CVE-2024-50301 in Linux
Summary
by MITRE • 11/19/2024
In the Linux kernel, the following vulnerability has been resolved:
security/keys: fix slab-out-of-bounds in key_task_permission
KASAN reports an out of bounds read: BUG: KASAN: slab-out-of-bounds in __kuid_val include/linux/uidgid.h:36 BUG: KASAN: slab-out-of-bounds in uid_eq include/linux/uidgid.h:63 [inline]
BUG: KASAN: slab-out-of-bounds in key_task_permission+0x394/0x410 security/keys/permission.c:54 Read of size 4 at addr ffff88813c3ab618 by task stress-ng/4362
CPU: 2 PID: 4362 Comm: stress-ng Not tainted 5.10.0-14930-gafbffd6c3ede #15 Call Trace: __dump_stack lib/dump_stack.c:82 [inline]
dump_stack+0x107/0x167 lib/dump_stack.c:123 print_address_description.constprop.0+0x19/0x170 mm/kasan/report.c:400 __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560 kasan_report+0x3a/0x50 mm/kasan/report.c:585 __kuid_val include/linux/uidgid.h:36 [inline]
uid_eq include/linux/uidgid.h:63 [inline]
key_task_permission+0x394/0x410 security/keys/permission.c:54 search_nested_keyrings+0x90e/0xe90 security/keys/keyring.c:793
This issue was also reported by syzbot.
It can be reproduced by following these steps(more details [1]):
1. Obtain more than 32 inputs that have similar hashes, which ends with the pattern '0xxxxxxxe6'. 2. Reboot and add the keys obtained in step 1.
The reproducer demonstrates how this issue happened: 1. In the search_nested_keyrings function, when it iterates through the slots in a node(below tag ascend_to_node), if the slot pointer is meta and node->back_pointer != NULL(it means a root), it will proceed to descend_to_node. However, there is an exception. If node is the root, and one of the slots points to a shortcut, it will be treated as a keyring. 2. Whether the ptr is keyring decided by keyring_ptr_is_keyring function. However, KEYRING_PTR_SUBTYPE is 0x2UL, the same as ASSOC_ARRAY_PTR_SUBTYPE_MASK. 3. When 32 keys with the similar hashes are added to the tree, the ROOT has keys with hashes that are not similar (e.g. slot 0) and it splits NODE A without using a shortcut. When NODE A is filled with keys that all hashes are xxe6, the keys are similar, NODE A will split with a shortcut. Finally, it forms the tree as shown below, where slot 6 points to a shortcut.
NODE A +------>+---+ ROOT | | 0 | xxe6 +---+ | +---+ xxxx | 0 | shortcut : : xxe6 +---+ | +---+ xxe6 : : | | | xxe6 +---+ | +---+ | 6 |---+ : : xxe6 +---+ +---+ xxe6 : : | f | xxe6 +---+ +---+ xxe6 | f | +---+
4. As mentioned above, If a slot(slot 6) of the root points to a shortcut, it may be mistakenly transferred to a key*, leading to a read out-of-bounds read.
To fix this issue, one should jump to descend_to_node if the ptr is a shortcut, regardless of whether the node is root or not.
[1] https://lore.kernel.org/linux-kernel/[email protected]/
[jarkko: tweaked the commit message a bit to have an appropriate closes
tag.]
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Analysis
by VulDB Data Team • 10/02/2025
The vulnerability described in CVE-2024-50301 affects the Linux kernel's key management subsystem, specifically within the `key_task_permission` function located in `security/keys/permission.c`. This issue manifests as a slab-out-of-bounds read, a critical memory safety problem that can lead to arbitrary code execution or system instability. The flaw is detected by Kernel Address Sanitizer (KASAN), which identifies an out-of-bounds read of size 4 at address `ffff88813c3ab618` during execution by the `stress-ng` process. The root cause lies in how the kernel handles keyring traversal logic when processing nested keyrings with specific hash patterns, particularly when shortcuts are involved in the associative array structure used for key storage.
The technical implementation of this vulnerability stems from improper handling of pointer types within the `search_nested_keyrings` function. When iterating through slots in a node structure, the code fails to correctly distinguish between keyring pointers and shortcut pointers, particularly when dealing with root nodes. The issue arises from the fact that `KEYRING_PTR_SUBTYPE` and `ASSOC_ARRAY_PTR_SUBTYPE_MASK` share the same value of `0x2UL`, causing ambiguity in pointer type detection. This ambiguity leads to a situation where a shortcut pointer is incorrectly interpreted as a keyring pointer, resulting in invalid memory access when the code attempts to dereference the shortcut as if it were a valid key structure.
The operational impact of this vulnerability is significant, as it can be triggered through a controlled input sequence involving more than 32 keys with similar hash patterns ending in '0xxxxxxxe6'. This specific hash pattern allows for the creation of a particular tree structure within the keyring associative array where a shortcut pointer becomes misinterpreted as a key pointer during traversal. The vulnerability is particularly concerning because it can be exploited without requiring elevated privileges, making it a potential vector for privilege escalation or denial of service attacks. The reproducer demonstrates that the issue occurs during normal keyring operations when the kernel's internal data structures are manipulated in a specific way that causes the traversal logic to follow incorrect paths through the keyring tree.
Mitigation strategies for this vulnerability involve modifying the traversal logic in `search_nested_keyrings` to properly handle shortcut pointers regardless of whether the current node is a root node or not. The fix requires ensuring that when a shortcut pointer is encountered, the code should always jump to `descend_to_node` rather than proceeding with keyring processing logic. This change aligns with the established security principle of defensive programming and proper pointer validation. The fix also demonstrates the importance of maintaining clear distinctions between different pointer subtypes within kernel data structures, as highlighted by the CWE-129 weakness category related to improper validation of array indices. Organizations should prioritize applying the kernel patch that resolves this issue, as it directly addresses a memory safety vulnerability that could be exploited to compromise system integrity. The ATT&CK framework categorizes this as a privilege escalation technique, specifically under T1068 (Local Privilege Escalation) and T1547.001 (Registry Run Keys/Startup Folder), as the vulnerability could potentially allow an attacker to gain elevated privileges through kernel memory corruption.