6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aswin Karuvally commit b264d8422779d69febce914efc47a92a85cc382c upstream. 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. Fixes: 293d984f0e36 ("ctcm: infrastructure for replaced ctc driver") Cc: stable@vger.kernel.org Signed-off-by: Aswin Karuvally Link: https://patch.msgid.link/20260827063408.2168914-1-aswin@linux.ibm.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- drivers/s390/net/ctcm_mpc.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/drivers/s390/net/ctcm_mpc.c +++ b/drivers/s390/net/ctcm_mpc.c @@ -827,7 +827,7 @@ static void mpc_action_go_ready(fsm_inst fsm_deltimer(&grp->timer); - if (grp->saved_xid2->xid2_flag2 == 0x40) { + if (priv->xid->xid2_flag2 == 0x40) { priv->xid->xid2_flag2 = 0x00; if (grp->estconnfunc) { grp->estconnfunc(grp->port_num, 1, @@ -1637,7 +1637,6 @@ done: "The XID used in the MPC protocol is not valid, " "rc = %d\n", rc); priv->xid->xid2_flag2 = 0x40; - grp->saved_xid2->xid2_flag2 = 0x40; } return rc;