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BUG: KASAN: use-after-free in n_tty_check_throttle drivers/tty/n_tty.c:266 [inline]
BUG: KASAN: use-after-free in n_tty_receive_buf_common+0x2075/0x2480 drivers/tty/n_tty.c:1761
Read of size 1 at addr ffff88808f4d4a00 by task syz-executor756/15391

CPU: 1 PID: 15391 Comm: syz-executor756 Not tainted 4.14.171-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x13e/0x194 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1e2 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2ae mm/kasan/report.c:393
 n_tty_check_throttle drivers/tty/n_tty.c:266 [inline]
 n_tty_receive_buf_common+0x2075/0x2480 drivers/tty/n_tty.c:1761
 tty_ldisc_receive_buf+0x9e/0x170 drivers/tty/tty_buffer.c:455
 paste_selection+0x1da/0x3ca drivers/tty/vt/selection.c:360
 tioclinux+0x107/0x410 drivers/tty/vt/vt.c:2696
 vt_ioctl+0x169a/0x2010 drivers/tty/vt/vt_ioctl.c:364
 tty_ioctl+0x6c5/0x1220 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441339
RSP: 002b:00007ffee31737b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441339
RDX: 0000000020000000 RSI: 000000000000541c RDI: 0000000000000004
RBP: 00000000000e31b6 R08: 000000000000000d R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004020b0
R13: 0000000000402140 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 15391:
 save_stack+0x32/0xa0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xbf/0xe0 mm/kasan/kasan.c:529
 __do_kmalloc mm/slab.c:3720 [inline]
 __kmalloc+0x15b/0x7c0 mm/slab.c:3729
 kmalloc include/linux/slab.h:493 [inline]
 set_selection+0x78c/0xde0 drivers/tty/vt/selection.c:295
 tioclinux+0xf0/0x410 drivers/tty/vt/vt.c:2692
 vt_ioctl+0x169a/0x2010 drivers/tty/vt/vt_ioctl.c:364
 tty_ioctl+0x6c5/0x1220 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 15393:
 save_stack+0x32/0xa0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcb/0x260 mm/slab.c:3815
 set_selection+0x7a9/0xde0 drivers/tty/vt/selection.c:301
 tioclinux+0xf0/0x410 drivers/tty/vt/vt.c:2692
 vt_ioctl+0x169a/0x2010 drivers/tty/vt/vt_ioctl.c:364
 tty_ioctl+0x6c5/0x1220 drivers/tty/tty_io.c:2661
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88808f4d4a00
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes inside of
 32-byte region [ffff88808f4d4a00, ffff88808f4d4a20)
The buggy address belongs to the page:
page:ffffea00023d3500 count:1 mapcount:0 mapping:ffff88808f4d4000 index:0xffff88808f4d4fc1
flags: 0xfffe0000000100(slab)
raw: 00fffe0000000100 ffff88808f4d4000 ffff88808f4d4fc1 000000010000003f
raw: ffffea00027e2660 ffffea00027e74e0 ffff88812fe561c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808f4d4900: fb fb fb fb fc fc fc fc 00 00 02 fc fc fc fc fc
 ffff88808f4d4980: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff88808f4d4a00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                   ^
 ffff88808f4d4a80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff88808f4d4b00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
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