CVE-2026-89631

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

smb: client: reject a tree connect response whose byte count is too small

CIFSTCon() bounds its strnlen() over the byte area with the server's ByteCount minus two, which for ByteCount 0 or 1 goes negative as an int and converts to a huge size t. The later subtraction wraps the u16 bytes left, and that is what bounds cifs strndup from utf16(): a bound of up to 65535 against a ~16 KB cifs req poolp object runs off the end of the slab object, and the bytes reach userspace through tcon->nativeFileSystem in /proc/fs/cifs/DebugData.

Reject a byte area too small for what the parser consumes. Two bytes is the least it can consume, and no conformant response carries fewer. The new trace point is the 129th smb eio trace entry, which mode(byte) cannot represent, so the attribute goes with it.