Message-ID: <2025032703-CVE-2023-52973-a993@gregkh>
Date: Thu, 27 Mar 2025 17:43:20 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2023-52973: vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF

After a call to console_unlock() in vcs_read() the vc_data struct can be
freed by vc_deallocate(). Because of that, the struct vc_data pointer
load must be done at the top of while loop in vcs_read() to avoid a UAF
when vcs_size() is called.

Syzkaller reported a UAF in vcs_size().

BUG: KASAN: use-after-free in vcs_size (drivers/tty/vt/vc_screen.c:215)
Read of size 4 at addr ffff8881137479a8 by task 4a005ed81e27e65/1537

CPU: 0 PID: 1537 Comm: 4a005ed81e27e65 Not tainted 6.2.0-rc5 #1
Hardware name: Red Hat KVM, BIOS 1.15.0-2.module
Call Trace:
  <TASK>
__asan_report_load4_noabort (mm/kasan/report_generic.c:350)
vcs_size (drivers/tty/vt/vc_screen.c:215)
vcs_read (drivers/tty/vt/vc_screen.c:415)
vfs_read (fs/read_write.c:468 fs/read_write.c:450)
...
  </TASK>

Allocated by task 1191:
...
kmalloc_trace (mm/slab_common.c:1069)
vc_allocate (./include/linux/slab.h:580 ./include/linux/slab.h:720
     drivers/tty/vt/vt.c:1128 drivers/tty/vt/vt.c:1108)
con_install (drivers/tty/vt/vt.c:3383)
tty_init_dev (drivers/tty/tty_io.c:1301 drivers/tty/tty_io.c:1413
     drivers/tty/tty_io.c:1390)
tty_open (drivers/tty/tty_io.c:2080 drivers/tty/tty_io.c:2126)
chrdev_open (fs/char_dev.c:415)
do_dentry_open (fs/open.c:883)
vfs_open (fs/open.c:1014)
...

Freed by task 1548:
...
kfree (mm/slab_common.c:1021)
vc_port_destruct (drivers/tty/vt/vt.c:1094)
tty_port_destructor (drivers/tty/tty_port.c:296)
tty_port_put (drivers/tty/tty_port.c:312)
vt_disallocate_all (drivers/tty/vt/vt_ioctl.c:662 (discriminator 2))
vt_ioctl (drivers/tty/vt/vt_ioctl.c:903)
tty_ioctl (drivers/tty/tty_io.c:2776)
...

The buggy address belongs to the object at ffff888113747800
  which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 424 bytes inside of
  1024-byte region [ffff888113747800, ffff888113747c00)

The buggy address belongs to the physical page:
page:00000000b3fe6c7c refcount:1 mapcount:0 mapping:0000000000000000
     index:0x0 pfn:0x113740
head:00000000b3fe6c7c order:3 compound_mapcount:0 subpages_mapcount:0
     compound_pincount:0
anon flags: 0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
raw: 0017ffffc0010200 ffff888100042dc0 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff888113747880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff888113747900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff888113747980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                   ^
  ffff888113747a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff888113747a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Disabling lock debugging due to kernel taint

The Linux kernel CVE team has assigned CVE-2023-52973 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 4.14.329 with commit af79ea9a2443016f64d8fd8d72020cc874f0e066
	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 4.19.273 with commit 6332f52f44b9776568bf3c0b714ddfb0bb175e78
	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 5.4.232 with commit d0332cbf53dad06a22189cc341391237f4ea6d9f
	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 5.10.168 with commit 55515d7d8743b71b80bfe68e89eb9d92630626ab
	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 5.15.93 with commit fc9e27f3ba083534b8bbf72ab0f5c810ffdc7d18
	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 6.1.11 with commit 8506f16aae9daf354e3732bcfd447e2a97f023df
	Issue introduced in 2.6.38 with commit ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff and fixed in 6.2 with commit 226fae124b2dac217ea5436060d623ff3385bc34

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-2023-52973
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/tty/vt/vc_screen.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/af79ea9a2443016f64d8fd8d72020cc874f0e066
	https://git.kernel.org/stable/c/6332f52f44b9776568bf3c0b714ddfb0bb175e78
	https://git.kernel.org/stable/c/d0332cbf53dad06a22189cc341391237f4ea6d9f
	https://git.kernel.org/stable/c/55515d7d8743b71b80bfe68e89eb9d92630626ab
	https://git.kernel.org/stable/c/fc9e27f3ba083534b8bbf72ab0f5c810ffdc7d18
	https://git.kernel.org/stable/c/8506f16aae9daf354e3732bcfd447e2a97f023df
	https://git.kernel.org/stable/c/226fae124b2dac217ea5436060d623ff3385bc34

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