CVE-2026-89641

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

cifs: clear tcon after cifsFileInfo_put() in cifs_file_set_size()

When the else branch of cifs_file_set_size() finds a writable file handle

via find_writable_file(), it borrows tcon and server from the handle's

tlink, attempts the handle-based set_file_size() RPC, and then releases

the handle with cifsFileInfo_put().

If set_file_size() fails, execution falls through to the path-based

fallback, which reuses the borrowed tcon and server under the

"if (tcon == NULL)" guard. Since tcon is not NULL at that point, the

guard is skipped. If cifsFileInfo_put() dropped the last reference on a

tlink that was already removed from the tlink tree (TCON_LINK_IN_TREE

cleared, as happens during reconnection or session teardown),

cifs_put_tlink() will have freed tcon; the subsequent set_path_size()

call is then a use-after-free.

Setting tcon = NULL after cifsFileInfo_put() causes the existing guard

to take the cifs_sb_tlink() path

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References