Re: KASAN: use-after-free Read in bitmap_port_ext_cleanup

[Cong Wang]

On Fri, Jan 10, 2020 at 10:44 AM syzbot
<syzbot+4c3cc6dbe7259dbf9054@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    b07f636f Merge tag 'tpmdd-next-20200108' of git://git.infr..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16c03259e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=18698c0c240ba616
> dashboard link: https://syzkaller.appspot.com/bug?extid=4c3cc6dbe7259dbf9054
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10c365c6e00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117df9e1e00000
>
> The bug was bisected to:
>
> commit b9a1e627405d68d475a3c1f35e685ccfb5bbe668
> Author: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> Date:   Thu Jul 4 00:21:13 2019 +0000
>
>      hsr: implement dellink to clean up resources
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=118759e1e00000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=138759e1e00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=158759e1e00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+4c3cc6dbe7259dbf9054@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: b9a1e627405d ("hsr: implement dellink to clean up resources")
>
> ==================================================================
> BUG: KASAN: use-after-free in test_bit
> include/asm-generic/bitops/instrumented-non-atomic.h:110 [inline]
> BUG: KASAN: use-after-free in bitmap_port_ext_cleanup+0xe6/0x2a0
> net/netfilter/ipset/ip_set_bitmap_gen.h:51
> Read of size 8 at addr ffff8880a87a47c0 by task syz-executor559/9563
>
> CPU: 0 PID: 9563 Comm: syz-executor559 Not tainted 5.5.0-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+0x197/0x210 lib/dump_stack.c:118
>   print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
>   __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
>   kasan_report+0x12/0x20 mm/kasan/common.c:639
>   check_memory_region_inline mm/kasan/generic.c:185 [inline]
>   check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
>   __kasan_check_read+0x11/0x20 mm/kasan/common.c:95
>   test_bit include/asm-generic/bitops/instrumented-non-atomic.h:110 [inline]
>   bitmap_port_ext_cleanup+0xe6/0x2a0

map->members is freed by ip_set_free() right before using it in
mtype_ext_cleanup() again. So I think probably we just have to
move it down:

diff --git a/net/netfilter/ipset/ip_set_bitmap_gen.h
b/net/netfilter/ipset/ip_set_bitmap_gen.h
index 1abd6f0dc227..077a2cb65fcb 100644
--- a/net/netfilter/ipset/ip_set_bitmap_gen.h
+++ b/net/netfilter/ipset/ip_set_bitmap_gen.h
@@ -60,9 +60,9 @@ mtype_destroy(struct ip_set *set)
        if (SET_WITH_TIMEOUT(set))
                del_timer_sync(&map->gc);

-       ip_set_free(map->members);
        if (set->dsize && set->extensions & IPSET_EXT_DESTROY)
                mtype_ext_cleanup(set);
+       ip_set_free(map->members);
        ip_set_free(map);

        set->data = NULL;

Thanks.