CVE-2024-50073 in Linux
Summary
by MITRE • 10/29/2024
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: 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.
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Analysis
by VulDB Data Team • 08/21/2025
The vulnerability CVE-2024-50073 resides within the Linux kernel's tty subsystem, specifically in the n_gsm driver responsible for handling GSM (Global System for Mobile Communications) multiplexing operations. This issue manifests as a use-after-free condition in the gsm_cleanup_mux function, which occurs when multiple threads attempt to access and manipulate shared data structures without proper synchronization. The flaw is triggered during ioctl operations that manage GSM communication channels, where memory allocated for GSM messages on transmission control and data lists becomes prematurely freed while other threads may still reference it.
The technical root cause stems from insufficient locking mechanisms within the GSM multiplexer implementation. When gsm_cleanup_mux executes, it attempts to free memory structures containing gsm_msg objects that are simultaneously being accessed by other threads through various ioctl calls. The kernel's memory sanitizer (KASAN) detects this violation by identifying a read operation of size 8 occurring at address ff ff 88 81 5f e9 9c 00, which corresponds to memory that was previously freed by a different thread. This race condition arises because the code lacks proper serialization when accessing the tx_ctrl_list and tx_data_list structures, allowing concurrent access patterns that lead to memory corruption.
The operational impact of this vulnerability is significant as it can be exploited to achieve arbitrary code execution within the kernel context, potentially leading to privilege escalation or system compromise. An attacker could craft malicious ioctl commands that trigger the race condition, causing the kernel to execute code from freed memory locations. The call trace shows the vulnerability propagates through multiple kernel subsystems including the scheduler, workqueue processing, and tty layer management, demonstrating how a flaw in one component can cascade through the entire kernel execution flow. This aligns with CWE-416, which describes use-after-free vulnerabilities where memory is accessed after it has been freed.
Mitigation strategies should focus on implementing proper locking mechanisms around the shared data structures in the gsm_mux implementation. The fix requires protecting access to tx_ctrl_list and tx_data_list through the existing gsm tx lock as suggested in the analysis, ensuring that no thread can free memory while another thread accesses it. Additionally, kernel developers should consider implementing more robust memory management practices such as reference counting for shared objects or using lock-free data structures where appropriate. The solution must align with ATT&CK framework's privilege escalation techniques by ensuring proper kernel memory protection and preventing unauthorized access patterns that could lead to system compromise. Regular kernel updates and security audits should be performed to identify similar race conditions in other kernel subsystems that may present analogous vulnerabilities.