BUG: unable to handle kernel paging request in dummy_set_vf_spoofchk

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: aea8526e Linux 4.14.133
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12bd8fa4600000
kernel config: https://syzkaller.appspot.com/x/.config?x=5dfccef5a159766b
dashboard link: https://syzkaller.appspot.com/bug?extid=f3a94f2f3741010ca13e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16510cf0600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1416e894600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f3a94f...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
audit: type=1400 audit(1563654677.872:36): avc: denied { map } for
pid=6920 comm="syz-executor132" path="/root/syz-executor132896962"
dev="sda1" ino=16484 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
BUG: unable to handle kernel paging request at fffffffc40001810
IP: dummy_set_vf_spoofchk+0x7a/0xb0 /drivers/net/dummy.c:219
PGD 766d067 P4D 766d067 PUD 0
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 0 PID: 6920 Comm: syz-executor132 Not tainted 4.14.133 #28
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff8880978f8200 task.stack: ffff888084040000
RIP: 0010:dummy_set_vf_spoofchk+0x7a/0xb0 /drivers/net/dummy.c:219
RSP: 0018:ffff8880840472b0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: fffffffc40001800 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 00000000d8000100 RDI: fffffffc40001810
RBP: ffff8880840472c8 R08: 1ffff11010808e99 R09: ffff8880840474c8
R10: ffffed1010808ea5 R11: ffff88808404752f R12: ffff8880a19ee7c0
R13: 0000000000000000 R14: ffff888084047610 R15: ffff8880928ac368
FS: 0000000000726880(0000) GS:ffff8880aee00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffc40001810 CR3: 00000000969d1000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
do_setvfinfo /net/core/rtnetlink.c:1855 [inline]
do_setlink+0x1834/0x2d50 /net/core/rtnetlink.c:2135
rtnl_setlink+0x225/0x320 /net/core/rtnetlink.c:2303
rtnetlink_rcv_msg+0x3eb/0xb70 /net/core/rtnetlink.c:4285
netlink_rcv_skb+0x14f/0x3c0 /net/netlink/af_netlink.c:2432
rtnetlink_rcv+0x1d/0x30 /net/core/rtnetlink.c:4297
netlink_unicast_kernel /net/netlink/af_netlink.c:1286 [inline]
netlink_unicast+0x45d/0x780 /net/netlink/af_netlink.c:1312
netlink_sendmsg+0x7c4/0xc60 /net/netlink/af_netlink.c:1877
sock_sendmsg_nosec /net/socket.c:646 [inline]
sock_sendmsg+0xce/0x110 /net/socket.c:656
___sys_sendmsg+0x70a/0x840 /net/socket.c:2062
__sys_sendmsg+0xb9/0x140 /net/socket.c:2096
SYSC_sendmsg /net/socket.c:2107 [inline]
SyS_sendmsg+0x2d/0x50 /net/socket.c:2103
do_syscall_64+0x1e8/0x640 /arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x440259
RSP: 002b:00007ffe8d9eb298 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440259
RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401ae0
R13: 0000000000401b70 R14: 0000000000000000 R15: 0000000000000000
Code: 48 8d 1c d0 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 10 48 89 fa 48 c1
ea 03 0f b6 04 02 48 89 fa 83 e2 07 38 d0 7f 04 84 c0 75 16 <44> 88 6b 10
45 31 e4 e8 3a ad b8 fd 44 89 e0 5b 41 5c 41 5d 5d
RIP: dummy_set_vf_spoofchk+0x7a/0xb0 /drivers/net/dummy.c:219 RSP:
ffff8880840472b0
CR2: fffffffc40001810
---[ end trace b75eaf0c40c178af ]---


---
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[syzbot]

syzbot suspects this bug was fixed by commit:

commit 9ed49fc95f37a457d940324c033c20d85cefb930
Author: Dan Carpenter <dan.ca...@oracle.com>
Date: Wed Nov 20 12:34:38 2019 +0000

net: rtnetlink: prevent underflows in do_setvfinfo()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=118886fae00000
start commit: aea8526e Linux 4.14.133
git tree: linux-4.14.y

kernel config: https://syzkaller.appspot.com/x/.config?x=5dfccef5a159766b
dashboard link: https://syzkaller.appspot.com/bug?extid=f3a94f2f3741010ca13e

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16510cf0600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1416e894600000

If the result looks correct, please mark the bug fixed by replying with:

#syz fix: net: rtnetlink: prevent underflows in do_setvfinfo()

For information about bisection process see: https://goo.gl/tpsmEJ#bisection