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Date:   Sat, 14 Mar 2020 10:51:35 +0800
From:   Qiujun Huang <anenbupt@...il.com>
To:     syzbot <syzbot+cea71eec5d6de256d54d@...kaller.appspotmail.com>,
        vyasevich@...il.com
Cc:     davem@...emloft.net, kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux-sctp@...r.kernel.org, marcelo.leitner@...il.com,
        netdev@...r.kernel.org, nhorman@...driver.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING: refcount bug in sctp_wfree

For geo segment sob, we shouldn't subtract the sizeof(struct
scup_chunk) in scup_wfree.

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index fed26a1e9518..e0cc5d7c88fb 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -9085,7 +9085,9 @@ static void sctp_wfree(struct sk_buff *skb)
        sk_mem_uncharge(sk, skb->truesize);
        sk->sk_wmem_queued -= skb->truesize + sizeof(struct sctp_chunk);
        asoc->sndbuf_used -= skb->truesize + sizeof(struct sctp_chunk);
-       WARN_ON(refcount_sub_and_test(sizeof(struct sctp_chunk),
+
+       if (skb_is_gso(skb))
+               WARN_ON(refcount_sub_and_test(sizeof(struct sctp_chunk),
                                      &sk->sk_wmem_alloc));

On Wed, Mar 11, 2020 at 11:00 PM Qiujun Huang <anenbupt@...il.com> wrote:
>
> 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@...kaller.appspotmail.com> 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@...kaller.appspotmail.com
> >
> > ------------[ 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@...glegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches

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