linux-kernel - Re: net/kcm: WARNING in kcm_write

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Date:   Mon, 6 Feb 2017 13:43:31 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     David Miller <davem@...emloft.net>,
        Tom Herbert <tom@...bertland.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/kcm: WARNING in kcm_write_msgs

[resending as plain text]

Hello,

The following program triggers WARNING in kcm_write_msgs:

WARNING: CPU: 3 PID: 2936 at net/kcm/kcmsock.c:627
kcm_write_msgs+0x12e3/0x1b90 net/kcm/kcmsock.c:627
CPU: 3 PID: 2936 Comm: a.out Not tainted 4.10.0-rc6+ #209
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
 panic+0x1fb/0x412 kernel/panic.c:179
 __warn+0x1c4/0x1e0 kernel/panic.c:539
 warn_slowpath_null+0x2c/0x40 kernel/panic.c:582
 kcm_write_msgs+0x12e3/0x1b90 net/kcm/kcmsock.c:627
 kcm_sendmsg+0x163a/0x2200 net/kcm/kcmsock.c:1029
 sock_sendmsg_nosec net/socket.c:635 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:645
 sock_write_iter+0x326/0x600 net/socket.c:848
 new_sync_write fs/read_write.c:499 [inline]
 __vfs_write+0x483/0x740 fs/read_write.c:512
 vfs_write+0x187/0x530 fs/read_write.c:560
 SYSC_write fs/read_write.c:607 [inline]
 SyS_write+0xfb/0x230 fs/read_write.c:599
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x434c09
RSP: 002b:00007fff40f2d7b8 EFLAGS: 00000217 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000401960 RCX: 0000000000434c09
RDX: 0000000000000000 RSI: 00000000208aaf27 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 00007fff00000000
R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004002b0
R13: 0000000000401960 R14: 00000000004019f0 R15: 0000000000000000

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/in.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef __NR_bpf
#define __NR_bpf 321
#endif
#ifndef AF_KCM
#define AF_KCM 0x29
#endif

int main()
{
  syscall(__NR_mmap, 0x20000000ul, 0xfff000ul, 0x3ul, 0x32ul, -1, 0);
  int sock = socket(AF_INET6, SOCK_STREAM, IPPROTO_IP);
  (*(uint32_t*)0x20b4ffd0 = (uint32_t)0x1);
  (*(uint32_t*)0x20b4ffd4 = (uint32_t)0x2);
  (*(uint64_t*)0x20b4ffd8 = (uint64_t)0x20b4f000);
  (*(uint64_t*)0x20b4ffe0 = (uint64_t)0x2015a000);
  (*(uint32_t*)0x20b4ffe8 = (uint32_t)0x9);
  (*(uint32_t*)0x20b4ffec = (uint32_t)0x80);
  (*(uint64_t*)0x20b4fff0 = (uint64_t)0x20b4f000);
  (*(uint32_t*)0x20b4fff8 = (uint32_t)0x0);
  (*(uint8_t*)0x20b4f000 = (uint8_t)0xffffffffffffffb7);
  (*(uint8_t*)0x20b4f001 = (uint8_t)0x0);
  (*(uint16_t*)0x20b4f002 = (uint16_t)0x0);
  (*(uint32_t*)0x20b4f004 = (uint32_t)0x0);
  (*(uint8_t*)0x20b4f008 = (uint8_t)0x9595);
  (*(uint8_t*)0x20b4f009 = (uint8_t)0x0);
  (*(uint16_t*)0x20b4f00a = (uint16_t)0x0);
  (*(uint32_t*)0x20b4f00c = (uint32_t)0x0);
  (memcpy((void*)0x2015a000, "\x00\x8b", 2));
  int bpf = syscall(__NR_bpf, 0x5ul, 0x20b4ffd0ul, 0x30ul, 0, 0,
                          0, 0, 0, 0);
  int sock2 = syscall(__NR_socket, AF_KCM, 0x5ul, 0x0ul);
  (*(uint32_t*)0x20b5c000 = sock);
  (*(uint32_t*)0x20b5c004 = bpf);
  syscall(__NR_ioctl, sock2, 0x89e0ul, 0x20b5c000ul);
  syscall(__NR_write, sock2, 0x208aaf27ul, 0x0ul);
  return 0;
}


On commit a572a1b999489efb591287632279c6c9eca3e4ed