch():

296 replay:
297         status = 0;
298 
299         skb = netlink_skb_clone(oskb, GFP_KERNEL);

The clone op doesn't copy oskb->sk, so we oops in
__netlink_alloc_skb -> netlink_getsockbyportid() when nfnetlink_rcv_batch
tries to send netlink ack.