net/smc: check v2_ext_offset/eid_cnt/ism_gid_cnt when receiving proposal msg

When receiving proposal msg in server, the fields v2_ext_offset/
eid_cnt/ism_gid_cnt in proposal msg are from the remote client
and can not be fully trusted. Especially the field v2_ext_offset,
once exceed the max value, there has the chance to access wrong
address, and crash may happen.

This patch checks the fields v2_ext_offset/eid_cnt/ism_gid_cnt
before using them.

Fixes: 8c3dca341aea ("net/smc: build and send V2 CLC proposal")
Signed-off-by: Guangguan Wang <[e-mail]>
Reviewed-by: Wen Gu <[e-mail]>
Reviewed-by: D. Wythe <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/smc/af_smc.c

···
 		goto not_found;
 
 	smc_v2_ext = smc_get_clc_v2_ext(pclc);
-	if (!smc_clc_match_eid(ini->negotiated_eid, smc_v2_ext, NULL, NULL))
+	if (!smc_v2_ext ||
+	    !smc_clc_match_eid(ini->negotiated_eid, smc_v2_ext, NULL, NULL))
 		goto not_found;
 
 	/* prepare RDMA check */

net/smc/smc_clc.c

···
 	struct smc_clc_msg_hdr *hdr = &pclc->hdr;
 	struct smc_clc_v2_extension *v2_ext;
 
-	v2_ext = smc_get_clc_v2_ext(pclc);
 	pclc_prfx = smc_clc_proposal_get_prefix(pclc);
 	if (!pclc_prfx ||
 	    pclc_prfx->ipv6_prefixes_cnt > SMC_CLC_MAX_V6_PREFIX)
···
 			sizeof(struct smc_clc_msg_trail))
 			return false;
 	} else {
+		v2_ext = smc_get_clc_v2_ext(pclc);
+		if ((hdr->typev2 != SMC_TYPE_N &&
+		     (!v2_ext || v2_ext->hdr.eid_cnt > SMC_CLC_MAX_UEID)) ||
+		    (smcd_indicated(hdr->typev2) &&
+		     v2_ext->hdr.ism_gid_cnt > SMCD_CLC_MAX_V2_GID_ENTRIES))
+			return false;
+
 		if (ntohs(hdr->length) !=
 			sizeof(*pclc) +
 			sizeof(struct smc_clc_msg_smcd) +

net/smc/smc_clc.h

···
 smc_get_clc_v2_ext(struct smc_clc_msg_proposal *prop)
 {
 	struct smc_clc_msg_smcd *prop_smcd = smc_get_clc_msg_smcd(prop);
+	u16 max_offset;
 
-	if (!prop_smcd || !ntohs(prop_smcd->v2_ext_offset))
+	max_offset = offsetof(struct smc_clc_msg_proposal_area, pclc_v2_ext) -
+		     offsetof(struct smc_clc_msg_proposal_area, pclc_smcd) -
+		     offsetofend(struct smc_clc_msg_smcd, v2_ext_offset);
+
+	if (!prop_smcd || !ntohs(prop_smcd->v2_ext_offset) ||
+	    ntohs(prop_smcd->v2_ext_offset) > max_offset)
 		return NULL;
 
 	return (struct smc_clc_v2_extension *)