Subject: Re: KASAN: use-after-free Read in vlan_dev_get_iflink

From: syzbot <[email-masked]>
Date: Thu, 23 Jul 2020 14:30:07 -0700

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in vlan_get_link_net

general protection fault, probably for non-canonical address 0xdffffc00000000b3: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000598-0x000000000000059f]
CPU: 1 PID: 8207 Comm: syz-executor.3 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:read_pnet include/net/net_namespace.h:330 [inline]
RIP: 0010:dev_net include/linux/netdevice.h:2261 [inline]
RIP: 0010:vlan_get_link_net+0x46/0x70 net/8021q/vlan_netlink.c:279
Code: fa 48 c1 ea 03 80 3c 02 00 75 2e 48 8b 9b 70 0c 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d bb 98 05 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 10 48 8b 83 98 05 00 00 5b c3 e8 86 1f 63 fa eb cb
RSP: 0018:ffffc90004706eb8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff888092c85230
RDX: 00000000000000b3 RSI: ffffffff874ffe39 RDI: 0000000000000598
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8a7b8647
R10: 0000000000000000 R11: 0000000000000000 R12: ffffc90004706f80
R13: 0000000000000030 R14: ffff8880930ba900 R15: ffff8880930cc000
FS:  00007f4a9113a700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005643b6ad2140 CR3: 000000009335e000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 rtnl_fill_link_netnsid net/core/rtnetlink.c:1569 [inline]
 rtnl_fill_ifinfo+0x1bc5/0x3c40 net/core/rtnetlink.c:1758
 rtmsg_ifinfo_build_skb+0xcd/0x1a0 net/core/rtnetlink.c:3706
 rollback_registered_many+0xb7d/0xf60 net/core/dev.c:8972
 unregister_netdevice_many.part.0+0x1a/0x2f0 net/core/dev.c:10113
 unregister_netdevice_many+0x36/0x50 net/core/dev.c:10112
 __rtnl_newlink+0x13bd/0x1750 net/core/rtnetlink.c:3381
 rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3398
 rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5461
 netlink_rcv_skb+0x15a/0x430 net/netlink/af_netlink.c:2469
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2352
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2406
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45c1f9
Code: Bad RIP value.
RSP: 002b:00007f4a91139c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000002b580 RCX: 000000000045c1f9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000006
RBP: 000000000078bfe0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000078bfac
R13: 00007ffc004cce8f R14: 00007f4a9113a9c0 R15: 000000000078bfac
Modules linked in:
---[ end trace e42f7b565341dee6 ]---
RIP: 0010:read_pnet include/net/net_namespace.h:330 [inline]
RIP: 0010:dev_net include/linux/netdevice.h:2261 [inline]
RIP: 0010:vlan_get_link_net+0x46/0x70 net/8021q/vlan_netlink.c:279
Code: fa 48 c1 ea 03 80 3c 02 00 75 2e 48 8b 9b 70 0c 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d bb 98 05 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 10 48 8b 83 98 05 00 00 5b c3 e8 86 1f 63 fa eb cb
RSP: 0018:ffffc90004706eb8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff888092c85230
RDX: 00000000000000b3 RSI: ffffffff874ffe39 RDI: 0000000000000598
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8a7b8647
R10: 0000000000000000 R11: 0000000000000000 R12: ffffc90004706f80
R13: 0000000000000030 R14: ffff8880930ba900 R15: ffff8880930cc000
FS:  00007f4a9113a700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005643b6ad2140 CR3: 000000009335e000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Tested on:

commit:         9506a941 net: fix a race condition in dev_get_iflink()
git tree:       https://github.com/congwang/linux.git net
console output: https://syzkaller.appspot.com/x/log.txt?x=158bd540900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dddbcb5a9f4192db
dashboard link: https://syzkaller.appspot.com/bug?extid=d702fd2351989927037c
compiler:       gcc (GCC) 10.1.0-syz 20200507