Amazon Linux AMI: CVE-2023-52973: Security patch for kernel (ALAS-2025-1975)

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