CVE-2026-99224 in Linux
Summary
by MITRE • 11/02/2026
In the Linux kernel, the following vulnerability has been resolved:
keys: Protect the type name while describing a key
keyctl_describe_key() must keep the key type's name alive until kasprintf() has consumed it. The retained key reference keeps the key and its description alive, but does not pin the module providing its type. The name is passed to kasprintf() without holding key->sem.
kvasprintf() uses the saved name pointer in two formatting passes, with a GFP_KERNEL allocation between them. With AF_RXRPC=m, a task that passes View permission before type retirement can overlap a privileged module unload in this order:
1. KEYCTL_DESCRIBE looks up the key, saves key->type->name in the kasprintf() arguments and completes the first formatting pass. 2. While the formatter is delayed before its second pass, af_rxrpc_exit() calls unregister_key_type(), which removes the type from the registry and waits for key_gc_keytype(). 3. The collector takes key->sem for writing, retypes the retained key to key_type_dead and completes retirement. Unregistration and module exit return, allowing free_module() to release the type and name. 4. The formatter resumes its second pass and reads the saved name from released module storage, which can fault in string().
Hold key->sem for reading across kasprintf(). The collector then cannot retype the key or complete retirement until both formatting passes have finished. If retirement wins the lock first, formatting uses the core key_type_dead name instead. Release the semaphore immediately after kasprintf(), including on allocation failure, before copying to userspace.
Oops report as below:
BUG: unable to handle page fault for address: fffffbfff8054794 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page RIP: 0010:string+0x23f/0x470 Call Trace: vsnprintf+0x330/0x1110
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Analysis
by VulDB Data Team • 11/02/2026
The Linux kernel key management subsystem contains a race condition vulnerability within the keyctl_describe_key function that allows for use-after-free memory corruption. This flaw arises from an incorrect synchronization strategy when handling key type names during string formatting operations. Specifically, the code retains a reference to the key structure to keep its description alive but fails to pin the underlying kernel module that provides the specific key type implementation. Consequently, while the key object itself remains valid in memory, the module containing the static name strings associated with that key type can be unloaded and freed if no other references are held during critical formatting intervals.
The technical root cause lies in the interaction between kasprintf and concurrent module unloading operations. The kvasprintf function performs two separate formatting passes to construct the final string, allocating memory using GFP_KERNEL between these passes. This creates a window of vulnerability where a privileged task can trigger an AF_RXRPC module unload while the formatter is paused after its first pass but before completing the second. During this interval, the unregister_key_type routine removes the type from the registry and initiates retirement procedures. The key garbage collector subsequently acquires the write lock on key->sem to retype the retained key as dead, effectively finalizing the retirement process. This allows free_module to execute and release the memory containing the original type name string.
When the formatter resumes for its second pass, it attempts to read from the saved pointer that now points into freed module storage. Accessing this invalid memory address triggers a page fault in kernel mode, resulting in an out-of-bounds read or general protection fault as indicated by the BUG report showing supervisor read access errors within the string function. This vulnerability can lead to kernel crashes, denial of service, and potentially arbitrary code execution if an attacker can control the contents allocated at the freed memory address through careful heap grooming techniques. The issue is particularly relevant in configurations where AF_RXRPC is compiled as a loadable module rather than built into the kernel image.
To mitigate this vulnerability, developers must ensure that key->sem is held for reading across the entire duration of kasprintf operations. By holding this semaphore, the code prevents the collector from acquiring the write lock required to retype the key or complete retirement until both formatting passes have finished successfully. If a race condition occurs where retirement acquires the lock first, the system safely falls back to using the core key_type_dead name instead of accessing potentially freed memory. Furthermore, the semaphore should be released immediately after kasprintf completes, including in error paths such as allocation failures, before any data is copied to userspace. This ensures that synchronization primitives are not held longer than necessary while still protecting against the specific race condition during string construction.
From a standards perspective, this vulnerability maps directly to CWE-416 Use After Free, where memory is accessed after it has been freed due to improper lifecycle management of resources. The attack vector aligns with ATT&CK technique T1059 Command and Scripting Interpreter if the crash leads to system instability exploitable for denial of service, though primarily this represents a stability issue rather than direct exploitation for privilege escalation without additional heap spraying techniques. Proper synchronization using read-write locks is essential in kernel subsystems that interact with loadable modules to prevent dangling pointers during asynchronous operations like module unloading and garbage collection cycles.