CVE-2022-49366 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix reference count leak in smb_check_perm_dacl()
The issue happens in a specific path in smb_check_perm_dacl(). When "id" and "uid" have the same value, the function simply jumps out of the loop without decrementing the reference count of the object "posix_acls", which is increased by get_acl() earlier. This may result in memory leaks.
Fix it by decreasing the reference count of "posix_acls" before jumping to label "check_access_bits".
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Analysis
by VulDB Data Team • 04/15/2025
The vulnerability identified as CVE-2022-49366 resides within the Linux kernel's ksmbd subsystem, specifically affecting the smb_check_perm_dacl() function. This represents a classic reference counting error that can lead to memory leakage and potential resource exhaustion. The ksmbd component serves as a kernel module that provides SMB/CIFS file sharing capabilities, making it a critical component in enterprise network infrastructure where file sharing and access control are paramount. When the kernel processes access control list checks for SMB shares, this flaw manifests during specific conditional execution paths that are triggered by certain user identity mappings.
The technical flaw occurs in a conditional branch where the function evaluates whether the "id" and "uid" parameters have identical values. When this equality condition is met, the code executes an early exit from a loop structure without properly decrementing the reference count associated with the "posix_acls" object. This object is initially incremented through a call to get_acl() earlier in the function execution, establishing a reference count that should be balanced by a corresponding put_acl() or similar decrement operation. The absence of this decrement creates a reference count leak where the memory allocated for the ACL structure remains allocated even though it is no longer needed, leading to gradual memory consumption that could eventually impact system stability.
The operational impact of this vulnerability extends beyond simple memory leakage to potentially affect system availability and performance. In environments where ksmbd is heavily utilized for file sharing operations, particularly in high-throughput scenarios with frequent access control checks, the accumulation of leaked references can lead to memory exhaustion over time. This type of resource leak could enable denial of service conditions where legitimate system resources become unavailable due to memory constraints. The vulnerability is particularly concerning in enterprise environments where SMB shares are extensively used for data access and collaboration, as it could be exploited by attackers to consume system resources gradually until system performance degrades or crashes occur.
This vulnerability maps directly to CWE-404, which describes improper resource management or resource leaks in software systems. The flaw demonstrates poor adherence to reference counting principles that are fundamental to memory management in kernel space. From an ATT&CK perspective, this vulnerability could be leveraged as part of a resource exhaustion attack pattern, potentially serving as a stepping stone for more sophisticated exploitation techniques. The fix implemented addresses the specific path by ensuring that the reference count is properly decremented before jumping to the designated label, maintaining the integrity of the reference counting mechanism. This remediation follows established kernel development practices for managing reference-counted objects and aligns with the broader security principles of preventing resource leaks that could be exploited for denial of service or other malicious purposes. The fix demonstrates proper defensive programming techniques that ensure all code paths properly balance resource allocation and deallocation operations, thereby maintaining system stability and preventing the accumulation of leaked resources that could compromise system integrity.