Subject: KASAN: slab-out-of-bounds Read in sctp_inq_pop

From: syzbot <[email-masked]>
Date: Mon, 26 Aug 2019 10:14:08 -0700

Hello,

syzbot found the following crash on:

HEAD commit:    9733a7c6 Add linux-next specific files for 20190823
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=143ec11e600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f6c78a1438582bd1
dashboard link: https://syzkaller.appspot.com/bug?extid=3ca06c5cb35ee3fc1f89
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

==================================================================
BUG: KASAN: slab-out-of-bounds in sctp_inq_pop+0xafd/0xd80  
net/sctp/inqueue.c:201
Read of size 2 at addr ffff8880a4e37222 by task syz-executor.3/32407

CPU: 1 PID: 32407 Comm: syz-executor.3 Not tainted 5.3.0-rc5-next-20190823  
#72
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+0x172/0x1f0 lib/dump_stack.c:113
  print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
  __kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
  kasan_report+0x12/0x17 mm/kasan/common.c:610
  __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:130
  sctp_inq_pop+0xafd/0xd80 net/sctp/inqueue.c:201
  sctp_endpoint_bh_rcv+0x184/0x8d0 net/sctp/endpointola.c:335
  sctp_inq_push+0x1e4/0x280 net/sctp/inqueue.c:80
  sctp_rcv+0x2807/0x3590 net/sctp/input.c:256
  sctp6_rcv+0x17/0x30 net/sctp/ipv6.c:1049
  ip6_protocol_deliver_rcu+0x2fe/0x1660 net/ipv6/ip6_input.c:397
  ip6_input_finish+0x84/0x170 net/ipv6/ip6_input.c:438
  NF_HOOK include/linux/netfilter.h:305 [inline]
  NF_HOOK include/linux/netfilter.h:299 [inline]
  ip6_input+0xe4/0x3f0 net/ipv6/ip6_input.c:447
  dst_input include/net/dst.h:442 [inline]
  ip6_sublist_rcv_finish+0x98/0x1e0 net/ipv6/ip6_input.c:84
  ip6_list_rcv_finish net/ipv6/ip6_input.c:118 [inline]
  ip6_sublist_rcv+0x80c/0xcf0 net/ipv6/ip6_input.c:282
  ipv6_list_rcv+0x373/0x4b0 net/ipv6/ip6_input.c:316
  __netif_receive_skb_list_ptype net/core/dev.c:5049 [inline]
  __netif_receive_skb_list_core+0x1a2/0x9d0 net/core/dev.c:5087
  __netif_receive_skb_list net/core/dev.c:5149 [inline]
  netif_receive_skb_list_internal+0x7eb/0xe60 net/core/dev.c:5244
  gro_normal_list.part.0+0x1e/0xb0 net/core/dev.c:5757
  gro_normal_list net/core/dev.c:5755 [inline]
  gro_normal_one net/core/dev.c:5769 [inline]
  napi_frags_finish net/core/dev.c:5782 [inline]
  napi_gro_frags+0xa6a/0xea0 net/core/dev.c:5855
  tun_get_user+0x2e98/0x3fa0 drivers/net/tun.c:1974
  tun_chr_write_iter+0xbd/0x156 drivers/net/tun.c:2020
  call_write_iter include/linux/fs.h:1890 [inline]
  do_iter_readv_writev+0x5f8/0x8f0 fs/read_write.c:693
  do_iter_write fs/read_write.c:976 [inline]
  do_iter_write+0x17b/0x380 fs/read_write.c:957
  vfs_writev+0x1b3/0x2f0 fs/read_write.c:1021
  do_writev+0x15b/0x330 fs/read_write.c:1064
  __do_sys_writev fs/read_write.c:1137 [inline]
  __se_sys_writev fs/read_write.c:1134 [inline]
  __x64_sys_writev+0x75/0xb0 fs/read_write.c:1134
  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459731
Code: 75 14 b8 14 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 b9 fb ff c3 48  
83 ec 08 e8 fa 2c 00 00 48 89 04 24 b8 14 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 43 2d 00 00 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007fb4cd361ba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 000000000000002a RCX: 0000000000459731
RDX: 0000000000000001 RSI: 00007fb4cd361c00 RDI: 00000000000000f0
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 00007fb4cd3626d4
R13: 00000000004c87e3 R14: 00000000004df640 R15: 00000000ffffffff

Allocated by task 32407:
  save_stack+0x23/0x90 mm/kasan/common.c:69
  set_track mm/kasan/common.c:77 [inline]
  __kasan_kmalloc mm/kasan/common.c:486 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:459
  kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:494
  slab_post_alloc_hook mm/slab.h:584 [inline]
  slab_alloc mm/slab.c:3319 [inline]
  kmem_cache_alloc+0x121/0x710 mm/slab.c:3483
  __build_skb+0x26/0x70 net/core/skbuff.c:310
  __napi_alloc_skb+0x1d2/0x300 net/core/skbuff.c:523
  napi_alloc_skb include/linux/skbuff.h:2801 [inline]
  napi_get_frags net/core/dev.c:5742 [inline]
  napi_get_frags+0x65/0x140 net/core/dev.c:5737
  tun_napi_alloc_frags drivers/net/tun.c:1473 [inline]
  tun_get_user+0x16bd/0x3fa0 drivers/net/tun.c:1834
  tun_chr_write_iter+0xbd/0x156 drivers/net/tun.c:2020
  call_write_iter include/linux/fs.h:1890 [inline]
  do_iter_readv_writev+0x5f8/0x8f0 fs/read_write.c:693
  do_iter_write fs/read_write.c:976 [inline]
  do_iter_write+0x17b/0x380 fs/read_write.c:957
  vfs_writev+0x1b3/0x2f0 fs/read_write.c:1021
  do_writev+0x15b/0x330 fs/read_write.c:1064
  __do_sys_writev fs/read_write.c:1137 [inline]
  __se_sys_writev fs/read_write.c:1134 [inline]
  __x64_sys_writev+0x75/0xb0 fs/read_write.c:1134
  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 3891:
  save_stack+0x23/0x90 mm/kasan/common.c:69
  set_track mm/kasan/common.c:77 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:448
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:456
  __cache_free mm/slab.c:3425 [inline]
  kmem_cache_free+0x86/0x320 mm/slab.c:3693
  kfree_skbmem net/core/skbuff.c:623 [inline]
  kfree_skbmem+0xc5/0x150 net/core/skbuff.c:617
  __kfree_skb net/core/skbuff.c:680 [inline]
  consume_skb net/core/skbuff.c:838 [inline]
  consume_skb+0x103/0x3b0 net/core/skbuff.c:832
  skb_free_datagram+0x1b/0x100 net/core/datagram.c:328
  netlink_recvmsg+0x6c6/0xf50 net/netlink/af_netlink.c:1996
  sock_recvmsg_nosec net/socket.c:871 [inline]
  sock_recvmsg net/socket.c:889 [inline]
  sock_recvmsg+0xce/0x110 net/socket.c:885
  ___sys_recvmsg+0x271/0x5a0 net/socket.c:2480
  __sys_recvmsg+0x102/0x1d0 net/socket.c:2537
  __do_sys_recvmsg net/socket.c:2547 [inline]
  __se_sys_recvmsg net/socket.c:2544 [inline]
  __x64_sys_recvmsg+0x78/0xb0 net/socket.c:2544
  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a4e37140
  which belongs to the cache skbuff_head_cache of size 224
The buggy address is located 2 bytes to the right of
  224-byte region [ffff8880a4e37140, ffff8880a4e37220)
The buggy address belongs to the page:
page:ffffea0002938dc0 refcount:1 mapcount:0 mapping:ffff88821b6a3a80  
index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea000257fa88 ffffea00023a2008 ffff88821b6a3a80
raw: 0000000000000000 ffff8880a4e37000 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8880a4e37100: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
  ffff8880a4e37180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8880a4e37200: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
                                ^
  ffff8880a4e37280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a4e37300: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================

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