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BUG: KASAN: use-after-free in vcs_read_buf drivers/tty/vt/vc_screen.c:357 [inline]
BUG: KASAN: use-after-free in vcs_read+0xaa7/0xb40 drivers/tty/vt/vc_screen.c:449
Write of size 2 at addr ffff8880931f3000 by task syz-executor.3/16918

CPU: 0 PID: 16918 Comm: syz-executor.3 Not tainted 5.9.0-rc1-next-20200821-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/0x497 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 vcs_read_buf drivers/tty/vt/vc_screen.c:357 [inline]
 vcs_read+0xaa7/0xb40 drivers/tty/vt/vc_screen.c:449
 do_loop_readv_writev fs/read_write.c:734 [inline]
 do_loop_readv_writev fs/read_write.c:721 [inline]
 do_iter_read+0x48e/0x6e0 fs/read_write.c:955
 vfs_readv+0xe5/0x150 fs/read_write.c:1073
 do_preadv fs/read_write.c:1165 [inline]
 __do_sys_preadv fs/read_write.c:1215 [inline]
 __se_sys_preadv fs/read_write.c:1210 [inline]
 __x64_sys_preadv+0x231/0x310 fs/read_write.c:1210
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d4d9
Code: 5d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffb633bcc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 0000000000025780 RCX: 000000000045d4d9
RDX: 0000000000000001 RSI: 0000000020001680 RDI: 0000000000000003
RBP: 000000000118cf90 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffd4bf315df R14: 00007ffb633bd9c0 R15: 000000000118cf4c

Allocated by task 6875:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
 kmalloc_node include/linux/slab.h:577 [inline]
 kvmalloc_node+0x61/0xf0 mm/util.c:575
 kvmalloc include/linux/mm.h:753 [inline]
 xt_alloc_table_info+0x3c/0xa0 net/netfilter/x_tables.c:1176
 do_replace net/ipv6/netfilter/ip6_tables.c:1141 [inline]
 do_ip6t_set_ctl+0x500/0xb73 net/ipv6/netfilter/ip6_tables.c:1636
 nf_setsockopt+0x83/0xe0 net/netfilter/nf_sockopt.c:101
 ipv6_setsockopt+0x122/0x180 net/ipv6/ipv6_sockglue.c:1008
 tcp_setsockopt+0x136/0x24a0 net/ipv4/tcp.c:3333
 __sys_setsockopt+0x2db/0x610 net/socket.c:2132
 __do_sys_setsockopt net/socket.c:2143 [inline]
 __se_sys_setsockopt net/socket.c:2140 [inline]
 __x64_sys_setsockopt+0xba/0x150 net/socket.c:2140
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff8880931f3000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 0 bytes inside of
 2048-byte region [ffff8880931f3000, ffff8880931f3800)
The buggy address belongs to the page:
page:00000000197cea44 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x931f3
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00023787c8 ffffea0002378148 ffff8880aa040800
raw: 0000000000000000 ffff8880931f3000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880931f2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880931f2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880931f3000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8880931f3080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880931f3100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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