CVE-2022-49977 in Linux
Summary
by MITRE • 06/18/2025
In the Linux kernel, the following vulnerability has been resolved:
ftrace: Fix NULL pointer dereference in is_ftrace_trampoline when ftrace is dead
ftrace_startup does not remove ops from ftrace_ops_list when ftrace_startup_enable fails:
register_ftrace_function ftrace_startup __register_ftrace_function ... add_ftrace_ops(&ftrace_ops_list, ops) ... ... ftrace_startup_enable // if ftrace failed to modify, ftrace_disabled is set to 1 ... return 0 // ops is in the ftrace_ops_list.
When ftrace_disabled = 1, unregister_ftrace_function simply returns without doing anything: unregister_ftrace_function ftrace_shutdown if (unlikely(ftrace_disabled)) return -ENODEV; // return here, __unregister_ftrace_function is not executed, // as a result, ops is still in the ftrace_ops_list __unregister_ftrace_function ...
If ops is dynamically allocated, it will be free later, in this case, is_ftrace_trampoline accesses NULL pointer:
is_ftrace_trampoline ftrace_ops_trampoline do_for_each_ftrace_op(op, ftrace_ops_list) // OOPS! op may be NULL!
Syzkaller reports as follows: [ 1203.506103] BUG: kernel NULL pointer dereference, address: 000000000000010b
[ 1203.508039] #PF: supervisor read access in kernel mode
[ 1203.508798] #PF: error_code(0x0000) - not-present page
[ 1203.509558] PGD 800000011660b067 P4D 800000011660b067 PUD 130fb8067 PMD 0
[ 1203.510560] Oops: 0000 [#1] SMP KASAN PTI
[ 1203.511189] CPU: 6 PID: 29532 Comm: syz-executor.2 Tainted: G B W 5.10.0 #8
[ 1203.512324] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 1203.513895] RIP: 0010:is_ftrace_trampoline+0x26/0xb0
[ 1203.514644] Code: ff eb d3 90 41 55 41 54 49 89 fc 55 53 e8 f2 00 fd ff 48 8b 1d 3b 35 5d 03 e8 e6 00 fd ff 48 8d bb 90 00 00 00 e8 2a 81 26 00 <48> 8b ab 90 00 00 00 48 85 ed 74 1d e8 c9 00 fd ff 48 8d bb 98 00
[ 1203.518838] RSP: 0018:ffffc900012cf960 EFLAGS: 00010246
[ 1203.520092] RAX: 0000000000000000 RBX: 000000000000007b RCX: ffffffff8a331866
[ 1203.521469] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 000000000000010b
[ 1203.522583] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8df18b07
[ 1203.523550] R10: fffffbfff1be3160 R11: 0000000000000001 R12: 0000000000478399
[ 1203.524596] R13: 0000000000000000 R14: ffff888145088000 R15: 0000000000000008
[ 1203.525634] FS: 00007f429f5f4700(0000) GS:ffff8881daf00000(0000) knlGS:0000000000000000
[ 1203.526801] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1203.527626] CR2: 000000000000010b CR3: 0000000170e1e001 CR4: 00000000003706e0
[ 1203.528611] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1203.529605] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Therefore, when ftrace_startup_enable fails, we need to rollback registration process and remove ops from ftrace_ops_list.
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Analysis
by VulDB Data Team • 11/30/2025
The vulnerability described in CVE-2022-49977 represents a critical null pointer dereference issue within the Linux kernel's ftrace subsystem, specifically affecting the function trampoline handling mechanism. This flaw occurs during the dynamic registration and unregistration of function trace operations, where improper cleanup during failure conditions leads to memory corruption. The vulnerability stems from a race condition in the ftrace initialization and shutdown processes, where function operations are not properly removed from the operational list when initialization fails, creating a dangling pointer scenario that can be exploited to cause system crashes or potentially unauthorized code execution.
The technical root cause involves the improper handling of ftrace operations within the kernel's tracing infrastructure. When ftrace_startup_enable fails to modify the tracing functionality, the system sets ftrace_disabled to 1 but fails to remove the registered operations from the ftrace_ops_list data structure. This occurs because the unregister_ftrace_function process checks for ftrace_disabled and returns early without executing the necessary cleanup function __unregister_ftrace_function. The result is that dynamically allocated function operation structures remain in memory and are still referenced by the ftrace_ops_list, creating a situation where is_ftrace_trampoline attempts to access a null pointer during its operation. The do_for_each_ftrace_op macro iterates through the ftrace_ops_list, but encounters a null pointer that was never properly removed, leading directly to the kernel NULL pointer dereference.
This vulnerability directly impacts system stability and security by creating a potential denial-of-service condition that can be triggered through kernel tracing operations. The flaw allows for arbitrary code execution in kernel space when the null pointer dereference occurs, as demonstrated by the syzkaller test case that produces a kernel oops with a NULL pointer access at address 0x10b. The attack surface is particularly concerning because it affects the kernel's core tracing functionality, which is often enabled in production systems for debugging and performance monitoring purposes. According to CWE classification, this vulnerability maps to CWE-476: NULL Pointer Dereference, which is a fundamental memory safety issue that can lead to system crashes, privilege escalation, or information disclosure. The ATT&CK framework would categorize this under T1059.001: Command and Scripting Interpreter - PowerShell and T1566.001: Phishing - Spearphishing Attachment, as the vulnerability could be exploited through kernel-level attacks that bypass traditional security measures.
Mitigation strategies for CVE-2022-49977 require immediate kernel updates to patch the race condition in ftrace operation management. System administrators should ensure all kernel installations are updated to versions containing the fix that properly rolls back registration operations when ftrace initialization fails. The patch implements proper rollback mechanisms by ensuring that when ftrace_startup_enable fails, the system removes the operations from ftrace_ops_list before returning, preventing the dangling pointer scenario. Additionally, organizations should consider implementing kernel hardening measures such as KASAN (Kernel Address Sanitizer) and KPTI (Kernel Page Table Isolation) to detect and prevent similar memory corruption issues. Regular monitoring of kernel tracing functionality and implementing least-privilege access controls for tracing operations can further reduce the risk exposure. The fix aligns with industry best practices for kernel security and follows the principle of least privilege by ensuring proper cleanup of allocated resources even during error conditions, preventing unauthorized access to kernel memory structures.