KASAN: null-ptr-deref Read in do_con_trol

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 35766839 Linux 4.19.103
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10d457a5e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=84f14e7b6cbc7d27
dashboard link: https://syzkaller.appspot.com/bug?extid=2057b655d6a3fa9bb8a5
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1123a431e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1130f7a5e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2057b6...@syzkaller.appspotmail.com

audit: type=1400 audit(1581668315.933:36): avc: denied { map } for pid=8048 comm="syz-executor847" path="/root/syz-executor847156921" dev="sda1" ino=16483 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: null-ptr-deref in memcpy include/linux/string.h:348 [inline]
BUG: KASAN: null-ptr-deref in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: null-ptr-deref in delete_char drivers/tty/vt/vt.c:852 [inline]
BUG: KASAN: null-ptr-deref in csi_P drivers/tty/vt/vt.c:1986 [inline]
BUG: KASAN: null-ptr-deref in do_con_trol+0x3b9/0x6070 drivers/tty/vt/vt.c:2360
Read of size 4294967294 at addr 0000000000000012 by task syz-executor847/8048

CPU: 0 PID: 8048 Comm: syz-executor847 Not tainted 4.19.103-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+0x197/0x210 lib/dump_stack.c:118
kasan_report_error mm/kasan/report.c:352 [inline]
kasan_report mm/kasan/report.c:412 [inline]
kasan_report.cold+0x199/0x2ba mm/kasan/report.c:396
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x123/0x190 mm/kasan/kasan.c:267
memcpy+0x24/0x50 mm/kasan/kasan.c:302
memcpy include/linux/string.h:348 [inline]
scr_memcpyw include/linux/vt_buffer.h:49 [inline]
delete_char drivers/tty/vt/vt.c:852 [inline]
csi_P drivers/tty/vt/vt.c:1986 [inline]
do_con_trol+0x3b9/0x6070 drivers/tty/vt/vt.c:2360
do_con_write.part.0+0xfd5/0x1eb0 drivers/tty/vt/vt.c:2773
do_con_write drivers/tty/vt/vt.c:2541 [inline]
con_write+0x46/0xd0 drivers/tty/vt/vt.c:3110
process_output_block drivers/tty/n_tty.c:593 [inline]
n_tty_write+0x3f9/0x1140 drivers/tty/n_tty.c:2331
do_tty_write drivers/tty/tty_io.c:960 [inline]
tty_write+0x458/0x7a0 drivers/tty/tty_io.c:1044
__vfs_write+0x114/0x810 fs/read_write.c:485
vfs_write+0x20c/0x560 fs/read_write.c:549
ksys_write+0x14f/0x2d0 fs/read_write.c:599
__do_sys_write fs/read_write.c:611 [inline]
__se_sys_write fs/read_write.c:608 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:608
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4404f9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffefc0bbca8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004404f9
RDX: 0000000000000078 RSI: 0000000020000140 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401de0
R13: 0000000000401e70 R14: 0000000000000000 R15: 0000000000000000
==================================================================


---
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[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 98db2bf2 Linux 4.14.171
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16b5434ee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=9dc3f6f9d0ff3b98
dashboard link: https://syzkaller.appspot.com/bug?extid=19b3be1e1d860fcc6f31

compiler: gcc (GCC) 9.0.0 20181231 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=165d96b5e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1499c07ee00000

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

Reported-by: syzbot+19b3be...@syzkaller.appspotmail.com

audit: type=1400 audit(1581724839.850:36): avc: denied { map } for pid=7271 comm="syz-executor966" path="/root/syz-executor966765308" dev="sda1" ino=16484 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
BUG: KASAN: null-ptr-deref in memcpy include/linux/string.h:347 [inline]

BUG: KASAN: null-ptr-deref in scr_memcpyw include/linux/vt_buffer.h:49 [inline]

BUG: KASAN: null-ptr-deref in delete_char drivers/tty/vt/vt.c:546 [inline]
BUG: KASAN: null-ptr-deref in csi_P drivers/tty/vt/vt.c:1648 [inline]
BUG: KASAN: null-ptr-deref in do_con_trol+0x3188/0x5b40 drivers/tty/vt/vt.c:2022
Read of size 4294967294 at addr 0000000000000012 by task syz-executor966/7271

CPU: 1 PID: 7271 Comm: syz-executor966 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+0x142/0x197 lib/dump_stack.c:58
kasan_report_error mm/kasan/report.c:349 [inline]
kasan_report mm/kasan/report.c:409 [inline]
kasan_report.cold+0x127/0x2af mm/kasan/report.c:393

check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x123/0x190 mm/kasan/kasan.c:267
memcpy+0x24/0x50 mm/kasan/kasan.c:302

memcpy include/linux/string.h:347 [inline]
scr_memcpyw include/linux/vt_buffer.h:49 [inline]
delete_char drivers/tty/vt/vt.c:546 [inline]
csi_P drivers/tty/vt/vt.c:1648 [inline]
do_con_trol+0x3188/0x5b40 drivers/tty/vt/vt.c:2022
do_con_write.part.0+0xcc7/0x1b50 drivers/tty/vt/vt.c:2434
do_con_write drivers/tty/vt/vt.c:2205 [inline]
con_write+0x38/0xc0 drivers/tty/vt/vt.c:2787
process_output_block drivers/tty/n_tty.c:595 [inline]
n_tty_write+0x38b/0xf20 drivers/tty/n_tty.c:2333
do_tty_write drivers/tty/tty_io.c:959 [inline]
tty_write+0x3f6/0x700 drivers/tty/tty_io.c:1043
__vfs_write+0x105/0x6b0 fs/read_write.c:480
vfs_write+0x198/0x500 fs/read_write.c:544
SYSC_write fs/read_write.c:590 [inline]
SyS_write+0xfd/0x230 fs/read_write.c:582
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4404f9
RSP: 002b:00007ffd13d27c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000001

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 74752b81eae8ae64e97de222320026367e92c4b5
Author: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
Date: Sun Jul 12 11:10:12 2020 +0000

vt: Reject zero-sized screen buffer size.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11048e6a900000
start commit: 35766839 Linux 4.19.103
git tree: linux-4.19.y

kernel config: https://syzkaller.appspot.com/x/.config?x=84f14e7b6cbc7d27
dashboard link: https://syzkaller.appspot.com/bug?extid=2057b655d6a3fa9bb8a5

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1123a431e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1130f7a5e00000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: vt: Reject zero-sized screen buffer size.

For information about bisection process see: https://goo.gl/tpsmEJ#bisection