Re: WARNING: refcount bug in sctp_wfree

[Qiujun Huang]

sctp_wfree
    ->refcount_sub_and_test(sizeof(struct sctp_chunk),
                                      &sk->sk_wmem_alloc)
sctp_wfree will sub sizeof(struct sctp_chunk) for every skb. So could
we add the extra size for gso segment ?



--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -398,7 +398,8 @@ static void sctp_packet_gso_append(struct sk_buff
*head, struct sk_buff *skb)
        head->truesize += skb->truesize;
        head->data_len += skb->len;
        head->len += skb->len;
-       refcount_add(skb->truesize, &head->sk->sk_wmem_alloc);
+       refcount_add(skb->truesize + sizeof(struct sctp_chunk),
+                               &head->sk->sk_wmem_alloc);

        __skb_header_release(skb);

On Tue, Mar 10, 2020 at 9:36 AM syzbot
<syzbot+cea71eec5d6de256d54d@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    2c523b34 Linux 5.6-rc5
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=155a5f29e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a5295e161cd85b82
> dashboard link: https://syzkaller.appspot.com/bug?extid=cea71eec5d6de256d54d
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=164b5181e00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=166dd70de00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+cea71eec5d6de256d54d@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ------------[ cut here ]------------
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 1 PID: 8668 at lib/refcount.c:28 refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 8668 Comm: syz-executor779 Not tainted 5.6.0-rc5-syzkaller #0
> 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+0x1e9/0x30e lib/dump_stack.c:118
>  panic+0x264/0x7a0 kernel/panic.c:221
>  __warn+0x209/0x210 kernel/panic.c:582
>  report_bug+0x1ac/0x2d0 lib/bug.c:195
>  fixup_bug arch/x86/kernel/traps.c:174 [inline]
>  do_error_trap+0xca/0x1c0 arch/x86/kernel/traps.c:267
>  do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
>  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
> RIP: 0010:refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28
> Code: c7 e4 ff d0 88 31 c0 e8 23 20 b3 fd 0f 0b eb 85 e8 8a 4a e0 fd c6 05 ff 70 b1 05 01 48 c7 c7 10 00 d1 88 31 c0 e8 05 20 b3 fd <0f> 0b e9 64 ff ff ff e8 69 4a e0 fd c6 05 df 70 b1 05 01 48 c7 c7
> RSP: 0018:ffffc90001f577d0 EFLAGS: 00010246
> RAX: 8c9c9070bbb4e500 RBX: 0000000000000003 RCX: ffff8880938a63c0
> RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
> RBP: 0000000000000003 R08: ffffffff815e16e6 R09: fffffbfff15db92a
> R10: fffffbfff15db92a R11: 0000000000000000 R12: dffffc0000000000
> R13: ffff88809de82000 R14: ffff8880a89237c0 R15: 1ffff11013be52b0
>  sctp_wfree+0x3b1/0x710 net/sctp/socket.c:9111
>  skb_release_head_state+0xfb/0x210 net/core/skbuff.c:651
>  skb_release_all net/core/skbuff.c:662 [inline]
>  __kfree_skb+0x22/0x1c0 net/core/skbuff.c:678
>  sctp_chunk_destroy net/sctp/sm_make_chunk.c:1454 [inline]
>  sctp_chunk_put+0x17b/0x200 net/sctp/sm_make_chunk.c:1481
>  __sctp_outq_teardown+0x80a/0x9d0 net/sctp/outqueue.c:257
>  sctp_association_free+0x21e/0x7c0 net/sctp/associola.c:339
>  sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:930 [inline]
>  sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1318 [inline]
>  sctp_side_effects net/sctp/sm_sideeffect.c:1185 [inline]
>  sctp_do_sm+0x3c01/0x5560 net/sctp/sm_sideeffect.c:1156
>  sctp_primitive_ABORT+0x93/0xc0 net/sctp/primitive.c:104
>  sctp_close+0x231/0x770 net/sctp/socket.c:1512
>  inet_release+0x135/0x180 net/ipv4/af_inet.c:427
>  __sock_release net/socket.c:605 [inline]
>  sock_close+0xd8/0x260 net/socket.c:1283
>  __fput+0x2d8/0x730 fs/file_table.c:280
>  task_work_run+0x176/0x1b0 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x5ef/0x1f80 kernel/exit.c:801
>  do_group_exit+0x15e/0x2c0 kernel/exit.c:899
>  __do_sys_exit_group+0x13/0x20 kernel/exit.c:910
>  __se_sys_exit_group+0x10/0x10 kernel/exit.c:908
>  __x64_sys_exit_group+0x37/0x40 kernel/exit.c:908
>  do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x43ef98
> Code: Bad RIP value.
> RSP: 002b:00007ffcc7e7c398 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ef98
> RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
> RBP: 00000000004be7a8 R08: 00000000000000e7 R09: ffffffffffffffd0
> R10: 000000002059aff8 R11: 0000000000000246 R12: 0000000000000001
> R13: 00000000006d01a0 R14: 0000000000000000 R15: 0000000000000000
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>
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> syzbot can test patches for this bug, for details see:
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