Re: KASAN: slab-out-of-bounds Read in _decode_session6

[Dmitry Vyukov <dvyukov@google.com>]

On Thu, Sep 6, 2018 at 7:27 PM, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Thu, Sep 06, 2018 at 12:00:26AM -0700, Eric Dumazet wrote:
>>
>>
>> On 09/05/2018 08:17 PM, syzbot wrote:
>> > syzbot has found a reproducer for the following crash on:
>> >
>> > HEAD commit:ááá b36fdc6853a3 Merge tag 'gpio-v4.19-2' of git://git.kernel...
>> > git tree:áááááá upstream
>> > console output: https://syzkaller.appspot.com/x/log.txt?x=164938d1400000
>> > kernel config:á https://syzkaller.appspot.com/x/.config?x=4c7e83258d6e0156
>> > dashboard link: https://syzkaller.appspot.com/bug?extid=acffccec848dc13fe459
>> > compiler:áááááá gcc (GCC) 8.0.1 20180413 (experimental)
>> > syz repro:ááááá https://syzkaller.appspot.com/x/repro.syz?x=115f172e400000
>> > C reproducer:áá https://syzkaller.appspot.com/x/repro.c?x=16399be1400000
>> >
>> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> > Reported-by: syzbot+acffccec848dc13fe459@syzkaller.appspotmail.com
>> >
>> > IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
>> > IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
>> > IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
>> > 8021q: adding VLAN 0 to HW filter on device team0
>> > ==================================================================
>> > BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
>> > Read of size 1 at addr ffff8801d4a67f07 by task syz-executor092/4673
>> >
>> > CPU: 1 PID: 4673 Comm: syz-executor092 Not tainted 4.19.0-rc2+ #223
>> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> > Call Trace:
>> > á__dump_stack lib/dump_stack.c:77 [inline]
>> > ádump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
>> > áprint_address_description+0x6c/0x20b mm/kasan/report.c:256
>> > ákasan_report_error mm/kasan/report.c:354 [inline]
>> > ákasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
>> > á__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
>> > á_decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
>> > á__xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
>> > áxfrm_decode_session include/net/xfrm.h:1232 [inline]
>> > ávti6_tnl_xmit+0x3fc/0x1bb1 net/ipv6/ip6_vti.c:542
>> > á__netdev_start_xmit include/linux/netdevice.h:4287 [inline]
>> > ánetdev_start_xmit include/linux/netdevice.h:4296 [inline]
>> > áxmit_one net/core/dev.c:3216 [inline]
>> > ádev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3232
>> > á__dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3802
>> > ádev_queue_xmit+0x17/0x20 net/core/dev.c:3835
>> > á__bpf_tx_skb net/core/filter.c:2012 [inline]
>> > á__bpf_redirect_common net/core/filter.c:2050 [inline]
>> > á__bpf_redirect+0x5b7/0xae0 net/core/filter.c:2057
>> > á____bpf_clone_redirect net/core/filter.c:2090 [inline]
>> > ábpf_clone_redirect+0x2f6/0x490 net/core/filter.c:2062
>> > ábpf_prog_c39d1ba309a769f7+0xe9e/0x1000
>> >
>> > Allocated by task 4673:
>> > ásave_stack+0x43/0xd0 mm/kasan/kasan.c:448
>> > áset_track mm/kasan/kasan.c:460 [inline]
>> > ákasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>> > á__do_kmalloc_node mm/slab.c:3682 [inline]
>> > á__kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3696
>> > á__kmalloc_reserve.isra.41+0x3a/0xe0 net/core/skbuff.c:137
>> > ápskb_expand_head+0x230/0x10e0 net/core/skbuff.c:1463
>> > áskb_ensure_writable+0x3dd/0x640 net/core/skbuff.c:5129
>> > á__bpf_try_make_writable net/core/filter.c:1633 [inline]
>> > ábpf_try_make_writable net/core/filter.c:1639 [inline]
>> > ábpf_try_make_head_writable net/core/filter.c:1647 [inline]
>> > á____bpf_clone_redirect net/core/filter.c:2084 [inline]
>> > ábpf_clone_redirect+0x14a/0x490 net/core/filter.c:2062
>> > ábpf_prog_c39d1ba309a769f7+0xe9e/0x1000
>> >
>> > Freed by task 3286:
>> > ásave_stack+0x43/0xd0 mm/kasan/kasan.c:448
>> > áset_track mm/kasan/kasan.c:460 [inline]
>> > á__kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>> > ákasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>> > á__cache_free mm/slab.c:3498 [inline]
>> > ákfree+0xd9/0x210 mm/slab.c:3813
>> > áload_elf_binary+0x2569/0x5610 fs/binfmt_elf.c:1118
>> > ásearch_binary_handler+0x17d/0x570 fs/exec.c:1653
>> > áexec_binprm fs/exec.c:1695 [inline]
>> > á__do_execve_file.isra.35+0x15ff/0x2460 fs/exec.c:1819
>> > ádo_execveat_common fs/exec.c:1866 [inline]
>> > ádo_execve fs/exec.c:1883 [inline]
>> > á__do_sys_execve fs/exec.c:1964 [inline]
>> > á__se_sys_execve fs/exec.c:1959 [inline]
>> > á__x64_sys_execve+0x8f/0xc0 fs/exec.c:1959
>> > ádo_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>> > áentry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > The buggy address belongs to the object at ffff8801d4a67d00
>> > áwhich belongs to the cache kmalloc-512 of size 512
>> > The buggy address is located 7 bytes to the right of
>> > á512-byte region [ffff8801d4a67d00, ffff8801d4a67f00)
>> > The buggy address belongs to the page:
>> > page:ffffea00075299c0 count:1 mapcount:0 mapping:ffff8801dac00940 index:0x0
>> > flags: 0x2fffc0000000100(slab)
>> > raw: 02fffc0000000100 ffffea0007529988 ffffea0007529a48 ffff8801dac00940
>> > raw: 0000000000000000 ffff8801d4a67080 0000000100000006 0000000000000000
>> > page dumped because: kasan: bad access detected
>> >
>> > Memory state around the buggy address:
>> > áffff8801d4a67e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> > áffff8801d4a67e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> >> ffff8801d4a67f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> > áááááááááááááááááá ^
>> > áffff8801d4a67f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> > áffff8801d4a68000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> > ==================================================================
>> >
>>
>>
>> What about :
>>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index aecdeba052d3f0ff3d4f0a33ec36891f9738052c..a662f59786bd0677850c1c60a2c92faa6fb6c5bb 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -2081,7 +2081,7 @@ BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
>>          * here, we need to free the just generated clone to unclone once
>>          * again.
>>          */
>> -       ret = bpf_try_make_head_writable(skb);
>> +       ret = bpf_try_make_head_writable(clone);
>
> This part is fine. I think the bug is in _decode_session6,

Eric, you arrived to roughly the same conclusion, right?

> but I have a hard time reproducing the issue, so will appreciate
> if somebody can test the following patch:

syzbot can:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches


> From 291f80f212461670d1e0140d06eee3071cf3e1ee Mon Sep 17 00:00:00 2001
> From: Alexei Starovoitov <ast@kernel.org>
> Date: Thu, 6 Sep 2018 10:23:29 -0700
> Subject: [PATCH] net/xfrm: fix out-of-bounds packet access
>
> BUG: KASAN: slab-out-of-bounds in _decode_session6+0x1331/0x14e0
> net/ipv6/xfrm6_policy.c:161
> Read of size 1 at addr ffff8801d882eec7 by task syz-executor1/6667
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
>   print_address_description+0x6c/0x20b mm/kasan/report.c:256
>   kasan_report_error mm/kasan/report.c:354 [inline]
>   kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
>   __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
>   _decode_session6+0x1331/0x14e0 net/ipv6/xfrm6_policy.c:161
>   __xfrm_decode_session+0x71/0x140 net/xfrm/xfrm_policy.c:2299
>   xfrm_decode_session include/net/xfrm.h:1232 [inline]
>   vti6_tnl_xmit+0x3c3/0x1bc1 net/ipv6/ip6_vti.c:542
>   __netdev_start_xmit include/linux/netdevice.h:4313 [inline]
>   netdev_start_xmit include/linux/netdevice.h:4322 [inline]
>   xmit_one net/core/dev.c:3217 [inline]
>   dev_hard_start_xmit+0x272/0xc10 net/core/dev.c:3233
>   __dev_queue_xmit+0x2ab2/0x3870 net/core/dev.c:3803
>   dev_queue_xmit+0x17/0x20 net/core/dev.c:3836
>
> Reported-by: syzbot+acffccec848dc13fe459@syzkaller.appspotmail.com
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  net/ipv6/xfrm6_policy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
> index ef3defaf43b9..d35bcf92969c 100644
> --- a/net/ipv6/xfrm6_policy.c
> +++ b/net/ipv6/xfrm6_policy.c
> @@ -146,8 +146,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
>         fl6->daddr = reverse ? hdr->saddr : hdr->daddr;
>         fl6->saddr = reverse ? hdr->daddr : hdr->saddr;
>
> -       while (nh + offset + 1 < skb->data ||
> -              pskb_may_pull(skb, nh + offset + 1 - skb->data)) {
> +       while (nh + offset + sizeof(*exthdr) < skb->data ||
> +              pskb_may_pull(skb, nh + offset + sizeof(*exthdr) - skb->data)) {
>                 nh = skb_network_header(skb);
>                 exthdr = (struct ipv6_opt_hdr *)(nh + offset);
>
> --
> 2.17.1
>
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