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Linux kernel source tree
864f9963ec
Our in-house Syzkaller reported the following BUG (twice), which we
believed was the same issue with [1]:
==================================================================
BUG: KASAN: slab-out-of-bounds in vcs_scr_readw+0xc2/0xd0 drivers/tty/vt/vt.c:4740
Read of size 2 at addr ffff88800f5bef60 by task syz.7.2620/12393
...
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x72/0xa0 lib/dump_stack.c:106
print_address_description.constprop.0+0x6b/0x3d0 mm/kasan/report.c:364
print_report+0xba/0x280 mm/kasan/report.c:475
kasan_report+0xa9/0xe0 mm/kasan/report.c:588
vcs_scr_readw+0xc2/0xd0 drivers/tty/vt/vt.c:4740
vcs_write_buf_noattr drivers/tty/vt/vc_screen.c:493 [inline]
vcs_write+0x586/0x840 drivers/tty/vt/vc_screen.c:690
vfs_write+0x219/0x960 fs/read_write.c:584
ksys_write+0x12e/0x260 fs/read_write.c:639
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x59/0x110 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x78/0xe2
...
</TASK>
Allocated by task 5614:
kasan_save_stack+0x20/0x40 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383
kasan_kmalloc include/linux/kasan.h:201 [inline]
__do_kmalloc_node mm/slab_common.c:1007 [inline]
__kmalloc+0x62/0x140 mm/slab_common.c:1020
kmalloc include/linux/slab.h:604 [inline]
kzalloc include/linux/slab.h:721 [inline]
vc_do_resize+0x235/0xf40 drivers/tty/vt/vt.c:1193
vgacon_adjust_height+0x2d4/0x350 drivers/video/console/vgacon.c:1007
vgacon_font_set+0x1f7/0x240 drivers/video/console/vgacon.c:1031
con_font_set drivers/tty/vt/vt.c:4628 [inline]
con_font_op+0x4da/0xa20 drivers/tty/vt/vt.c:4675
vt_k_ioctl+0xa10/0xb30 drivers/tty/vt/vt_ioctl.c:474
vt_ioctl+0x14c/0x1870 drivers/tty/vt/vt_ioctl.c:752
tty_ioctl+0x655/0x1510 drivers/tty/tty_io.c:2779
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0x12d/0x190 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x59/0x110 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x78/0xe2
Last potentially related work creation:
kasan_save_stack+0x20/0x40 mm/kasan/common.c:45
__kasan_record_aux_stack+0x94/0xa0 mm/kasan/generic.c:492
__call_rcu_common.constprop.0+0xc3/0xa10 kernel/rcu/tree.c:2713
netlink_release+0x620/0xc20 net/netlink/af_netlink.c:802
__sock_release+0xb5/0x270 net/socket.c:663
sock_close+0x1e/0x30 net/socket.c:1425
__fput+0x408/0xab0 fs/file_table.c:384
__fput_sync+0x4c/0x60 fs/file_table.c:465
__do_sys_close fs/open.c:1580 [inline]
__se_sys_close+0x68/0xd0 fs/open.c:1565
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x59/0x110 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x78/0xe2
Second to last potentially related work creation:
kasan_save_stack+0x20/0x40 mm/kasan/common.c:45
__kasan_record_aux_stack+0x94/0xa0 mm/kasan/generic.c:492
__call_rcu_common.constprop.0+0xc3/0xa10 kernel/rcu/tree.c:2713
netlink_release+0x620/0xc20 net/netlink/af_netlink.c:802
__sock_release+0xb5/0x270 net/socket.c:663
sock_close+0x1e/0x30 net/socket.c:1425
__fput+0x408/0xab0 fs/file_table.c:384
task_work_run+0x154/0x240 kernel/task_work.c:239
exit_task_work include/linux/task_work.h:45 [inline]
do_exit+0x8e5/0x1320 kernel/exit.c:874
do_group_exit+0xcd/0x280 kernel/exit.c:1023
get_signal+0x1675/0x1850 kernel/signal.c:2905
arch_do_signal_or_restart+0x80/0x3b0 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x1b3/0x1e0 kernel/entry/common.c:218
do_syscall_64+0x66/0x110 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x78/0xe2
The buggy address belongs to the object at ffff88800f5be000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 2656 bytes to the right of
allocated 1280-byte region [ffff88800f5be000, ffff88800f5be500)
...
Memory state around the buggy address:
ffff88800f5bee00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88800f5bee80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88800f5bef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88800f5bef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88800f5bf000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================
By analyzing the vmcore, we found that vc->vc_origin was somehow placed
one line prior to vc->vc_screenbuf when vc was in KD_TEXT mode, and
further writings to /dev/vcs caused out-of-bounds reads (and writes
right after) in vcs_write_buf_noattr().
Our further experiments show that in most cases, vc->vc_origin equals to
vga_vram_base when the console is in KD_TEXT mode, and it's around
vc->vc_screenbuf for the KD_GRAPHICS mode. But via triggerring a
TIOCL_SETVESABLANK ioctl beforehand, we can make vc->vc_origin be around
vc->vc_screenbuf while the console is in KD_TEXT mode, and then by
writing the special 'ESC M' control sequence to the tty certain times
(depends on the value of `vc->state.y - vc->vc_top`), we can eventually
move vc->vc_origin prior to vc->vc_screenbuf. Here's the PoC, tested on
QEMU:
```
int main() {
const int RI_NUM = 10; // should be greater than `vc->state.y - vc->vc_top`
int tty_fd, vcs_fd;
const char *tty_path = "/dev/tty0";
const char *vcs_path = "/dev/vcs";
const char escape_seq[] = "\x1bM"; // ESC + M
const char trigger_seq[] = "Let's trigger an OOB write.";
struct vt_sizes vt_size = { 70, 2 };
int blank = TIOCL_BLANKSCREEN;
tty_fd = open(tty_path, O_RDWR);
char vesa_mode[] = { TIOCL_SETVESABLANK, 1 };
ioctl(tty_fd, TIOCLINUX, vesa_mode);
ioctl(tty_fd, TIOCLINUX, &blank);
ioctl(tty_fd, VT_RESIZE, &vt_size);
for (int i = 0; i < RI_NUM; ++i)
write(tty_fd, escape_seq, sizeof(escape_seq) - 1);
vcs_fd = open(vcs_path, O_RDWR);
write(vcs_fd, trigger_seq, sizeof(trigger_seq));
close(vcs_fd);
close(tty_fd);
return 0;
}
```
To solve this problem, add an address range validation check in
vgacon_scroll(), ensuring vc->vc_origin never precedes vc_screenbuf.
Reported-by: syzbot+9c09fda97a1a65ea859b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9c09fda97a1a65ea859b [1]
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.