3 files changed, 26 insertions, 19 deletions

diff --git a/coreutils/test.c b/coreutils/test.c
index c02c92745..874285704 100644
--- a/coreutils/test.c
+++ b/coreutils/test.c
@@ -637,32 +637,14 @@ static int binop(void)
         /*return 1; - NOTREACHED */
 }
 
-static void initialize_group_array(void)
-{
-        group_array = bb_getgroups(&ngroups, NULL);
-}
-
 /* Return non-zero if GID is one that we have in our groups list. */
-//XXX: FIXME: duplicate of existing libbb function?
-// see toplevel TODO file:
-// possible code duplication ingroup() and is_a_group_member()
 static int is_a_group_member(gid_t gid)
 {
-        int i;
-
         /* Short-circuit if possible, maybe saving a call to getgroups(). */
         if (gid == getgid() || gid == getegid())
                 return 1;
 
-        if (ngroups == 0)
-                initialize_group_array();
-
-        /* Search through the list looking for GID. */
-        for (i = 0; i < ngroups; i++)
-                if (gid == group_array[i])
-                        return 1;
-
-        return 0;
+        return is_in_supplementary_groups(&ngroups, &group_array, gid);
 }
 
 /*
diff --git a/include/libbb.h b/include/libbb.h
index 67e7bf7b9..e06aef08e 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1201,6 +1201,11 @@ void die_if_bad_username(const char* name) FAST_FUNC;
  * Dies on errors (on Linux, only xrealloc can cause this, not internal getgroups call).
  */
 gid_t *bb_getgroups(int *ngroups, gid_t *group_array) FAST_FUNC;
+/*
+ * True if GID is in our getgroups() result.
+ * getgroups() is cached in group_array[], to makse successive calls faster.
+ */
+int FAST_FUNC is_in_supplementary_groups(int *pngroups, gid_t **pgroup_array, gid_t gid);
 
 #if ENABLE_FEATURE_UTMP
 void FAST_FUNC write_new_utmp(pid_t pid, int new_type, const char *tty_name, const char *username, const char *hostname);
diff --git a/libbb/bb_getgroups.c b/libbb/bb_getgroups.c
index 5d83c729a..f030d5eac 100644
--- a/libbb/bb_getgroups.c
+++ b/libbb/bb_getgroups.c
@@ -45,3 +45,23 @@ gid_t* FAST_FUNC bb_getgroups(int *ngroups, gid_t *group_array)
                 *ngroups = n;
         return group_array;
 }
+
+/* Return non-zero if GID is in our supplementary group list. */
+int FAST_FUNC is_in_supplementary_groups(int *pngroups, gid_t **pgroup_array, gid_t gid)
+{
+        int i;
+        int ngroups;
+        gid_t *group_array;
+
+        if (*pngroups == 0)
+                *pgroup_array = bb_getgroups(pngroups, NULL);
+        ngroups = *pngroups;
+        group_array = *pgroup_array;
+
+        /* Search through the list looking for GID. */
+        for (i = 0; i < ngroups; i++)
+                if (gid == group_array[i])
+                        return 1;
+
+        return 0;
+}