CVE-2022-48751 in Linux
Summary
by MITRE • 06/20/2024
In the Linux kernel, the following vulnerability has been resolved:
net/smc: Transitional solution for clcsock race issue
We encountered a crash in smc_setsockopt() and it is caused by accessing smc->clcsock after clcsock was released.
BUG: kernel NULL pointer dereference, address: 0000000000000020 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 1 PID: 50309 Comm: nginx Kdump: loaded Tainted: G E 5.16.0-rc4+ #53 RIP: 0010:smc_setsockopt+0x59/0x280 [smc]
Call Trace: __sys_setsockopt+0xfc/0x190 __x64_sys_setsockopt+0x20/0x30 do_syscall_64+0x34/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f16ba83918e
This patch tries to fix it by holding clcsock_release_lock and checking whether clcsock has already been released before access.
In case that a crash of the same reason happens in smc_getsockopt() or smc_switch_to_fallback(), this patch also checkes smc->clcsock in them too. And the caller of smc_switch_to_fallback() will identify whether fallback succeeds according to the return value.
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Analysis
by VulDB Data Team • 01/07/2025
The vulnerability described in CVE-2022-48751 represents a critical race condition within the Linux kernel's SMC (Scalable Meta Cluster) networking subsystem. This issue manifests as a kernel NULL pointer dereference occurring in the smc_setsockopt() function when attempting to access the clcsock member after it has already been released. The vulnerability stems from insufficient synchronization mechanisms during the lifecycle management of SMC connections, specifically around the clcsock resource handling. The crash pattern indicates a classic race condition where one thread accesses a resource that another thread has simultaneously released, leading to a kernel panic and system instability. The error trace shows the fault occurring at RIP: 0010:smc_setsockopt+0x59/0x280 [smc] with a supervisor read access to address 0000000000000020, clearly indicating a null pointer dereference in kernel space.
The technical flaw involves improper locking mechanisms and resource management within the SMC subsystem's socket option handling functions. The vulnerability specifically targets the clcsock (connection listener socket) which is accessed without proper synchronization checks, creating a window where the socket structure may be freed while still being referenced. This race condition affects not only the smc_setsockopt() function but also extends to smc_getsockopt() and smc_switch_to_fallback() functions, suggesting a systemic issue in how the SMC subsystem manages its connection resources. The patch implements a transitional solution by introducing clcsock_release_lock and adding checks to verify whether clcsock has been released before accessing it, following the established pattern of defensive programming in kernel space. The vulnerability aligns with CWE-362, which describes a race condition in kernel-level code where concurrent access to shared resources leads to unpredictable behavior and potential system crashes.
The operational impact of this vulnerability is significant, particularly in environments where the SMC subsystem is actively used for high-performance networking applications. The vulnerability can lead to complete system crashes, requiring system restarts and potentially causing service disruption in production environments. The specific mention of nginx in the crash trace indicates that web servers utilizing SMC for network optimization are at risk, though the vulnerability affects the underlying kernel networking stack rather than specific applications. This type of kernel-level race condition represents a serious security concern because it can potentially be exploited to cause denial of service attacks or, in more sophisticated scenarios, could provide a foothold for privilege escalation. The vulnerability affects kernel versions including 5.16.0-rc4 and later, making it relevant to modern Linux systems that support SMC networking protocols. The patch addresses the issue by implementing proper locking mechanisms and conditional checks that prevent access to freed resources, following ATT&CK technique T1499.004 for system binary permissions and maintaining kernel integrity through proper resource management.
The fix implemented for CVE-2022-48751 demonstrates a transitional approach to resolving the race condition by introducing proper locking mechanisms and access validation before resource usage. The patch ensures that clcsock_release_lock is held during access checks and implements validation in multiple functions to prevent similar issues across the SMC subsystem. This approach aligns with kernel security best practices for managing shared resources in concurrent environments. The solution also includes return value handling for smc_switch_to_fallback() to allow callers to properly identify whether fallback operations succeed, providing better error recovery and system stability. Organizations should prioritize applying this patch to systems running affected kernel versions, particularly those utilizing SMC networking features for high-performance applications. The vulnerability underscores the importance of proper synchronization in kernel space and highlights the need for comprehensive testing of concurrent access patterns in networking subsystems. This type of vulnerability serves as a reminder of the critical nature of kernel-level resource management and the potential for seemingly simple race conditions to cause catastrophic system failures.