==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:71 [inline]
BUG: KASAN: use-after-free in atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
BUG: KASAN: use-after-free in refcount_read include/linux/refcount.h:147 [inline]
BUG: KASAN: use-after-free in skb_unref include/linux/skbuff.h:1131 [inline]
BUG: KASAN: use-after-free in consume_skb+0x3c/0x250 net/core/skbuff.c:926
Read of size 4 at addr ffff88810d94b4ac by task syz.8.9796/2958
CPU: 0 PID: 2958 Comm: syz.8.9796 Tainted: G W 5.15.167-syzkaller-android13-5.15.167_r00 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x151/0x1c0 lib/dump_stack.c:106
print_address_description+0x87/0x3b0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:427 [inline]
kasan_report+0x179/0x1c0 mm/kasan/report.c:444
kasan_check_range+0x293/0x2a0 mm/kasan/generic.c:189
__kasan_check_read+0x11/0x20 mm/kasan/shadow.c:31
instrument_atomic_read include/linux/instrumented.h:71 [inline]
atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
refcount_read include/linux/refcount.h:147 [inline]
skb_unref include/linux/skbuff.h:1131 [inline]
consume_skb+0x3c/0x250 net/core/skbuff.c:926
__sk_msg_free+0x2dd/0x370 net/core/skmsg.c:205
sk_msg_free net/core/skmsg.c:218 [inline]
__sk_psock_purge_ingress_msg net/core/skmsg.c:769 [inline]
__sk_psock_zap_ingress net/core/skmsg.c:787 [inline]
sk_psock_stop+0x44c/0x4d0 net/core/skmsg.c:805
sk_psock_drop+0x219/0x310 net/core/skmsg.c:844
sk_psock_put include/linux/skmsg.h:458 [inline]
sock_map_unref+0x48f/0x4d0 net/core/sock_map.c:183
__sock_map_delete net/core/sock_map.c:425 [inline]
sock_map_delete_from_link net/core/sock_map.c:438 [inline]
sock_map_unlink net/core/sock_map.c:1496 [inline]
sock_map_remove_links+0x41c/0x650 net/core/sock_map.c:1511
sock_map_close+0x114/0x530 net/core/sock_map.c:1548
unix_release+0x82/0xc0 net/unix/af_unix.c:936
__sock_release net/socket.c:649 [inline]
sock_close+0xdf/0x270 net/socket.c:1336
__fput+0x228/0x8c0 fs/file_table.c:280
____fput+0x15/0x20 fs/file_table.c:308
task_work_run+0x129/0x190 kernel/task_work.c:188
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop+0xc4/0xe0 kernel/entry/common.c:181
exit_to_user_mode_prepare+0x5a/0xa0 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x26/0x160 kernel/entry/common.c:307
do_syscall_64+0x47/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f6fa3170719
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff3a406de8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f6fa3329a80 RCX: 00007f6fa3170719
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f6fa3329a80 R08: 0000000000000000 R09: 00007fff3a4070df
R10: 000000000003fd90 R11: 0000000000000246 R12: 0000000000221780
R13: 00007fff3a406ef0 R14: 0000000000000032 R15: ffffffffffffffff
Allocated by task 2959:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:45 [inline]
set_alloc_info mm/kasan/common.c:433 [inline]
__kasan_slab_alloc+0xb1/0xe0 mm/kasan/common.c:466
kasan_slab_alloc include/linux/kasan.h:217 [inline]
slab_post_alloc_hook+0x53/0x2c0 mm/slab.h:550
slab_alloc_node mm/slub.c:3240 [inline]
slab_alloc mm/slub.c:3248 [inline]
kmem_cache_alloc+0xf5/0x200 mm/slub.c:3253
skb_clone+0x1d1/0x360 net/core/skbuff.c:1547
sk_psock_verdict_recv+0x53/0x840 net/core/skmsg.c:1183
unix_read_sock+0x132/0x370 net/unix/af_unix.c:2428
sk_psock_verdict_data_ready+0x147/0x1a0 net/core/skmsg.c:1226
unix_dgram_sendmsg+0x15fa/0x2090 net/unix/af_unix.c:1942
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
____sys_sendmsg+0x59e/0x8f0 net/socket.c:2431
___sys_sendmsg+0x252/0x2e0 net/socket.c:2485
__sys_sendmsg net/socket.c:2514 [inline]
__do_sys_sendmsg net/socket.c:2523 [inline]
__se_sys_sendmsg+0x19a/0x260 net/socket.c:2521
__x64_sys_sendmsg+0x7b/0x90 net/socket.c:2521
x64_sys_call+0x16a/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Freed by task 20:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:45
kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
____kasan_slab_free+0x126/0x160 mm/kasan/common.c:365
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
kasan_slab_free include/linux/kasan.h:193 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook+0xbd/0x190 mm/slub.c:1749
slab_free mm/slub.c:3519 [inline]
kmem_cache_free+0x116/0x2e0 mm/slub.c:3535
kfree_skbmem+0x104/0x170
__kfree_skb net/core/skbuff.c:758 [inline]
kfree_skb_reason net/core/skbuff.c:778 [inline]
kfree_skb+0xc2/0x360 net/core/skbuff.c:792
sock_drop include/linux/skmsg.h:312 [inline]
sk_psock_backlog+0xc21/0xd90 net/core/skmsg.c:682
process_one_work+0x6bb/0xc10 kernel/workqueue.c:2325
worker_thread+0xad5/0x12a0 kernel/workqueue.c:2472
kthread+0x421/0x510 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
The buggy address belongs to the object at ffff88810d94b3c0
which belongs to the cache skbuff_head_cache of size 248
The buggy address is located 236 bytes inside of
248-byte region [ffff88810d94b3c0, ffff88810d94b4b8)
The buggy address belongs to the page:
page:ffffea00043652c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10d94b
flags: 0x4000000000000200(slab|zone=1)
raw: 4000000000000200 0000000000000000 0000000b00000001 ffff8881081b2d80
raw: 0000000000000000 00000000800c000c 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY), pid 0, ts 18866660400, free_ts 18193916984
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x1a3/0x1b0 mm/page_alloc.c:2605
prep_new_page+0x1b/0x110 mm/page_alloc.c:2611
get_page_from_freelist+0x3550/0x35d0 mm/page_alloc.c:4485
__alloc_pages+0x27e/0x8f0 mm/page_alloc.c:5779
allocate_slab mm/slub.c:1932 [inline]
new_slab+0x9a/0x4e0 mm/slub.c:1995
___slab_alloc+0x39e/0x830 mm/slub.c:3028
__slab_alloc+0x4a/0x90 mm/slub.c:3115
slab_alloc_node mm/slub.c:3206 [inline]
slab_alloc mm/slub.c:3248 [inline]
kmem_cache_alloc+0x134/0x200 mm/slub.c:3253
__build_skb+0x2a/0x300 net/core/skbuff.c:242
build_skb+0x25/0x1f0 net/core/skbuff.c:259
page_to_skb+0x154/0xb40 drivers/net/virtio_net.c:440
receive_mergeable drivers/net/virtio_net.c:1070 [inline]
receive_buf+0xed6/0x57d0 drivers/net/virtio_net.c:1180
virtnet_receive drivers/net/virtio_net.c:1472 [inline]
virtnet_poll+0x615/0x1250 drivers/net/virtio_net.c:1585
__napi_poll+0xc4/0x5a0 net/core/dev.c:7042
napi_poll net/core/dev.c:7109 [inline]
net_rx_action+0x47d/0xc50 net/core/dev.c:7199
handle_softirqs+0x25e/0x5c0 kernel/softirq.c:565
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1472 [inline]
free_pcp_prepare mm/page_alloc.c:1544 [inline]
free_unref_page_prepare+0x7c8/0x7d0 mm/page_alloc.c:3534
free_unref_page_list+0x14b/0xa60 mm/page_alloc.c:3671
release_pages+0x1310/0x1370 mm/swap.c:1009
free_pages_and_swap_cache+0x8a/0xa0 mm/swap_state.c:320
tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:240 [inline]
tlb_flush_mmu mm/mmu_gather.c:247 [inline]
tlb_finish_mmu+0x177/0x320 mm/mmu_gather.c:338
exit_mmap+0x40d/0x940 mm/mmap.c:3218
__mmput+0x95/0x310 kernel/fork.c:1179
mmput+0x5b/0x170 kernel/fork.c:1202
exit_mm kernel/exit.c:554 [inline]
do_exit+0xb9c/0x2ca0 kernel/exit.c:867
do_group_exit+0x141/0x310 kernel/exit.c:1002
__do_sys_exit_group kernel/exit.c:1013 [inline]
__se_sys_exit_group kernel/exit.c:1011 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1011
x64_sys_call+0x610/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Memory state around the buggy address:
ffff88810d94b380: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
ffff88810d94b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810d94b480: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc
^
ffff88810d94b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810d94b580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc
==================================================================
==================================================================
BUG: KASAN: double-free or invalid-free in slab_free mm/slub.c:3519 [inline]
BUG: KASAN: double-free or invalid-free in kmem_cache_free+0x116/0x2e0 mm/slub.c:3535
CPU: 0 PID: 2958 Comm: syz.8.9796 Tainted: G B W 5.15.167-syzkaller-android13-5.15.167_r00 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x151/0x1c0 lib/dump_stack.c:106
print_address_description+0x87/0x3b0 mm/kasan/report.c:248
kasan_report_invalid_free+0x6b/0xa0 mm/kasan/report.c:370
____kasan_slab_free+0x13e/0x160
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
kasan_slab_free include/linux/kasan.h:193 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook+0xbd/0x190 mm/slub.c:1749
slab_free mm/slub.c:3519 [inline]
kmem_cache_free+0x116/0x2e0 mm/slub.c:3535
kfree_skbmem+0x104/0x170
__kfree_skb net/core/skbuff.c:758 [inline]
consume_skb+0xb4/0x250 net/core/skbuff.c:930
__sk_msg_free+0x2dd/0x370 net/core/skmsg.c:205
sk_msg_free net/core/skmsg.c:218 [inline]
__sk_psock_purge_ingress_msg net/core/skmsg.c:769 [inline]
__sk_psock_zap_ingress net/core/skmsg.c:787 [inline]
sk_psock_stop+0x44c/0x4d0 net/core/skmsg.c:805
sk_psock_drop+0x219/0x310 net/core/skmsg.c:844
sk_psock_put include/linux/skmsg.h:458 [inline]
sock_map_unref+0x48f/0x4d0 net/core/sock_map.c:183
__sock_map_delete net/core/sock_map.c:425 [inline]
sock_map_delete_from_link net/core/sock_map.c:438 [inline]
sock_map_unlink net/core/sock_map.c:1496 [inline]
sock_map_remove_links+0x41c/0x650 net/core/sock_map.c:1511
sock_map_close+0x114/0x530 net/core/sock_map.c:1548
unix_release+0x82/0xc0 net/unix/af_unix.c:936
__sock_release net/socket.c:649 [inline]
sock_close+0xdf/0x270 net/socket.c:1336
__fput+0x228/0x8c0 fs/file_table.c:280
____fput+0x15/0x20 fs/file_table.c:308
task_work_run+0x129/0x190 kernel/task_work.c:188
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop+0xc4/0xe0 kernel/entry/common.c:181
exit_to_user_mode_prepare+0x5a/0xa0 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x26/0x160 kernel/entry/common.c:307
do_syscall_64+0x47/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f6fa3170719
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff3a406de8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f6fa3329a80 RCX: 00007f6fa3170719
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f6fa3329a80 R08: 0000000000000000 R09: 00007fff3a4070df
R10: 000000000003fd90 R11: 0000000000000246 R12: 0000000000221780
R13: 00007fff3a406ef0 R14: 0000000000000032 R15: ffffffffffffffff
Allocated by task 2959:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:45 [inline]
set_alloc_info mm/kasan/common.c:433 [inline]
__kasan_slab_alloc+0xb1/0xe0 mm/kasan/common.c:466
kasan_slab_alloc include/linux/kasan.h:217 [inline]
slab_post_alloc_hook+0x53/0x2c0 mm/slab.h:550
slab_alloc_node mm/slub.c:3240 [inline]
slab_alloc mm/slub.c:3248 [inline]
kmem_cache_alloc+0xf5/0x200 mm/slub.c:3253
skb_clone+0x1d1/0x360 net/core/skbuff.c:1547
sk_psock_verdict_recv+0x53/0x840 net/core/skmsg.c:1183
unix_read_sock+0x132/0x370 net/unix/af_unix.c:2428
sk_psock_verdict_data_ready+0x147/0x1a0 net/core/skmsg.c:1226
unix_dgram_sendmsg+0x15fa/0x2090 net/unix/af_unix.c:1942
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
____sys_sendmsg+0x59e/0x8f0 net/socket.c:2431
___sys_sendmsg+0x252/0x2e0 net/socket.c:2485
__sys_sendmsg net/socket.c:2514 [inline]
__do_sys_sendmsg net/socket.c:2523 [inline]
__se_sys_sendmsg+0x19a/0x260 net/socket.c:2521
__x64_sys_sendmsg+0x7b/0x90 net/socket.c:2521
x64_sys_call+0x16a/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Freed by task 20:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:45
kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
____kasan_slab_free+0x126/0x160 mm/kasan/common.c:365
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
kasan_slab_free include/linux/kasan.h:193 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook+0xbd/0x190 mm/slub.c:1749
slab_free mm/slub.c:3519 [inline]
kmem_cache_free+0x116/0x2e0 mm/slub.c:3535
kfree_skbmem+0x104/0x170
__kfree_skb net/core/skbuff.c:758 [inline]
kfree_skb_reason net/core/skbuff.c:778 [inline]
kfree_skb+0xc2/0x360 net/core/skbuff.c:792
sock_drop include/linux/skmsg.h:312 [inline]
sk_psock_backlog+0xc21/0xd90 net/core/skmsg.c:682
process_one_work+0x6bb/0xc10 kernel/workqueue.c:2325
worker_thread+0xad5/0x12a0 kernel/workqueue.c:2472
kthread+0x421/0x510 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
The buggy address belongs to the object at ffff88810d94b3c0
which belongs to the cache skbuff_head_cache of size 248
The buggy address is located 0 bytes inside of
248-byte region [ffff88810d94b3c0, ffff88810d94b4b8)
The buggy address belongs to the page:
page:ffffea00043652c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88810d94b140 pfn:0x10d94b
flags: 0x4000000000000200(slab|zone=1)
raw: 4000000000000200 0000000000000000 0000000b00000001 ffff8881081b2d80
raw: ffff88810d94b140 00000000800c0005 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY), pid 0, ts 18866660400, free_ts 18193916984
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x1a3/0x1b0 mm/page_alloc.c:2605
prep_new_page+0x1b/0x110 mm/page_alloc.c:2611
get_page_from_freelist+0x3550/0x35d0 mm/page_alloc.c:4485
__alloc_pages+0x27e/0x8f0 mm/page_alloc.c:5779
allocate_slab mm/slub.c:1932 [inline]
new_slab+0x9a/0x4e0 mm/slub.c:1995
___slab_alloc+0x39e/0x830 mm/slub.c:3028
__slab_alloc+0x4a/0x90 mm/slub.c:3115
slab_alloc_node mm/slub.c:3206 [inline]
slab_alloc mm/slub.c:3248 [inline]
kmem_cache_alloc+0x134/0x200 mm/slub.c:3253
__build_skb+0x2a/0x300 net/core/skbuff.c:242
build_skb+0x25/0x1f0 net/core/skbuff.c:259
page_to_skb+0x154/0xb40 drivers/net/virtio_net.c:440
receive_mergeable drivers/net/virtio_net.c:1070 [inline]
receive_buf+0xed6/0x57d0 drivers/net/virtio_net.c:1180
virtnet_receive drivers/net/virtio_net.c:1472 [inline]
virtnet_poll+0x615/0x1250 drivers/net/virtio_net.c:1585
__napi_poll+0xc4/0x5a0 net/core/dev.c:7042
napi_poll net/core/dev.c:7109 [inline]
net_rx_action+0x47d/0xc50 net/core/dev.c:7199
handle_softirqs+0x25e/0x5c0 kernel/softirq.c:565
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1472 [inline]
free_pcp_prepare mm/page_alloc.c:1544 [inline]
free_unref_page_prepare+0x7c8/0x7d0 mm/page_alloc.c:3534
free_unref_page_list+0x14b/0xa60 mm/page_alloc.c:3671
release_pages+0x1310/0x1370 mm/swap.c:1009
free_pages_and_swap_cache+0x8a/0xa0 mm/swap_state.c:320
tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:240 [inline]
tlb_flush_mmu mm/mmu_gather.c:247 [inline]
tlb_finish_mmu+0x177/0x320 mm/mmu_gather.c:338
exit_mmap+0x40d/0x940 mm/mmap.c:3218
__mmput+0x95/0x310 kernel/fork.c:1179
mmput+0x5b/0x170 kernel/fork.c:1202
exit_mm kernel/exit.c:554 [inline]
do_exit+0xb9c/0x2ca0 kernel/exit.c:867
do_group_exit+0x141/0x310 kernel/exit.c:1002
__do_sys_exit_group kernel/exit.c:1013 [inline]
__se_sys_exit_group kernel/exit.c:1011 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1011
x64_sys_call+0x610/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Memory state around the buggy address:
ffff88810d94b280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810d94b300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc
>ffff88810d94b380: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
^
ffff88810d94b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810d94b480: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc
==================================================================