CVE-2024-44992 in Linux
Summary
by MITRE • 09/04/2024
In the Linux kernel, the following vulnerability has been resolved:
smb/client: avoid possible NULL dereference in cifs_free_subrequest()
Clang static checker (scan-build) warning: cifsglob.h:line 890, column 3 Access to field 'ops' results in a dereference of a null pointer.
Commit 519be989717c ("cifs: Add a tracepoint to track credits involved in R/W requests") adds a check for 'rdata->server', and let clang throw this warning about NULL dereference.
When 'rdata->credits.value != 0 && rdata->server == NULL' happens, add_credits_and_wake_if() will call rdata->server->ops->add_credits(). This will cause NULL dereference problem. Add a check for 'rdata->server' to avoid NULL dereference.
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Analysis
by VulDB Data Team • 09/07/2024
The vulnerability CVE-2024-44992 represents a critical null pointer dereference issue within the Linux kernel's CIFS (Common Internet File System) client implementation. This flaw exists in the cifs_free_subrequest() function where the kernel attempts to access the 'ops' field of a server structure without proper validation of the server pointer. The issue was identified through static code analysis using Clang's scan-build tool which flagged a potential null pointer dereference at line 890 in cifsglob.h. The vulnerability stems from a recent commit 519be989717c that introduced tracepoints for tracking credits in read/write requests but inadvertently created a path where the server pointer could be null while credits are still being processed.
The technical execution path leading to this vulnerability involves the add_credits_and_wake_if() function which is called when rdata->credits.value is non-zero but rdata->server is NULL. Under these conditions, the code attempts to invoke rdata->server->ops->add_credits() without validating that rdata->server is a valid pointer. This null pointer dereference occurs because the new tracepoint functionality added in the commit did not account for scenarios where server connections might be in a transitional state or have been disconnected while credit operations are still pending. The flaw represents a classic CWE-476 Null Pointer Dereference vulnerability, where the absence of proper null checks leads to system crashes or potential privilege escalation opportunities.
The operational impact of this vulnerability extends beyond simple system crashes, as it can lead to denial of service conditions that affect file sharing operations across networked systems. When the CIFS client encounters a null server pointer during credit management operations, the kernel will panic and terminate, potentially affecting all network file access for systems using CIFS mounts. This vulnerability particularly impacts enterprise environments that rely heavily on network file systems, as it can cause cascading failures when multiple concurrent file operations occur during server disconnections or connection resets. The issue is especially concerning in high-availability environments where uninterrupted file access is critical for business operations, as it can trigger unexpected system reboots or service interruptions that may go unnoticed until system monitoring detects the failures.
Mitigation strategies for CVE-2024-44992 should focus on applying the immediate kernel patch that adds proper null pointer validation before accessing server operations. System administrators should prioritize updating kernel versions to include the fix from commit 519be989717c, which introduces the necessary check for rdata->server before attempting to dereference the ops field. Organizations should implement monitoring solutions to detect potential null pointer dereference conditions in their network file systems and establish automated alerting for kernel panic events related to CIFS operations. Additionally, implementing proper connection health checks and graceful degradation mechanisms can help minimize the impact of this vulnerability by preventing operations that might trigger the null pointer condition. This vulnerability aligns with ATT&CK technique T1489 System Network Configuration Discovery and T1562 Impair Defenses, as it represents a kernel-level attack vector that can disable network file access capabilities and potentially provide attackers with opportunities to escalate privileges through system instability.