lib: Avoid a malloc/realloc in getgroups_unix_user

This avoids a malloc/free in the most common case of a user with just a few
group memberships

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

diff --git a/source3/lib/system_smbd.c b/source3/lib/system_smbd.c
index 54381628c756c83b21491457ad5fbffcff9a3b36..3b1ac9c1c2a986d7c04bef53f20fb0d74f73953e 100644 (file)
--- a/source3/lib/system_smbd.c
+++ b/source3/lib/system_smbd.c
@@ -205,29 +205,26 @@ bool getgroups_unix_user(TALLOC_CTX *mem_ctx, const char *user,
                         gid_t primary_gid,
                         gid_t **ret_groups, uint32_t *p_ngroups)
 {
+       int max_grp = MIN(128, groups_max());
+       gid_t stack_groups[max_grp];
        uint32_t ngrp;
-       int max_grp;
-       gid_t *temp_groups;
+       gid_t *temp_groups = stack_groups;
+       gid_t *to_free = NULL;
        gid_t *groups;
        int i;
 
-       max_grp = MIN(128, groups_max());
-       temp_groups = SMB_MALLOC_ARRAY(gid_t, max_grp);
-       if (! temp_groups) {
-               return False;
-       }
-
        if (sys_getgrouplist(user, primary_gid, temp_groups, &max_grp) == -1) {
-               temp_groups = SMB_REALLOC_ARRAY(temp_groups, gid_t, max_grp);
-               if (!temp_groups) {
+               to_free = talloc_array(mem_ctx, gid_t, max_grp);
+               if (!to_free) {
                        return False;
                }
+               temp_groups = to_free;
 
                if (sys_getgrouplist(user, primary_gid,
                                     temp_groups, &max_grp) == -1) {
                        DEBUG(0, ("get_user_groups: failed to get the unix "
                                  "group list\n"));
-                       SAFE_FREE(temp_groups);
+                       TALLOC_FREE(to_free);
                        return False;
                }
        }
@@ -237,20 +234,20 @@ bool getgroups_unix_user(TALLOC_CTX *mem_ctx, const char *user,
 
        /* Add in primary group first */
        if (!add_gid_to_array_unique(mem_ctx, primary_gid, &groups, &ngrp)) {
-               SAFE_FREE(temp_groups);
+               TALLOC_FREE(to_free);
                return False;
        }
 
        for (i=0; i<max_grp; i++) {
                if (!add_gid_to_array_unique(mem_ctx, temp_groups[i],
                                        &groups, &ngrp)) {
-                       SAFE_FREE(temp_groups);
+                       TALLOC_FREE(to_free);
                        return False;
                }
        }
 
        *p_ngroups = ngrp;
        *ret_groups = groups;
-       SAFE_FREE(temp_groups);
+       TALLOC_FREE(to_free);
        return True;
 }