Date:   Mon, 25 Mar 2019 01:35:54 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     syzbot <syzbot+580be3953ed99133804f@...kaller.appspotmail.com>
Cc:     Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        LKML <linux-kernel@...r.kernel.org>,
        Li RongQing <lirongqing@...du.com>, magnus.karlsson@...el.com,
        maximmi@...lanox.com, netdev <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Song Liu <songliubraving@...com>,
        syzkaller-bugs@...glegroups.com, vincent.whitchurch@...s.com,
        Willem de Bruijn <willemb@...gle.com>,
        Yonghong Song <yhs@...com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: KASAN: use-after-free Write in skb_release_data (2)

On Mon, Mar 25, 2019 at 1:19 AM syzbot
<syzbot+580be3953ed99133804f@...kaller.appspotmail.com> wrote:
>
> syzbot has bisected this bug to:
>
> commit 472c2e07eef045145bc1493cc94a01c87140780a
> Author: Eric Dumazet <edumazet@...gle.com>
> Date:   Fri Mar 22 15:56:39 2019 +0000
>
>      tcp: add one skb cache for tx
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17abf52b200000
> start commit:   68cc2999 Merge branch 'devlink-small-spring-cleanup'
> git tree:       net-next
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=146bf52b200000
> console output: https://syzkaller.appspot.com/x/log.txt?x=106bf52b200000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9ab5bbbbf283c99a
> dashboard link: https://syzkaller.appspot.com/bug?extid=580be3953ed99133804f
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=123a3d3b200000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d34f93200000
>
> Reported-by: syzbot+580be3953ed99133804f@...kaller.appspotmail.com
> Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

This bisection makes no sense, the original bug report was in in
October last year.

This was :

Hello,

syzbot found the following crash on:

HEAD commit:    e40a826a6cbc qed: Add support for virtual link.
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=168954a5400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7e7e2279c0020d5f
dashboard link: https://syzkaller.appspot.com/bug?extid=580be3953ed99133804f
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+580be3953ed99133804f@...kaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in atomic_sub_return
include/asm-generic/atomic-instrumented.h:305 [inline]
BUG: KASAN: use-after-free in skb_release_data+0x1a3/0x880 net/core/skbuff.c:559
Write of size 4 at addr ffff8801d8cb4120 by task syz-executor0/8395

CPU: 0 PID: 8395 Comm: syz-executor0 Not tainted 4.19.0-rc6+ #254
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+0x1c4/0x2b4 lib/dump_stack.c:113
 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
 atomic_sub_return include/asm-generic/atomic-instrumented.h:305 [inline]
 skb_release_data+0x1a3/0x880 net/core/skbuff.c:559
 skb_release_all+0x4a/0x60 net/core/skbuff.c:627
 __kfree_skb net/core/skbuff.c:641 [inline]
 kfree_skb+0x1bb/0x580 net/core/skbuff.c:659
 sit_tunnel_xmit+0x173/0x30d0 net/ipv6/sit.c:1044
 __netdev_start_xmit include/linux/netdevice.h:4328 [inline]
 netdev_start_xmit include/linux/netdevice.h:4337 [inline]
 xmit_one net/core/dev.c:3219 [inline]
 dev_hard_start_xmit+0x295/0xc90 net/core/dev.c:3235
 __dev_queue_xmit+0x2f0d/0x3950 net/core/dev.c:3805
 dev_queue_xmit+0x17/0x20 net/core/dev.c:3838
 packet_sendmsg_spkt+0xf44/0x16f0 net/packet/af_packet.c:1975
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457519
Code: 1d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 0f 83 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f2a52d30c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457519
RDX: 0000000000000000 RSI: 00000000200003c0 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2a52d316d4
R13: 00000000004c34d5 R14: 00000000004d52c8 R15: 00000000ffffffff

Allocated by task 8395:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
 __do_kmalloc_node mm/slab.c:3682 [inline]
 __kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3696
 __kmalloc_reserve.isra.39+0x41/0xe0 net/core/skbuff.c:137
 __alloc_skb+0x155/0x770 net/core/skbuff.c:205
 alloc_skb include/linux/skbuff.h:997 [inline]
 sock_wmalloc+0x16d/0x1f0 net/core/sock.c:1934
 packet_sendmsg_spkt+0x48a/0x16f0 net/packet/af_packet.c:1922
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8395:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
 __cache_free mm/slab.c:3498 [inline]
 kfree+0xcf/0x230 mm/slab.c:3813
 skb_free_head+0x99/0xc0 net/core/skbuff.c:550
 skb_release_data+0x6a4/0x880 net/core/skbuff.c:570
 skb_release_all+0x4a/0x60 net/core/skbuff.c:627
 __kfree_skb net/core/skbuff.c:641 [inline]
 consume_skb+0x1ae/0x570 net/core/skbuff.c:701
 packet_rcv+0x172/0x1820 net/packet/af_packet.c:2139
 dev_queue_xmit_nit+0x8ae/0xb30 net/core/dev.c:2020
 xmit_one net/core/dev.c:3215 [inline]
 dev_hard_start_xmit+0x186/0xc90 net/core/dev.c:3235
 __dev_queue_xmit+0x2f0d/0x3950 net/core/dev.c:3805
 dev_queue_xmit+0x17/0x20 net/core/dev.c:3838
 packet_sendmsg_spkt+0xf44/0x16f0 net/packet/af_packet.c:1975
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d8cb4040
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 224 bytes inside of
 512-byte region [ffff8801d8cb4040, ffff8801d8cb4240)
The buggy address belongs to the page:
page:ffffea0007632d00 count:1 mapcount:0 mapping:ffff8801da800940
index:0xffff8801d8cb42c0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea00070baf08 ffffea000736a788 ffff8801da800940
raw: ffff8801d8cb42c0 ffff8801d8cb4040 0000000100000005 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d8cb4000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff8801d8cb4080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

ffff8801d8cb4100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                               ^
 ffff8801d8cb4180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d8cb4200: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


---
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:
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