Subject: CVE-2024-50073: tty: n_gsm: Fix use-after-free in gsm_cleanup_mux

From: Greg Kroah-Hartman <[email-masked]>

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

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

tty: n_gsm: Fix use-after-free in gsm_cleanup_mux

BUG: KASAN: slab-use-after-free in gsm_cleanup_mux+0x77b/0x7b0
drivers/tty/n_gsm.c:3160 [n_gsm]
Read of size 8 at addr ffff88815fe99c00 by task poc/3379
CPU: 0 UID: 0 PID: 3379 Comm: poc Not tainted 6.11.0+ #56
Hardware name: VMware, Inc. VMware Virtual Platform/440BX
Desktop Reference Platform, BIOS 6.00 11/12/2020
Call Trace:
 <TASK>
 gsm_cleanup_mux+0x77b/0x7b0 drivers/tty/n_gsm.c:3160 [n_gsm]
 __pfx_gsm_cleanup_mux+0x10/0x10 drivers/tty/n_gsm.c:3124 [n_gsm]
 __pfx_sched_clock_cpu+0x10/0x10 kernel/sched/clock.c:389
 update_load_avg+0x1c1/0x27b0 kernel/sched/fair.c:4500
 __pfx_min_vruntime_cb_rotate+0x10/0x10 kernel/sched/fair.c:846
 __rb_insert_augmented+0x492/0xbf0 lib/rbtree.c:161
 gsmld_ioctl+0x395/0x1450 drivers/tty/n_gsm.c:3408 [n_gsm]
 _raw_spin_lock_irqsave+0x92/0xf0 arch/x86/include/asm/atomic.h:107
 __pfx_gsmld_ioctl+0x10/0x10 drivers/tty/n_gsm.c:3822 [n_gsm]
 ktime_get+0x5e/0x140 kernel/time/timekeeping.c:195
 ldsem_down_read+0x94/0x4e0 arch/x86/include/asm/atomic64_64.h:79
 __pfx_ldsem_down_read+0x10/0x10 drivers/tty/tty_ldsem.c:338
 __pfx_do_vfs_ioctl+0x10/0x10 fs/ioctl.c:805
 tty_ioctl+0x643/0x1100 drivers/tty/tty_io.c:2818

Allocated by task 65:
 gsm_data_alloc.constprop.0+0x27/0x190 drivers/tty/n_gsm.c:926 [n_gsm]
 gsm_send+0x2c/0x580 drivers/tty/n_gsm.c:819 [n_gsm]
 gsm1_receive+0x547/0xad0 drivers/tty/n_gsm.c:3038 [n_gsm]
 gsmld_receive_buf+0x176/0x280 drivers/tty/n_gsm.c:3609 [n_gsm]
 tty_ldisc_receive_buf+0x101/0x1e0 drivers/tty/tty_buffer.c:391
 tty_port_default_receive_buf+0x61/0xa0 drivers/tty/tty_port.c:39
 flush_to_ldisc+0x1b0/0x750 drivers/tty/tty_buffer.c:445
 process_scheduled_works+0x2b0/0x10d0 kernel/workqueue.c:3229
 worker_thread+0x3dc/0x950 kernel/workqueue.c:3391
 kthread+0x2a3/0x370 kernel/kthread.c:389
 ret_from_fork+0x2d/0x70 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:257

Freed by task 3367:
 kfree+0x126/0x420 mm/slub.c:4580
 gsm_cleanup_mux+0x36c/0x7b0 drivers/tty/n_gsm.c:3160 [n_gsm]
 gsmld_ioctl+0x395/0x1450 drivers/tty/n_gsm.c:3408 [n_gsm]
 tty_ioctl+0x643/0x1100 drivers/tty/tty_io.c:2818

[Analysis]
gsm_msg on the tx_ctrl_list or tx_data_list of gsm_mux
can be freed by multi threads through ioctl,which leads
to the occurrence of uaf. Protect it by gsm tx lock.

The Linux kernel CVE team has assigned CVE-2024-50073 to this issue.

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

	Fixed in 6.1.114 with commit bf171b5e86e4
	Fixed in 6.6.58 with commit c29f192e0d44
	Fixed in 6.11.5 with commit 0eec592c6a74
	Fixed in 6.12-rc4 with commit 9462f4ca56e7

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-2024-50073
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/n_gsm.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/bf171b5e86e41de4c1cf32fb7aefa275c3d7de49
	https://git.kernel.org/stable/c/c29f192e0d44cc1cbaf698fa1ff198f63556691a
	https://git.kernel.org/stable/c/0eec592c6a7460ba795d7de29f3dc95cb5422e62
	https://git.kernel.org/stable/c/9462f4ca56e7d2430fdb6dcc8498244acbfc4489