From: Stanislav Brabec <sbrabec@suse.cz>
Date: Tue, 7 Oct 2025 23:14:32 +0000 (+0200)
Subject: netaddrq: Fix crash if there are no IP addresses
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=60c5c0516e6ce52863b12343a1cd276423ab3bae;p=thirdparty%2Futil-linux.git

netaddrq: Fix crash if there are no IP addresses

If there are no IP addresses, ul_netaddrq_bestaddr() returns threshold
ULNETLINK_RATING_BAD, but there were no addresses in the best array, and
best_ifaceq remains unset, which caused crash. Setting the initial
threshold to __ULNETLINK_RATING_MAX and checking for that value fixes that.
And more, it also allows to accept IP addresses with ULNETLINK_RATING_BAD
rating.

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
---

diff --git a/include/netaddrq.h b/include/netaddrq.h
index 6d5e655f5..d9c595f32 100644
--- a/include/netaddrq.h
+++ b/include/netaddrq.h
@@ -94,8 +94,11 @@ ul_netaddrq_iface_bestaddr(struct list_head *ipq_list,
  *   best_iface: interface where the best address was seen
  *   best array: best ifa_valid lifetime seen per quality rating
  *   return value: best rating seen
- * Note: It can be needed to call it twice: once for ip_quality_list_4, once
- * for ip_quality_list_6.
+ * Notes:
+ * - It can be needed to call it twice: once for ip_quality_list_4, once
+ *   for ip_quality_list_6.
+ * - If no IP addresses are found, the function can return
+ *   _ULNETLINK_RATING_MAX!
  */
 enum ul_netaddrq_ip_rating
 ul_netaddrq_bestaddr(struct ul_nl_data *nl,
@@ -109,8 +112,11 @@ ul_netaddrq_bestaddr(struct ul_nl_data *nl,
  *   return value: The best address as a string
  *   threshold: The best rating ever seen.
  *   best_ifaceq: The best rated interfece ever seen.
- * Note: It can be needed to call it twice: once for AF_INET, once
- * for AF_INET6.
+ * Notes:
+ * - It can be needed to call it twice: once for AF_INET, once
+ *   for AF_INET6.
+ * - If the return value is NULL (i. e. there are no usable interfaces), then
+ *   *best_ifaceq remains unchanges and cannot be used.
  */
 const char *ul_netaddrq_get_best_ipp(struct ul_nl_data *nl,
 				     uint8_t ifa_family,
diff --git a/lib/netaddrq.c b/lib/netaddrq.c
index 34431d8d3..1ce454aaf 100644
--- a/lib/netaddrq.c
+++ b/lib/netaddrq.c
@@ -296,7 +296,7 @@ ul_netaddrq_iface_bestaddr(struct list_head *ipq_list,
 	struct ul_netaddrq_ip *ipq;
 	enum ul_netaddrq_ip_rating threshold;
 
-	threshold = ULNETLINK_RATING_BAD;
+	threshold = __ULNETLINK_RATING_MAX;
 	list_for_each(li, ipq_list)
 	{
 		ipq = list_entry(li, struct ul_netaddrq_ip, entry);
@@ -342,7 +342,7 @@ ul_netaddrq_bestaddr(struct ul_nl_data *nl,
 		ipqo = offsetof(struct ul_netaddrq_iface, ip_quality_list_6);
 	}
 
-	threshold = ULNETLINK_RATING_BAD;
+	threshold = __ULNETLINK_RATING_MAX;
 	list_for_each(li, &(addrq->ifaces))
 	{
 		struct list_head *ipq_list;
@@ -374,7 +374,7 @@ const char *ul_netaddrq_get_best_ipp(struct ul_nl_data *nl,
 
 	memset(best, 0, sizeof(best));
 	*threshold = ul_netaddrq_bestaddr(nl, best_ifaceq, &best, ifa_family);
-	if (best[*threshold])
+	if (*threshold != __ULNETLINK_RATING_MAX)
 		return ul_nl_addr_ntop_address(best[*threshold]->addr);
 	return NULL;
 }
@@ -423,7 +423,7 @@ static void dump_iface_best(struct ul_nl_data *nl,
 	memset(best, 0, sizeof(best));
 	threshold = ul_netaddrq_iface_bestaddr(&(ifaceq->ip_quality_list_4),
 					       &best);
-	if (best[threshold])
+	if (threshold != __ULNETLINK_RATING_MAX)
 	{
 		fprintf(netout, "%s IPv4: %s", (first ? "best address" : " "),
 		       ul_nl_addr_ntop_address(best[threshold]->addr));
@@ -432,7 +432,7 @@ static void dump_iface_best(struct ul_nl_data *nl,
 	memset(best, 0, sizeof(best));
 	threshold = ul_netaddrq_iface_bestaddr(&(ifaceq->ip_quality_list_6),
 					       &best);
-	if (best[threshold])
+	if (threshold != __ULNETLINK_RATING_MAX)
 	{
 		fprintf(netout, "%s IPv6: %s", (first ? "best address" : " "),
 		       ul_nl_addr_ntop_address(best[threshold]->addr));
diff --git a/term-utils/agetty.c b/term-utils/agetty.c
index b7786ce7d..ec922bd11 100644
--- a/term-utils/agetty.c
+++ b/term-utils/agetty.c
@@ -2603,7 +2603,7 @@ static void print_iface_best(struct issue *ie,
 
 		threshold =
 			ul_netaddrq_iface_bestaddr(l, &best);
-		if (best[threshold])
+		if (threshold != __ULNETLINK_RATING_MAX)
 			fputs(ul_nl_addr_ntop_address(best[threshold]->addr),
 			      ie->output);
 	}