CVE-2026-99126

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

s390/ctcm: Prevent XID null dereference

The mpc validate xid() function sets grp->saved xid2->xid2 flag2 to 0x40 to signal XID validation error. If peer XID is NULL or r/w channel pairing mismatch happens, grp->saved xid2 is never initialized. An attempt to set the flag in such case leads to NULL dereference.

Fix this by using the always available priv->xid->xid2 flag2 instead of grp->saved xid2->xid2 flag2 for validation errors.