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

From: syzbot <[email-masked]>
Date: Thu, 23 Jul 2020 11:12:23 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    8c26c87b Merge tag 'sound-5.8-rc7' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=128af5ef100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f87a5e4232fdb267
dashboard link: https://syzkaller.appspot.com/bug?extid=d702fd2351989927037c
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1567cae8900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=150631b4900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

==================================================================
BUG: KASAN: use-after-free in vlan_dev_get_iflink+0x5f/0x70 net/8021q/vlan_dev.c:767
Read of size 4 at addr ffff888094a76100 by task syz-executor015/9454

CPU: 1 PID: 9454 Comm: syz-executor015 Not tainted 5.8.0-rc6-syzkaller #0
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+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 vlan_dev_get_iflink+0x5f/0x70 net/8021q/vlan_dev.c:767
 dev_get_iflink+0x73/0xe0 net/core/dev.c:814
 rfc2863_policy+0x243/0x2e0 net/core/link_watch.c:41
 linkwatch_do_dev+0x2a/0x180 net/core/link_watch.c:160
 linkwatch_forget_dev+0x16a/0x200 net/core/link_watch.c:237
 netdev_wait_allrefs net/core/dev.c:9678 [inline]
 netdev_run_todo+0x258/0xac0 net/core/dev.c:9774
 rtnl_unlock net/core/rtnetlink.c:112 [inline]
 rtnetlink_rcv_msg+0x45b/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: 0033:0x446cf9
Code: Bad RIP value.
RSP: 002b:00007f4a27e29d98 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dbc78 RCX: 0000000000446cf9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000006
RBP: 00000000006dbc70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc7c
R13: 0000000040000000 R14: 0000001000000000 R15: 0705001000000048

Allocated by task 9440:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
 kmalloc_node include/linux/slab.h:578 [inline]
 kvmalloc_node+0x61/0xf0 mm/util.c:574
 kvmalloc include/linux/mm.h:753 [inline]
 kvzalloc include/linux/mm.h:761 [inline]
 alloc_netdev_mqs+0x97/0xdc0 net/core/dev.c:9938
 rtnl_create_link+0x219/0xad0 net/core/rtnetlink.c:3067
 __rtnl_newlink+0xfa0/0x1730 net/core/rtnetlink.c:3329
 rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3397
 rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5460
 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

Freed by task 9461:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 kasan_set_free_info mm/kasan/common.c:316 [inline]
 __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x103/0x2c0 mm/slab.c:3757
 kvfree+0x42/0x50 mm/util.c:603
 device_release+0x71/0x200 drivers/base/core.c:1579
 kobject_cleanup lib/kobject.c:693 [inline]
 kobject_release lib/kobject.c:722 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1c0/0x270 lib/kobject.c:739
 netdev_run_todo+0x765/0xac0 net/core/dev.c:9797
 rtnl_unlock net/core/rtnetlink.c:112 [inline]
 rtnetlink_rcv_msg+0x45b/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

The buggy address belongs to the object at ffff888094a76000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 256 bytes inside of
 4096-byte region [ffff888094a76000, ffff888094a77000)
The buggy address belongs to the page:
page:ffffea0002529d80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 head:ffffea0002529d80 order:1 compound_mapcount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea000251fe88 ffffea0002375c88 ffff8880aa002000
raw: 0000000000000000 ffff888094a76000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888094a76000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888094a76080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888094a76100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888094a76180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888094a76200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

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