Re: KASAN: invalid-free in tcf_exts_destroy

[Cong Wang]

On Sun, Mar 8, 2020 at 12:35 PM syzbot
<syzbot+dcc34d54d68ef7d2d53d@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    c2003765 Merge tag 'io_uring-5.6-2020-03-07' of git://git...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10cd2ae3e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4527d1e2fb19fd5c
> dashboard link: https://syzkaller.appspot.com/bug?extid=dcc34d54d68ef7d2d53d
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1561b01de00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15aad2f9e00000
>
> The bug was bisected to:
>
> commit 599be01ee567b61f4471ee8078870847d0a11e8e
> Author: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> Date:   Mon Feb 3 05:14:35 2020 +0000
>
>     net_sched: fix an OOB access in cls_tcindex
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10a275fde00000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=12a275fde00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a275fde00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+dcc34d54d68ef7d2d53d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 599be01ee567 ("net_sched: fix an OOB access in cls_tcindex")
>
> IPVS: ftp: loaded support on port[0] = 21
> ==================================================================
> BUG: KASAN: double-free or invalid-free in tcf_exts_destroy+0x62/0xc0 net/sched/cls_api.c:3002
>
> CPU: 1 PID: 9507 Comm: syz-executor467 Not tainted 5.6.0-rc4-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+0x188/0x20d lib/dump_stack.c:118
>  print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:374
>  kasan_report_invalid_free+0x61/0xa0 mm/kasan/report.c:468
>  __kasan_slab_free+0x129/0x140 mm/kasan/common.c:455
>  __cache_free mm/slab.c:3426 [inline]
>  kfree+0x109/0x2b0 mm/slab.c:3757
>  tcf_exts_destroy+0x62/0xc0 net/sched/cls_api.c:3002
>  tcf_exts_change+0xf4/0x150 net/sched/cls_api.c:3059
>  tcindex_set_parms+0xed8/0x1a00 net/sched/cls_tcindex.c:456

Looks like a consequence of "slab-out-of-bounds Write in tcindex_set_parms".

Thanks.