CVE-2025-38527

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.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/09bce2138a30ef10d8821c8c3f73a4ab7a5726bc
• https://git.kernel.org/stable/c/0a4eec84d4d2c4085d4ed8630fd74e4b39033c1b
• https://git.kernel.org/stable/c/2baaf5bbab2ac474c4f92c10fcb3310f824db995
• https://git.kernel.org/stable/c/4256a483fe58af66a46cbf3dc48ff26e580d3308
• https://git.kernel.org/stable/c/705c79101ccf9edea5a00d761491a03ced314210
• https://git.kernel.org/stable/c/da11bd4b697b393a207f19a2ed7d382a811a3ddc
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html