CVE-2021-47250 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
net: ipv4: fix memory leak in netlbl_cipsov4_add_std
Reported by syzkaller: BUG: memory leak unreferenced object 0xffff888105df7000 (size 64): comm "syz-executor842", pid 360, jiffies 4294824824 (age 22.546s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [] kmalloc include/linux/slab.h:590 [inline]
[] kzalloc include/linux/slab.h:720 [inline]
[] netlbl_cipsov4_add_std net/netlabel/netlabel_cipso_v4.c:145 [inline]
[] netlbl_cipsov4_add+0x390/0x2340 net/netlabel/netlabel_cipso_v4.c:416
[] genl_family_rcv_msg_doit.isra.0+0x20e/0x320 net/netlink/genetlink.c:739
[] genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
[] genl_rcv_msg+0x2bf/0x4f0 net/netlink/genetlink.c:800
[] netlink_rcv_skb+0x134/0x3d0 net/netlink/af_netlink.c:2504
[] genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
[] netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
[] netlink_unicast+0x4a0/0x6a0 net/netlink/af_netlink.c:1340
[] netlink_sendmsg+0x789/0xc70 net/netlink/af_netlink.c:1929
[] sock_sendmsg_nosec net/socket.c:654 [inline]
[] sock_sendmsg+0x139/0x170 net/socket.c:674
[] ____sys_sendmsg+0x658/0x7d0 net/socket.c:2350
[] ___sys_sendmsg+0xf8/0x170 net/socket.c:2404
[] __sys_sendmsg+0xd3/0x190 net/socket.c:2433
[] do_syscall_64+0x37/0x90 arch/x86/entry/common.c:47
[] entry_SYSCALL_64_after_hwframe+0x44/0xae
The memory of doi_def->map.std pointing is allocated in netlbl_cipsov4_add_std, but no place has freed it. It should be freed in cipso_v4_doi_free which frees the cipso DOI resource.
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability identified as CVE-2021-47250 represents a memory leak within the Linux kernel's networking stack, specifically affecting the NetLabel CIPSO (Common IP Security Option) implementation for IPv4. This flaw resides in the netlbl_cipsov4_add_std function located in net/netlabel/netlabel_cipso_v4.c, where memory allocated for the doi_def->map.std structure is not properly released during cleanup operations. The issue was discovered through automated testing using syzkaller, a powerful fuzzer designed to identify kernel-level vulnerabilities. The memory leak manifests when the kernel processes CIPSO protocol messages through the Generic Netlink (genl) interface, which handles network configuration and management operations. The allocation occurs during the processing of network labeling operations, but subsequent cleanup routines fail to properly free the allocated memory, leading to a gradual accumulation of unreferenced memory blocks that cannot be reclaimed by the system's memory management subsystem.
The technical root cause of this vulnerability stems from improper memory management within the CIPSO DOI (Domain of Interpretation) resource cleanup function. When the kernel processes incoming CIPSO messages through the netlbl_cipsov4_add_std function, it allocates memory for the standard mapping structure (doi_def->map.std) to store security label information. However, the cipso_v4_doi_free function, which is responsible for releasing all memory associated with a CIPSO DOI resource, does not include code to free the memory allocated for the standard mapping structure. This creates a memory leak pattern where each processed CIPSO message results in 64 bytes of unreferenced memory that remains allocated until the system reboots or the kernel module is unloaded. The vulnerability is classified as a memory leak under CWE-401, which specifically addresses the failure to release memory resources, and represents a classic example of improper resource management that can lead to system instability and performance degradation over time.
The operational impact of this vulnerability extends beyond simple memory consumption, potentially leading to system resource exhaustion and denial of service conditions. The memory leak occurs during normal network operations when CIPSO security labels are processed, meaning that systems actively using NetLabel functionality for network security policies are at risk. Attackers could potentially exploit this vulnerability by repeatedly sending CIPSO protocol messages to trigger the memory leak, gradually consuming system memory resources until the system becomes unresponsive or crashes. The leak affects systems running Linux kernel versions that include the affected NetLabel implementation, particularly those implementing security policies that utilize CIPSO protocols for network access control. This vulnerability aligns with ATT&CK technique T1499.001, which covers resource exhaustion attacks, and could be leveraged by adversaries to perform persistent denial of service operations against network infrastructure.
Mitigation strategies for CVE-2021-47250 involve applying the official kernel patch that ensures proper memory cleanup in the cipso_v4_doi_free function. The fix requires adding code to explicitly free the doi_def->map.std memory allocation when cleaning up CIPSO DOI resources, thereby preventing the accumulation of unreferenced memory blocks. System administrators should prioritize updating their Linux kernel installations to versions that contain this patch, particularly in environments where NetLabel functionality is actively used for network security policies. Organizations should also implement monitoring solutions to detect unusual memory consumption patterns that might indicate the exploitation of this vulnerability. Additionally, network security teams should review their CIPSO-based security configurations and consider alternative network labeling approaches if the vulnerability cannot be immediately patched. The fix addresses the underlying CWE-401 memory leak issue and ensures proper resource management within the kernel's networking subsystem, preventing the gradual degradation of system performance through memory exhaustion attacks.