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BUG: KASAN: use-after-free in soft_cursor+0x62c/0xdb0 drivers/video/fbdev/core/softcursor.c:61
Read of size 1 at addr ffff8880a2d2b944 by task kworker/0:51/3009

CPU: 0 PID: 3009 Comm: kworker/0:51 Not tainted 5.6.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_power_efficient fb_flashcursor
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 print_address_description+0x74/0x5c0 mm/kasan/report.c:374
 __kasan_report+0x14b/0x1c0 mm/kasan/report.c:506
 kasan_report+0x25/0x50 mm/kasan/common.c:641
 soft_cursor+0x62c/0xdb0 drivers/video/fbdev/core/softcursor.c:61
 bit_cursor+0x178a/0x2180 drivers/video/fbdev/core/bitblit.c:386
 fb_flashcursor+0x73e/0xa10 drivers/video/fbdev/core/fbcon.c:417
 process_one_work+0x76e/0xfd0 kernel/workqueue.c:2266
 worker_thread+0xa7f/0x1450 kernel/workqueue.c:2412
 kthread+0x317/0x340 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 11693:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc+0x118/0x1c0 mm/kasan/common.c:515
 __kmalloc_reserve net/core/skbuff.c:142 [inline]
 __alloc_skb+0xde/0x4f0 net/core/skbuff.c:210
 alloc_skb include/linux/skbuff.h:1081 [inline]
 netlink_alloc_large_skb net/netlink/af_netlink.c:1175 [inline]
 netlink_sendmsg+0x7b2/0xd70 net/netlink/af_netlink.c:1893
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x4f9/0x7c0 net/socket.c:2343
 ___sys_sendmsg net/socket.c:2397 [inline]
 __sys_sendmmsg+0x2a9/0x5b0 net/socket.c:2487
 __do_sys_sendmmsg net/socket.c:2516 [inline]
 __se_sys_sendmmsg net/socket.c:2513 [inline]
 __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2513
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 11693:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0x12e/0x1e0 mm/kasan/common.c:476
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x220 mm/slab.c:3757
 skb_release_all net/core/skbuff.c:664 [inline]
 __kfree_skb+0x56/0x1c0 net/core/skbuff.c:678
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x78e/0x940 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0xa57/0xd70 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x4f9/0x7c0 net/socket.c:2343
 ___sys_sendmsg net/socket.c:2397 [inline]
 __sys_sendmmsg+0x2a9/0x5b0 net/socket.c:2487
 __do_sys_sendmmsg net/socket.c:2516 [inline]
 __se_sys_sendmmsg net/socket.c:2513 [inline]
 __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2513
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a2d2b800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 324 bytes inside of
 512-byte region [ffff8880a2d2b800, ffff8880a2d2ba00)
The buggy address belongs to the page:
page:ffffea00028b4ac0 refcount:1 mapcount:0 mapping:ffff8880aa400a80 index:0xffff8880a2d2b000
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002463c08 ffffea00023b5e88 ffff8880aa400a80
raw: ffff8880a2d2b000 ffff8880a2d2b000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a2d2b800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a2d2b880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880a2d2b900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                           ^
 ffff8880a2d2b980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a2d2ba00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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