On Thu, Dec 06, 2018 at 11:36:08AM +0100, Alexander Potapenko wrote:

On Wed, Dec 5, 2018 at 8:31 PM syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot found the following crash on:

HEAD commit:    fffec98ae2a6 net: proper support for CONFIG_GENERIC_CSUM o..
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=12e84a47400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=56b48b46dafe4516
dashboard link: https://syzkaller.appspot.com/bug?extid=ad5d327e6936a2e284be
compiler:       clang version 8.0.0 (trunk 343298)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=103cd225400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ad5d327e6936a2e284be@syzkaller.appspotmail.com

8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KMSAN: kernel-infoleak in _copy_to_user+0x19a/0x230 lib/usercopy.c:33
CPU: 1 PID: 8164 Comm: syz-executor2 Not tainted 4.20.0-rc3+ #95
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x32d/0x480 lib/dump_stack.c:113
  kmsan_report+0x12c/0x290 mm/kmsan/kmsan.c:683
  kmsan_internal_check_memory+0x32a/0xa50 mm/kmsan/kmsan.c:743
  kmsan_copy_to_user+0x78/0xd0 mm/kmsan/kmsan_hooks.c:634
  _copy_to_user+0x19a/0x230 lib/usercopy.c:33
  copy_to_user include/linux/uaccess.h:183 [inline]
  sctp_getsockopt_local_addrs net/sctp/socket.c:5998 [inline]
  sctp_getsockopt+0x15248/0x186f0 net/sctp/socket.c:7477
  sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
  __sys_getsockopt+0x489/0x550 net/socket.c:1939
  __do_sys_getsockopt net/socket.c:1950 [inline]
  __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
  __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
  do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
  entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f4991886c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000457569
RDX: 000000000000006d RSI: 0000000000000084 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000020000140 R09: 0000000000000000
R10: 0000000020001100 R11: 0000000000000246 R12: 00007f49918876d4
R13: 00000000004c7d88 R14: 00000000004ce348 R15: 00000000ffffffff

Uninit was stored to memory at:
  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
  kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
  kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
  kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
  kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
  __msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
  sctp_copy_laddrs net/sctp/socket.c:5901 [inline]
  sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
  sctp_getsockopt+0x14f41/0x186f0 net/sctp/socket.c:7477
  sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
  __sys_getsockopt+0x489/0x550 net/socket.c:1939
  __do_sys_getsockopt net/socket.c:1950 [inline]
  __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
  __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
  do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
  entry_SYSCALL_64_after_hwframe+0x63/0xe7

Uninit was stored to memory at:
  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
  kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
  kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
  kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
  kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
  __msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
  sctp_copy_laddrs net/sctp/socket.c:5890 [inline]
  sctp_getsockopt_local_addrs net/sctp/socket.c:5967 [inline]
  sctp_getsockopt+0x14de8/0x186f0 net/sctp/socket.c:7477
  sock_common_getsockopt+0x13f/0x180 net/core/sock.c:2937
  __sys_getsockopt+0x489/0x550 net/socket.c:1939
  __do_sys_getsockopt net/socket.c:1950 [inline]
  __se_sys_getsockopt+0xe1/0x100 net/socket.c:1947
  __x64_sys_getsockopt+0x62/0x80 net/socket.c:1947
  do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
  entry_SYSCALL_64_after_hwframe+0x63/0xe7

Uninit was created at:
  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
  kmsan_internal_poison_shadow+0x6d/0x130 mm/kmsan/kmsan.c:170
  kmsan_kmalloc+0xa1/0x100 mm/kmsan/kmsan_hooks.c:186
  __kmalloc+0x14c/0x4d0 mm/slub.c:3825
  kmalloc include/linux/slab.h:551 [inline]
  sctp_inet6addr_event+0x60e/0xbd0 net/sctp/ipv6.c:100
  notifier_call_chain kernel/notifier.c:93 [inline]
  __atomic_notifier_call_chain kernel/notifier.c:183 [inline]
  atomic_notifier_call_chain+0x13d/0x240 kernel/notifier.c:193
  inet6addr_notifier_call_chain+0x76/0x90 net/ipv6/addrconf_core.c:107
  ipv6_add_addr+0x2597/0x2890 net/ipv6/addrconf.c:1115
  inet6_addr_add+0xc86/0x1c10 net/ipv6/addrconf.c:2912
  inet6_rtm_newaddr+0x167e/0x3d20 net/ipv6/addrconf.c:4750
  rtnetlink_rcv_msg+0x1148/0x1540 net/core/rtnetlink.c:4947
  netlink_rcv_skb+0x394/0x640 net/netlink/af_netlink.c:2477
  rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:4965
  netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
  netlink_unicast+0x1699/0x1740 net/netlink/af_netlink.c:1336
  netlink_sendmsg+0x13c7/0x1440 net/netlink/af_netlink.c:1917
  sock_sendmsg_nosec net/socket.c:621 [inline]
  sock_sendmsg net/socket.c:631 [inline]
  ___sys_sendmsg+0xe3b/0x1240 net/socket.c:2116
  __sys_sendmsg net/socket.c:2154 [inline]
  __do_sys_sendmsg net/socket.c:2163 [inline]
  __se_sys_sendmsg+0x305/0x460 net/socket.c:2161
  __x64_sys_sendmsg+0x4a/0x70 net/socket.c:2161
  do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
  entry_SYSCALL_64_after_hwframe+0x63/0xe7

Bytes 32-35 of 2100 are uninitialized
Memory access of size 2100 starts at ffff888185d8b000
Data copied to user address 0000000020001108
==================================================================

When a network device goes up and sctp_inetaddr_event() is called, it
allocates a partially initialized struct sctp_sockaddr_entry to hold
the newly created address.
The attached reproducer can be then used to read up to 8 uninit bytes
for each of the local addresses.
I guess the devices aren't created so often that this can pose any
security risk, but we probably still need to allocate this structure
with __GFP_ZERO.

Agree. Thanks Alexander.
Looks like this is the last/only place left with this issue.

quoted

---
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See https://goo.gl/tpsmEJ for more information about syzbot.
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-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
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#ifndef DUMP_BUF_H
#define DUMP_BUF_H

#ifndef DUMP_MIN_STRLEN
#define DUMP_MIN_STRLEN 1
#endif

#ifndef DUMP_PARALLEL
#define DUMP_PARALLEL 0
#endif

#ifndef DUMP_PRINT_BUF_ADDR
#define DUMP_PRINT_BUF_ADDR 0
#endif

#ifndef DUMP_PRINT_HEX
#define DUMP_PRINT_HEX 0
#endif

#ifndef DUMP_PRINT_STRING
#define DUMP_PRINT_STRING 0
#endif

#if DUMP_PARALLEL
pthread_mutex_t out_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif

void dump_buf(unsigned char *buf, int len) {
  int i, nz = 0;
  for (i = 0; i < len; i++) {
    if (buf[i]) {
      nz = 1;
      break;
    }
  }
  if (!nz) {
    // The buffer is empty.
    return;
  } else {
#if DUMP_PARALLEL
    pthread_mutex_lock(&out_mutex);
#endif
#if DUMP_PRINT_BUF_ADDR
    fprintf(stderr, "nonempty buffer at %p\n", buf);
#endif
#if DUMP_PRINT_HEX
    for (i=0; i < len; i++) {
      if (buf[i]) {
        fprintf(stderr, "buf[%d]: %x (%p)\n", i, buf[i], *(void**)&buf[i]);
      }
    }
#endif // DUMP_PRINT_HEX
#if DUMP_PARALLEL
    pthread_mutex_unlock(&out_mutex);
#endif
  }
#if DUMP_PARALLEL
  pthread_mutex_lock(&out_mutex);
#endif
#if DUMP_PRINT_STRING
  for (i = 0; i < len; i++) {
    if (buf[i]) {
      int str_len = strlen(&buf[i]);
      // Short string pieces are too boring.
      if (str_len >= DUMP_MIN_STRLEN) {
        unsigned char *c;
        for (c = &buf[i]; c < &buf[i + str_len]; c++) {
          if ((*c > 127) || ((*c < 32) && (*c != 10) && (*c != 13)))  {
            *c = ' ';
            continue;
          }
        }
        // Dump the buffer.
        fprintf(stderr, "%s\n", &buf[i]);
      }
      i += str_len;
    }
  }
#endif // DUMP_PRINT_STRING
#if DUMP_PARALLEL
  pthread_mutex_unlock(&out_mutex);
#endif
}

#endif

#include <stdio.h>
#include <pthread.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <unistd.h>

#define DUMP_PARALLEL 1
#define DUMP_PRINT_BUF_ADDR 1
#define DUMP_PRINT_STRING 1
#define DUMP_PRINT_HEX 1
#include "dump_buf.h"

void *setsockopt_fn(void *arg) {
  int sock = (int)arg;
  struct sockaddr addr;
  memset(&addr, 0, sizeof(addr));
  addr.sa_family = 2;
  addr.sa_data[2] = 0xac;
  addr.sa_data[3] = 0x14;
  addr.sa_data[4] = 0x14;
  setsockopt(sock, 0x84, 0x6e, &addr, 0x10);
}

#define BUFLEN (0x2c2)
void *getsockopt_fn(void *arg) {
  int sock = (int)arg;
  char buf[BUFLEN];
  memset(buf, 0, BUFLEN);
  int socklen = BUFLEN;
  getsockopt(sock, 0x84, /*SCTP_GET_LOCAL_ADDRS*/0x6d, buf, &socklen);
  dump_buf(&(buf[8]), 32);
}

void do_work(int sock) {
  pthread_t t1, t2;
  for (int i = 0; i < 10; i++) {
    pthread_create(&t1, NULL, getsockopt_fn, (void*)sock);
    pthread_create(&t2, NULL, setsockopt_fn, (void*)sock);
    usleep(100);
  }
}

int main(int argc, char *argv[]) {
  int res;
  int pid = fork();
  if (pid == 0) {
    int sock = socket(0x2, 0x1, 0x84);
    do_work(sock);
  }
  sleep(10);
  return 0;
}