getgroups: don't expose GETGROUPS_T to user

These days, most systems already declare getgroups with gid_t*.
But in the rare case that GETGROUPS_T is still int but gid_t
is short, the user should not have to uglify their code; let
the replacement hide all the magic.

Tested by configuring with ac_cv_type_getgroups=uint64_t on a
platform with 32-bit gid_t, and ignoring compiler warnings.

However, since we don't replace setgroups, the GETGROUPS_T
workaround is still needed there for now.

* lib/getgroups.c (rpl_getgroups): Change signature.  Copy array
an element at a time if GETGROUPS_T is wrong size.
* lib/getugroups.h (getugroups): Change signature.
* lib/unistd.in.h (getgroups): Likewise.
* m4/getgroups.m4 (gl_FUNC_GETGROUPS): Use replacement if
signature needs fixing.
* m4/getugroups.m4 (gl_GETUGROUPS): No longer need
AC_TYPE_GETGROUPS.
* modules/group-member (Depends-on): Add getgroups.
* lib/group-member.c (group_info, get_group_info): Use gid_t.
(group_member): Rely on getgroups replacement.
* lib/getugroups.c (getugroups): Use gid_t.
* tests/test-getgroups.c (main): Likewise.
* NEWS: Mention the signature change.
* doc/posix-functions/getgroups.texi (getgroups): Mention the
problem with signature.
* doc/glibc-functions/setgroups.texi (setgroups): Mention that
GETGROUPS_T is still useful for setgroups.

Signed-off-by: Eric Blake <ebb9@byu.net>

1 files changed, 32 insertions, 2 deletions

diff --git a/lib/getgroups.c b/lib/getgroups.c
index bad676ea5e..e4540fe9b7 100644
--- a/lib/getgroups.c
+++ b/lib/getgroups.c
@@ -48,14 +48,44 @@ getgroups (int n _UNUSED_PARAMETER_, GETGROUPS_T *groups _UNUSED_PARAMETER_)
    whether the effective group id is included in the list.  */
 
 int
-rpl_getgroups (int n, GETGROUPS_T *group)
+rpl_getgroups (int n, gid_t *group)
 {
   int n_groups;
   GETGROUPS_T *gbuf;
   int saved_errno;
 
   if (n != 0)
-    return getgroups (n, group);
+    {
+      int result;
+      int saved_errno;
+      if (sizeof *group == sizeof *gbuf)
+        return getgroups (n, (GETGROUPS_T *) group);
+
+      if (n < 0)
+        {
+          errno = EINVAL;
+          return -1;
+        }
+      if (SIZE_MAX / sizeof *gbuf <= n)
+        {
+          errno = ENOMEM;
+          return -1;
+        }
+      gbuf = malloc (n * sizeof *gbuf);
+      if (!gbuf)
+        return -1;
+      result = getgroups (n, gbuf);
+      if (0 <= result)
+        {
+          n = result;
+          while (n--)
+            group[n] = gbuf[n];
+        }
+      saved_errno = errno;
+      free (gbuf);
+      errno == saved_errno;
+      return result;
+    }
 
   n = 20;
   while (1)