CVE-2022-50648
Description
In the Linux kernel, the following vulnerability has been resolved:
ftrace: Fix recursive locking direct_mutex in ftrace_modify_direct_caller
Naveen reported recursive locking of direct_mutex with sample ftrace-direct-modify.ko:
[ 74.762406] WARNING: possible recursive locking detected [ 74.762887] 6.0.0-rc6+ #33 Not tainted [ 74.763216] -------------------------------------------- [ 74.763672] event-sample-fn/1084 is trying to acquire lock: [ 74.764152] ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \ register_ftrace_function+0x1f/0x180 [ 74.764922] [ 74.764922] but task is already holding lock: [ 74.765421] ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \ modify_ftrace_direct+0x34/0x1f0 [ 74.766142] [ 74.766142] other info that might help us debug this: [ 74.766701] Possible unsafe locking scenario: [ 74.766701] [ 74.767216] CPU0 [ 74.767437] ---- [ 74.767656] lock(direct_mutex); [ 74.767952] lock(direct_mutex); [ 74.768245] [ 74.768245] * DEADLOCK * [ 74.768245] [ 74.768750] May be due to missing lock nesting notation [ 74.768750] [ 74.769332] 1 lock held by event-sample-fn/1084: [ 74.769731] #0: ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \ modify_ftrace_direct+0x34/0x1f0 [ 74.770496] [ 74.770496] stack backtrace: [ 74.770884] CPU: 4 PID: 1084 Comm: event-sample-fn Not tainted ... [ 74.771498] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ... [ 74.772474] Call Trace: [ 74.772696] [ 74.772896] dump_stack_lvl+0x44/0x5b [ 74.773223] __lock_acquire.cold.74+0xac/0x2b7 [ 74.773616] lock_acquire+0xd2/0x310 [ 74.773936] ? register_ftrace_function+0x1f/0x180 [ 74.774357] ? lock_is_held_type+0xd8/0x130 [ 74.774744] ? my_tramp2+0x11/0x11 [ftrace_direct_modify] [ 74.775213] __mutex_lock+0x99/0x1010 [ 74.775536] ? register_ftrace_function+0x1f/0x180 [ 74.775954] ? slab_free_freelist_hook.isra.43+0x115/0x160 [ 74.776424] ? ftrace_set_hash+0x195/0x220 [ 74.776779] ? register_ftrace_function+0x1f/0x180 [ 74.777194] ? kfree+0x3e1/0x440 [ 74.777482] ? my_tramp2+0x11/0x11 [ftrace_direct_modify] [ 74.777941] ? __schedule+0xb40/0xb40 [ 74.778258] ? register_ftrace_function+0x1f/0x180 [ 74.778672] ? my_tramp1+0xf/0xf [ftrace_direct_modify] [ 74.779128] register_ftrace_function+0x1f/0x180 [ 74.779527] ? ftrace_set_filter_ip+0x33/0x70 [ 74.779910] ? __schedule+0xb40/0xb40 [ 74.780231] ? my_tramp1+0xf/0xf [ftrace_direct_modify] [ 74.780678] ? my_tramp2+0x11/0x11 [ftrace_direct_modify] [ 74.781147] ftrace_modify_direct_caller+0x5b/0x90 [ 74.781563] ? 0xffffffffa0201000 [ 74.781859] ? my_tramp1+0xf/0xf [ftrace_direct_modify] [ 74.782309] modify_ftrace_direct+0x1b2/0x1f0 [ 74.782690] ? __schedule+0xb40/0xb40 [ 74.783014] ? simple_thread+0x2a/0xb0 [ftrace_direct_modify] [ 74.783508] ? __schedule+0xb40/0xb40 [ 74.783832] ? my_tramp2+0x11/0x11 [ftrace_direct_modify] [ 74.784294] simple_thread+0x76/0xb0 [ftrace_direct_modify] [ 74.784766] kthread+0xf5/0x120 [ 74.785052] ? kthread_complete_and_exit+0x20/0x20 [ 74.785464] ret_from_fork+0x22/0x30 [ 74.785781]
Fix this by using register_ftrace_function_nolock in ftrace_modify_direct_caller.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
CVE-2022-50648 is a recursive locking vulnerability in the Linux kernel's ftrace subsystem that can cause a deadlock when modifying direct function callers.
CVE-2022-50648 describes a recursive locking issue in the Linux kernel's ftrace subsystem, specifically in the function ftrace_modify_direct_caller. The problem occurs when modify_ftrace_direct acquires the direct_mutex and then calls register_ftrace_function, which attempts to acquire the same mutex again, leading to a recursive lock [1]. This results in a kernel warning about a possible deadlock, as reported by Naveen with the ftrace-direct-modify sample kernel module [1].
The vulnerability is exploitable when an unprivileged user or a kernel module triggers the ftrace direct modification path, causing a recursive mutex lock [1]. The attack surface is limited to systems where ftrace direct functionality is enabled and a caller can invoke both modify_ftrace_direct and register_ftrace_function in sequence [1]. No authentication is required beyond the ability to load or trigger the relevant kernel code, which in this case was demonstrated with a test module [1].
If exploited, the recursive locking can cause a kernel deadlock, leading to a denial of service (DoS) condition [1]. The system may become unresponsive, requiring a reboot to recover. An attacker with the ability to trigger this code path could cause a local system hang [1].
The fix for this issue was included in the Linux kernel stable tree via commit 9d2ce78ddcee159eb6a97449e9c68b6d60b9cec4 [1]. Users should apply the latest kernel updates to mitigate this vulnerability.
AI Insight generated on May 19, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
2Patches
22482eacb685b9d2ce78ddceeVulnerability mechanics
Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
2News mentions
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