bpftool: Fix memory leak in dump_xx_nlmsg on realloc failure

In function dump_xx_nlmsg(), when realloc() fails to allocate memory,
the original pointer to the buffer is overwritten with NULL. This causes
a memory leak because the previously allocated buffer becomes unreachable
without being freed.

Fixes: 7900efc19214 ("tools/bpf: bpftool: improve output format for bpftool net")
Signed-off-by: Yuan Chen <[email protected]>
Reviewed-by: Quentin Monnet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: chenyuan0001

src/net.c

@@ -366,17 +366,18 @@ static int dump_link_nlmsg(void *cookie, void *msg, struct nlattr **tb)
 {
 	struct bpf_netdev_t *netinfo = cookie;
 	struct ifinfomsg *ifinfo = msg;
+	struct ip_devname_ifindex *tmp;
 
 	if (netinfo->filter_idx > 0 && netinfo->filter_idx != ifinfo->ifi_index)
 		return 0;
 
 	if (netinfo->used_len == netinfo->array_len) {
-		netinfo->devices = realloc(netinfo->devices,
-			(netinfo->array_len + 16) *
-			sizeof(struct ip_devname_ifindex));
-		if (!netinfo->devices)
+		tmp = realloc(netinfo->devices,
+			(netinfo->array_len + 16) * sizeof(struct ip_devname_ifindex));
+		if (!tmp)
 			return -ENOMEM;
 
+		netinfo->devices = tmp;
 		netinfo->array_len += 16;
 	}
 	netinfo->devices[netinfo->used_len].ifindex = ifinfo->ifi_index;
@@ -395,6 +396,7 @@ static int dump_class_qdisc_nlmsg(void *cookie, void *msg, struct nlattr **tb)
 {
 	struct bpf_tcinfo_t *tcinfo = cookie;
 	struct tcmsg *info = msg;
+	struct tc_kind_handle *tmp;
 
 	if (tcinfo->is_qdisc) {
 		/* skip clsact qdisc */
@@ -406,11 +408,12 @@ static int dump_class_qdisc_nlmsg(void *cookie, void *msg, struct nlattr **tb)
 	}
 
 	if (tcinfo->used_len == tcinfo->array_len) {
-		tcinfo->handle_array = realloc(tcinfo->handle_array,
+		tmp = realloc(tcinfo->handle_array,
 			(tcinfo->array_len + 16) * sizeof(struct tc_kind_handle));
-		if (!tcinfo->handle_array)
+		if (!tmp)
 			return -ENOMEM;
 
+		tcinfo->handle_array = tmp;
 		tcinfo->array_len += 16;
 	}
 	tcinfo->handle_array[tcinfo->used_len].handle = info->tcm_handle;