BUG: unable to handle kernel paging request in dummy_set_vf_rate

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 01fd1694 Linux 4.14.141
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17a40b66600000
kernel config: https://syzkaller.appspot.com/x/.config?x=62c9b69e1b2adda9
dashboard link: https://syzkaller.appspot.com/bug?extid=520b63963f39a34c80ca
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16df9fae600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=108cefde600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+520b63...@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(1567725518.079:36): avc: denied { map } for
pid=6862 comm="syz-executor041" path="/root/syz-executor041712434"
dev="sda1" ino=16483 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 fffffffbb11e5804
IP: dummy_set_vf_rate+0x99/0x110 drivers/net/dummy.c:206
PGD 766d067 P4D 766d067 PUD 0
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 1 PID: 6862 Comm: syz-executor041 Not tainted 4.14.141 #37
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff88807ff36380 task.stack: ffff8880970e0000
RIP: 0010:dummy_set_vf_rate+0x99/0x110 drivers/net/dummy.c:206
RSP: 0018:ffff8880970e72a0 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: fffffffbb11e57f8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 00000000d20bee55 RDI: fffffffbb11e5804
RBP: ffff8880970e72c8 R08: 1ffff11012e1ce99 R09: ffff8880970e74c8
R10: ffffed1012e1cea5 R11: ffff8880970e752f R12: ffff8880a1a5cb40
R13: 0000000000000000 R14: 000000007005f108 R15: fffffffbb11e57f8
FS: 00000000008df880(0000) GS:ffff8880aef00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffbb11e5804 CR3: 0000000083b36000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
do_setvfinfo net/core/rtnetlink.c:1843 [inline]
do_setlink+0x1755/0x2d50 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/0x640 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: 0033:0x440239
RSP: 002b:00007ffd962d2be8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440239
RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401ac0
R13: 0000000000401b50 R14: 0000000000000000 R15: 0000000000000000
Code: df 49 8d 7f 0c 48 89 fa 48 c1 ea 03 0f b6 14 02 48 89 f8 83 e0 07 83
c0 01 38 d0 7c 04 84 d2 75 52 48 b8 00 00 00 00 00 fc ff df <66> 45 89 77
0c 49 03 9c 24 c0 0a 00 00 48 8d 7b 0e 48 89 fa 48
RIP: dummy_set_vf_rate+0x99/0x110 drivers/net/dummy.c:206 RSP:
ffff8880970e72a0
CR2: fffffffbb11e5804
---[ end trace 931eb1e77397f135 ]---


---
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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=17aba90ee00000
start commit: 01fd1694 Linux 4.14.141
git tree: linux-4.14.y

kernel config: https://syzkaller.appspot.com/x/.config?x=62c9b69e1b2adda9
dashboard link: https://syzkaller.appspot.com/bug?extid=520b63963f39a34c80ca

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16df9fae600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=108cefde600000

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