CVE-2025-38527
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk33th percentile - higher than 33% of all known CVEs
Summary
A use-after-free vulnerability in the Linux kernel's SMB client (cifs) was found in cifs_oplock_break() due to a race condition during unmount. The cinode structure is accessed after the superblock is released, leading to memory corruption.
Risk Assessment
An attacker could exploit this race condition to escalate privileges or cause a kernel panic by triggering the vulnerability during SMB share disconnection.
Recommendation
Apply the Linux kernel patch that holds an extra superblock reference during oplock break operations. Update the kernel to a fixed version.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix use-after-free in cifs_oplock_break A race condition can occur in cifs_oplock_break() leading to a use-after-free of the cinode structure when unmounting: cifs_oplock_break() _cifsFileInfo_put(cfile) cifsFileInfo_put_final() cifs_sb_deactive() [last ref, start releasing sb] kill_sb() kill_anon_super() generic_shutdown_super() evict_inodes() dispose_list() evict() destroy_inode() call_rcu(&inode->i_rcu, i_callback) spin_lock(&cinode->open_file_lock) <- OK [later] i_callback() cifs_free_inode() kmem_cache_free(cinode) spin_unlock(&cinode->open_file_lock) <- UAF cifs_done_oplock_break(cinode) <- UAF The issue occurs when umount has already released its reference to the superblock. When _cifsFileInfo_put() calls cifs_sb_deactive(), this releases the last reference, triggering the immediate cleanup of all inodes under RCU. However, cifs_oplock_break() continues to access the cinode after this point, resulting in use-after-free. Fix this by holding an extra reference to the superblock during the entire oplock break operation. This ensures that the superblock and its inodes remain valid until the oplock break completes.