net/kcm: WARNING in kcm_write_msgs

[Dmitry Vyukov]

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

[Dmitry Vyukov]

[resending as plain text]

[Cong Wang]

[...]
> syscall(__NR_write, sock2, 0x208aaf27ul, 0x0ul);

Looks like len == 0 case is not handled correctly in kcm_sendmsg().
The attached patch fixes it, but I am not sure if it is correct in all
cases yet, the logic is complicated.