net/ipv6: use-after-free in ip6_dst_ifdown

[Andrey Konovalov]

Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

On commit 5ed02dbb497422bf225783f46e6eadd237d23d6b (4.12-rc3).

Unfortunately it's not reproducible.

==================================================================
BUG: KASAN: use-after-free in ip6_dst_ifdown+0x3cc/0x400 net/ipv6/route.c:422
Read of size 8 at addr ffff88006afa4ad8 by task syz-executor6/23554

CPU: 3 PID: 23554 Comm: syz-executor6 Not tainted 4.12.0-rc3+ #370
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x292/0x395 lib/dump_stack.c:52
 print_address_description+0x73/0x280 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x22b/0x340 mm/kasan/report.c:408
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429
 ip6_dst_ifdown+0x3cc/0x400 net/ipv6/route.c:422
 dst_ifdown+0x75/0x230 net/core/dst.c:439
 dst_dev_event+0xb1/0x230 net/core/dst.c:466
 notifier_call_chain+0x145/0x2e0 kernel/notifier.c:93
 __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
 call_netdevice_notifiers_info+0x51/0x90 net/core/dev.c:1649
 call_netdevice_notifiers net/core/dev.c:1665 [inline]
 __dev_notify_flags+0x1fd/0x320 net/core/dev.c:6640
 dev_change_flags+0xf5/0x140 net/core/dev.c:6671
 dev_ifsioc+0x62a/0x9f0 net/core/dev_ioctl.c:254
 dev_ioctl+0x249/0x1160 net/core/dev_ioctl.c:532
 sock_do_ioctl+0x94/0xb0 net/socket.c:913
 sock_ioctl+0x28f/0x440 net/socket.c:1004
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1bf/0x1660 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x446179
RSP: 002b:00007fd1da4bdc08 EFLAGS: 00000282 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000003220 RCX: 0000000000446179
RDX: 0000000020d34000 RSI: 0000000000008914 RDI: 0000000000000005
RBP: 00000000ffffffff R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000282 R12: 0000000000000005
R13: 0000000000000390 R14: 00000000006e1450 R15: 0000000000000000

Allocated by task 23235:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:617
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:555
 slab_post_alloc_hook mm/slab.h:456 [inline]
 slab_alloc_node mm/slub.c:2718 [inline]
 __kmalloc_node_track_caller+0x20d/0x350 mm/slub.c:4303
 __kmalloc_reserve.isra.32+0x41/0xd0 net/core/skbuff.c:138
 __alloc_skb+0x157/0x770 net/core/skbuff.c:231
 alloc_skb include/linux/skbuff.h:936 [inline]
 alloc_skb_with_frags+0x12e/0x780 net/core/skbuff.c:4690
 sock_alloc_send_pskb+0x804/0xa30 net/core/sock.c:2000
 tun_alloc_skb drivers/net/tun.c:1144 [inline]
 tun_get_user+0x91a/0x2e10 drivers/net/tun.c:1274
 tun_chr_write_iter+0xd8/0x190 drivers/net/tun.c:1365
 call_write_iter include/linux/fs.h:1734 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 __vfs_write+0x483/0x760 fs/read_write.c:510
 vfs_write+0x187/0x500 fs/read_write.c:558
 SYSC_write fs/read_write.c:605 [inline]
 SyS_write+0xfb/0x230 fs/read_write.c:597
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 23235:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525 [inline]
 kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:590
 slab_free_hook mm/slub.c:1357 [inline]
 slab_free_freelist_hook mm/slub.c:1379 [inline]
 slab_free mm/slub.c:2961 [inline]
 kfree+0xe8/0x2b0 mm/slub.c:3882
 skb_free_head+0x74/0xb0 net/core/skbuff.c:579
 skb_release_data+0x3ce/0x4a0 net/core/skbuff.c:610
 skb_release_all+0x4a/0x60 net/core/skbuff.c:669
 __kfree_skb+0x15/0x20 net/core/skbuff.c:683
 kfree_skb+0x16e/0x4e0 net/core/skbuff.c:704
 llc_rcv+0x5c7/0xed0 net/llc/llc_input.c:214
 __netif_receive_skb_core+0x1ad1/0x3400 net/core/dev.c:4216
 __netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4254
 netif_receive_skb_internal+0x240/0x1b20 net/core/dev.c:4416
 netif_receive_skb+0xae/0x3b0 net/core/dev.c:4440
 tun_rx_batched.isra.40+0x5e5/0x8c0 drivers/net/tun.c:1167
 tun_get_user+0x100d/0x2e10 drivers/net/tun.c:1339
 tun_chr_write_iter+0xd8/0x190 drivers/net/tun.c:1365
 call_write_iter include/linux/fs.h:1734 [inline]
 new_sync_write fs/read_write.c:497 [inline]
 __vfs_write+0x483/0x760 fs/read_write.c:510
 vfs_write+0x187/0x500 fs/read_write.c:558
 SYSC_write fs/read_write.c:605 [inline]
 SyS_write+0xfb/0x230 fs/read_write.c:597
 entry_SYSCALL_64_fastpath+0x1f/0xbe

The buggy address belongs to the object at ffff88006afa4ad8
 which belongs to the cache kmalloc-1024 of size 1024
The buggy address is located 0 bytes inside of
 1024-byte region [ffff88006afa4ad8, ffff88006afa4ed8)
The buggy address belongs to the page:
page:ffffea0001abe800 count:1 mapcount:0 mapping:          (null)
index:0x0 compound_mapcount: 0
flags: 0x500000000008100(slab|head)
raw: 0500000000008100 0000000000000000 0000000000000000 0000000100170017
raw: ffffea00017ef420 ffffea0001aaa420 ffff88003e80efc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88006afa4980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88006afa4a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88006afa4a80: fc fc fc fc fc fc fc fc fc fc fc fb fb fb fb fb
                                                    ^
 ffff88006afa4b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88006afa4b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================