CVE-2026-98174 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix rlist race and missing initialization
TCP_Server_Info.rlist is allocated via kzalloc which zeros both ->next and ->prev to NULL instead of pointing to itself, making list_empty() always return false and list_add() dereference a NULL ->prev pointer.
Also, cifs_signal_cifsd_for_reconnect() can be called concurrently from multiple cifsd threads, allowing the same server's rlist node to be added twice into the local list, corrupting it.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified in the Linux kernel SMB client subsystem involves a critical initialization error and a concurrency flaw within the TCP_Server_Info structure, specifically affecting the remote list or rlist member. This issue stems from an incorrect memory allocation strategy where kzalloc is utilized to initialize the data structures associated with server connections. While kzalloc effectively zeroes out allocated memory, setting pointer fields such as next and prev to NULL, it fails to establish the self-referential pointers required for a properly initialized doubly linked list node. In standard Linux kernel programming practices using the list_head structure, an empty list node must point its own previous and next entries back to itself rather than null values. This deviation from expected initialization protocols fundamentally breaks the integrity of the linked list management functions that rely on these pointer relationships to determine emptiness or traverse nodes safely.
The immediate technical consequence of this improper initialization is a failure in the list_empty() function, which will consistently return false because it checks if the next and previous pointers point back to the head node rather than verifying null conditions as might be expected in other contexts. More critically, when operations such as list_add are performed on these improperly initialized nodes, the kernel attempts to dereference a NULL prev pointer during the insertion process. This action triggers an invalid memory access event, typically resulting in a kernel panic or system crash due to a NULL pointer dereference exception. Such instability compromises the reliability of the SMB client functionality and can lead to denial of service conditions for systems relying on this network file sharing protocol stack.
Beyond the initialization flaw, there exists a significant race condition within the cifs_signal_cifsd_for_reconnect function. This routine is designed to signal connection reconstruction needs but lacks adequate synchronization mechanisms when invoked concurrently by multiple cifsd threads. The absence of proper locking allows identical server remote list nodes to be inserted into local lists more than once simultaneously. This concurrent modification leads to structural corruption of the linked list, creating circular references or broken chains that further exacerbate instability during traversal and deletion operations. Such race conditions are particularly dangerous in multi-threaded environments where timing dependencies can lead to unpredictable behavior and data structure integrity loss.
From a classification perspective, this vulnerability aligns with CWE-908, which covers the use of uninitialized resource, specifically regarding improper initialization of linked list pointers that leads to null pointer dereferences. Additionally, the race condition aspect relates closely to CWE-362, indicating concurrent execution issues where shared resources are accessed without proper synchronization controls. In terms of attack vectors and behavioral patterns, this scenario reflects elements found in ATT&CK technique T1499, specifically endpoint denial of service through resource exhaustion or instability caused by software flaws that allow attackers or automated processes to trigger crashes via malformed state transitions or concurrent access patterns.
Mitigation strategies for this vulnerability primarily involve applying the upstream kernel patches provided by Linux distribution maintainers which correct the initialization logic and introduce appropriate locking mechanisms around critical sections involving server list modifications. Administrators should ensure their systems are updated with the latest stable kernel versions that include these fixes. For environments where immediate patching is not feasible, monitoring system logs for NULL pointer dereference errors or unexpected SMB client disconnections can help identify potential exploitation attempts or instability events. Furthermore, reviewing application code that interacts directly with low-level network structures to ensure proper synchronization primitives are used when managing shared server state information remains a best practice for preventing similar concurrency-related defects in custom implementations of the CIFS protocol stack.