(We analyzed the crash and added the result below.)
We report the crash:
"KASAN: use-after-free Read in vgacon_invert_region"
This crash was found in v4.17-rc3. Specifically, memory access (read
operation) is invalid and which is detected by KASAN.
Analysis:
The function "vt_do_resize" basically allows for resizing the screen
buffer (i.e., vc_data) beyond memory address 0x10
(i.e., 0x8810 in this case).
We think, however, a certain memory area starting from 0x10 is protected.
So subsequent memory access beyond this address (by
"vgacon_invert_region") causes memory access violation.
C repro code:
https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/repro-ba6c1.c
kernel config:
https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/kernel-config-v4.17-rc3
Crash log:
==
BUG: KASAN: use-after-free in vgacon_invert_region+0xf9/0x100
drivers/video/console/vgacon.c:663
Read of size 2 at addr 8810 by task syz-executor3/525
CPU: 0 PID: 525 Comm: syz-executor3 Not tainted 4.17.0-rc3 #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xc7/0x138 lib/dump_stack.c:113
print_address_description+0x78/0x290 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x234/0x350 mm/kasan/report.c:412
__asan_report_load2_noabort+0x19/0x20 mm/kasan/report.c:431
vgacon_invert_region+0xf9/0x100 drivers/video/console/vgacon.c:663
invert_screen+0x197/0x630 drivers/tty/vt/vt.c:461
highlight drivers/tty/vt/selection.c:51 [inline]
set_selection+0x6b7/0xf60 drivers/tty/vt/selection.c:276
tioclinux+0x126/0x410 drivers/tty/vt/vt.c:2691
vt_ioctl+0x1036/0x2580 drivers/tty/vt/vt_ioctl.c:362
tty_ioctl+0x288/0x14c0 drivers/tty/tty_io.c:2646
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x191/0xfe0 fs/ioctl.c:686
ksys_ioctl+0x99/0xb0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x78/0xb0 fs/ioctl.c:706
do_syscall_64+0xb0/0x460 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4497b9
RSP: 002b:7f720c4bec68 EFLAGS: 0246 ORIG_RAX: 0010
RAX: ffda RBX: 7f720c4bf6cc RCX: 004497b9
RDX: 2040 RSI: 0002541c RDI: 0013
RBP: 0071bf58 R08: R09:
R10: R11: 0246 R12:
R13: 5aa8 R14: 006ecb48 R15: 7f720c4bf700
The buggy address belongs to the page:
page:ea004000 count:0 mapcount:-127 mapping: index:0x0
flags: 0x0()
raw: ff80
raw: 88013fff9300 88013fff9300 0008
page dumped because: kasan: bad access detected
Memory state around the buggy address:
880fff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
880fff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>8810: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
88100080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
88100100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==
Thanks,
Kyungtae Kim
On Thu, May 17, 2018 at 2:04 PM, Kyungtae Kim <kt0...@gmail.com> wrote:
> We report the crash:
> "KASAN: use-after-free Read in vgacon_invert_region"
>
> This crash was found in v4.17-rc3. Specifically, memory access (read
> operation) is invalid, and it is detected by KASAN.
>
> C repro code:
> https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/repro-ba6c1.c
> kernel config:
> https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/kernel-config-v4.17-rc3
>
> Crash log:
> ==
> BUG: KASAN: use-after-free in vgacon_invert_region+0xf9/0x100
> drivers/video/console/vgacon.c:663
> Read of size 2 at addr 8810 by task syz-executor3/525
>
> CPU: 0 PID: 525 Comm: syz-executor3 Not tainted 4.17.0-rc3 #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0xc7/0x138 lib/dump_stack.c:113
> print_address_description+0x78/0x290 mm/kasan/report.c:256
> kasan_report_error mm/kasan/report.c:354 [inline]
> kasan_report+0x234/0x350 mm/kasan/report.c:412
> __asan_report_load2_noabort+0x19/0x20 mm/kasan/report.c:431
> vgacon_invert_region+0xf9/0x100 drivers/video/console/vgacon.c:663
> invert_screen+0x197/0x630 drivers/tty/vt/vt.c:461
> highlight drivers/tty/vt/selection.c:51 [inline]
> set_selection+0x6b7/0xf60 drivers/tty/vt/selection.c:276
> tioclinux+0x
