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SubjectKASAN: user-memory-access Read in do_con_write (2)

syzbot found the following crash on:

HEAD commit: 4e99b321 Merge tag 'nfs-for-5.8-2' of git://git.linux-nfs...
git tree: upstream
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:

BUG: KASAN: user-memory-access in memcpy include/linux/string.h:406 [inline]
BUG: KASAN: user-memory-access in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: user-memory-access in delete_char drivers/tty/vt/vt.c:858 [inline]
BUG: KASAN: user-memory-access in csi_P drivers/tty/vt/vt.c:2013 [inline]
BUG: KASAN: user-memory-access in do_con_trol drivers/tty/vt/vt.c:2407 [inline]
BUG: KASAN: user-memory-access in do_con_write+0x6f90/0x7400 drivers/tty/vt/vt.c:2823
Read of size 118 at addr 00000000ffffff9a by task syz-executor.4/10580

CPU: 0 PID: 10580 Comm: syz-executor.4 Not tainted 5.8.0-rc2-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
__kasan_report mm/kasan/report.c:517 [inline]
kasan_report.cold+0x5/0x37 mm/kasan/report.c:530
check_memory_region_inline mm/kasan/generic.c:186 [inline]
check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
memcpy+0x20/0x60 mm/kasan/common.c:105
memcpy include/linux/string.h:406 [inline]
scr_memcpyw include/linux/vt_buffer.h:49 [inline]
delete_char drivers/tty/vt/vt.c:858 [inline]
csi_P drivers/tty/vt/vt.c:2013 [inline]
do_con_trol drivers/tty/vt/vt.c:2407 [inline]
do_con_write+0x6f90/0x7400 drivers/tty/vt/vt.c:2823
con_write+0x22/0xb0 drivers/tty/vt/vt.c:3159
process_output_block drivers/tty/n_tty.c:595 [inline]
n_tty_write+0x3ce/0xf80 drivers/tty/n_tty.c:2333
do_tty_write drivers/tty/tty_io.c:962 [inline]
tty_write+0x4d9/0x870 drivers/tty/tty_io.c:1046
__vfs_write+0x76/0x100 fs/read_write.c:495
vfs_write+0x268/0x5d0 fs/read_write.c:559
ksys_write+0x12d/0x250 fs/read_write.c:612
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
RIP: 0033:0x45cb19
Code: Bad RIP value.
RSP: 002b:00007fcc7ee74c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000050e080 RCX: 000000000045cb19
RDX: 0000000000000320 RSI: 00000000200001c0 RDI: 0000000000000007
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000d2a R14: 00000000004cf845 R15: 00007fcc7ee756d4

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