Re: net: GPF in netlink_getsockbyportid

On 01/23/2016 08:25 PM, Florian Westphal wrote:

Dmitry Vyukov [off-list ref] wrote:

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

quoted

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.

If indeed oskb is the mmap'ed netlink skb, then it's not even allowed
to call into skb_clone() as it would access skb shared info data that
can be controlled by the user space mmap buffer, iirc, we had that in
the past with nlmon where skb_clone() was accidentally used.