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
==================================================================
