CVE-2023-52757 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix potential deadlock when releasing mids
All release_mid() callers seem to hold a reference of @mid so there is no need to call kref_put(&mid->refcount, __release_mid) under @server->mid_lock spinlock. If they don't, then an use-after-free bug would have occurred anyways.
By getting rid of such spinlock also fixes a potential deadlock as shown below
CPU 0 CPU 1 ------------------------------------------------------------------ cifs_demultiplex_thread() cifs_debug_data_proc_show() release_mid() spin_lock(&server->mid_lock); spin_lock(&cifs_tcp_ses_lock) spin_lock(&server->mid_lock) __release_mid() smb2_find_smb_tcon() spin_lock(&cifs_tcp_ses_lock) *deadlock*
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Analysis
by VulDB Data Team • 01/07/2025
The vulnerability CVE-2023-52757 represents a critical deadlock condition within the Linux kernel's SMB client implementation that arises from improper handling of mid (message identifier) reference counting and locking mechanisms. This flaw exists in the cifs (Common Internet File System) subsystem which provides SMB/CIFS file sharing capabilities to Linux systems. The issue manifests when the release_mid() function attempts to release message identifiers while holding the server->mid_lock spinlock, creating a circular dependency that can lead to system-wide deadlock conditions.
The technical root cause of this vulnerability stems from the improper synchronization between multiple spinlocks within the SMB client code path. When cifs_demultiplex_thread() calls release_mid(), it acquires the server->mid_lock spinlock before invoking __release_mid(), which subsequently calls smb2_find_smb_tcon() and attempts to acquire the cifs_tcp_ses_lock. Meanwhile, another code path such as cifs_debug_data_proc_show() may already hold the cifs_tcp_ses_lock and then attempt to acquire the server->mid_lock, creating a classic deadlock scenario. This pattern violates fundamental concurrency principles and violates the principle of lock ordering that is essential for preventing deadlock conditions in concurrent systems.
The operational impact of this vulnerability extends beyond simple system hang conditions as it can render entire file sharing services unavailable and potentially cause complete system lockups. Systems utilizing SMB client functionality for file access, network drives, or distributed computing environments become vulnerable to denial of service attacks that can persist until system reboot. The vulnerability affects any Linux kernel version that includes the affected SMB client implementation, making it particularly concerning for enterprise environments where SMB services are heavily utilized for data sharing and collaboration. The use of spinlocks in this context violates the common security principle of avoiding lock contention in kernel space, as outlined in the CWE-362 category for concurrent execution issues.
Mitigation strategies for this vulnerability should focus on immediate kernel updates to versions containing the patched code that removes the unnecessary spinlock acquisition during mid release operations. System administrators should prioritize patching affected systems, particularly those running SMB clients in production environments. Additionally, monitoring for potential deadlock conditions and implementing proper lock ordering policies can help prevent similar issues from occurring in other kernel subsystems. The fix implemented addresses the specific deadlock scenario by removing the spin_lock(&server->mid_lock) call within the release_mid() function, thereby eliminating the circular dependency that led to the system-wide hang condition. This solution aligns with ATT&CK technique T1499.004 for network disruption and represents a fundamental correction to kernel concurrency management practices that should be considered when implementing similar locking mechanisms in security-critical systems.