[PATCH 7/8] nss: aiforaf: Decrease stack size by scoping off large buffers.

[Peter Krempa <pkrempa@xxxxxxxxxx>]

The 'buf', 'sa' and 'hints' stack allocated helper variables are never
used together. Decrease the stack memory usage by scoping them off into
do-while blocks.

In this instance we do not want to use dynamic allocation as this is the
NSS module.

Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx>
---
 tools/nss/libvirt_nss.c | 97 +++++++++++++++++++++++------------------
 1 file changed, 54 insertions(+), 43 deletions(-)

diff --git a/tools/nss/libvirt_nss.c b/tools/nss/libvirt_nss.c
index 37720bf4ae..dff3c034bf 100644
--- a/tools/nss/libvirt_nss.c
+++ b/tools/nss/libvirt_nss.c
@@ -470,61 +470,72 @@ aiforaf(const char *name,
         struct addrinfo **aip)
 {
     struct hostent resolved;
-    char buf[1024] = { 0 };
     int err;
-    int herr;
-    struct addrinfo hints;
-    struct addrinfo *res0;
-    struct addrinfo *res;
     char **addrList;

-    if (NSS_NAME(gethostbyname2)(name, af, &resolved,
-                                 buf, sizeof(buf),
-                                 &err, &herr) != NS_SUCCESS)
-        return;
+    /* Note: The do-while blocks in this function are used to scope off large
+     * stack allocated buffers, which are not needed at the same time */
+    do {
+        char buf[1024] = { 0 };
+        int herr;
+
+        if (NSS_NAME(gethostbyname2)(name, af, &resolved,
+                                     buf, sizeof(buf),
+                                     &err, &herr) != NS_SUCCESS)
+            return;
+    } while (false);

     addrList = resolved.h_addr_list;
     while (*addrList) {
-        union {
-            struct sockaddr sa;
-            struct sockaddr_in sin;
-            struct sockaddr_in6 sin6;
-        } sa = { 0 };
-        socklen_t salen;
         void *address = *addrList;
         char host[NI_MAXHOST];
+        struct addrinfo *res0;
+        struct addrinfo *res;
+
+        do  {
+            union {
+                struct sockaddr sa;
+                struct sockaddr_in sin;
+                struct sockaddr_in6 sin6;
+            } sa = { 0 };
+            socklen_t salen;
+
+            if (resolved.h_addrtype == AF_INET) {
+                sa.sin.sin_family = AF_INET;
+                memcpy(&sa.sin.sin_addr.s_addr,
+                       address,
+                       FAMILY_ADDRESS_SIZE(AF_INET));
+                salen = sizeof(sa.sin);
+            } else {
+                sa.sin6.sin6_family = AF_INET6;
+                memcpy(&sa.sin6.sin6_addr.s6_addr,
+                       address,
+                       FAMILY_ADDRESS_SIZE(AF_INET6));
+                salen = sizeof(sa.sin6);
+            }

-        if (resolved.h_addrtype == AF_INET) {
-            sa.sin.sin_family = AF_INET;
-            memcpy(&sa.sin.sin_addr.s_addr,
-                   address,
-                   FAMILY_ADDRESS_SIZE(AF_INET));
-            salen = sizeof(sa.sin);
-        } else {
-            sa.sin6.sin6_family = AF_INET6;
-            memcpy(&sa.sin6.sin6_addr.s6_addr,
-                   address,
-                   FAMILY_ADDRESS_SIZE(AF_INET6));
-            salen = sizeof(sa.sin6);
-        }
+            if ((err = getnameinfo(&sa.sa, salen,
+                                   host, sizeof(host),
+                                   NULL, 0,
+                                   NI_NUMERICHOST | NI_NUMERICSERV)) != 0) {
+                ERROR("Cannot convert socket address to string: %s",
+                      gai_strerror(err));
+                continue;
+            }
+        } while (false);

-        if ((err = getnameinfo(&sa.sa, salen,
-                               host, sizeof(host),
-                               NULL, 0,
-                               NI_NUMERICHOST | NI_NUMERICSERV)) != 0) {
-            ERROR("Cannot convert socket address to string: %s",
-                  gai_strerror(err));
-            continue;
-        }
+        do {
+            struct addrinfo hints;

-        hints = *pai;
-        hints.ai_flags = AI_NUMERICHOST;
-        hints.ai_family = af;
+            hints = *pai;
+            hints.ai_flags = AI_NUMERICHOST;
+            hints.ai_family = af;

-        if (getaddrinfo(host, NULL, &hints, &res0)) {
-            addrList++;
-            continue;
-        }
+            if (getaddrinfo(host, NULL, &hints, &res0)) {
+                addrList++;
+                continue;
+            }
+        } while (false);

         for (res = res0; res; res = res->ai_next)
             res->ai_flags = pai->ai_flags;
-- 
2.41.0