CVE-2026-99126: s390/ctcm: Prevent XID null dereference
In the Linux kernel, the following vulnerability has been resolved:
s390/ctcm: Prevent XID null dereference
The mpcvalidatexid() function sets grp->savedxid2->xid2flag2 to 0x40 to signal XID validation error. If peer XID is NULL or r/w channel pairing mismatch happens, grp->savedxid2 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->xid2flag2 instead of grp->savedxid2->xid2flag2 for validation errors.
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
In s390/ctcm mpc_validate_xid(), use the always-available priv->xid->xid2_flag2 instead of grp->saved_xid2->xid2_flag2 to signal XID validation errors, preventing NULL dereference when grp->saved_xid2 is uninitialized.