In preparation for raising NGROUPS and NGROUPS_MAX, change base

system callers of getgroups(), getgrouplist(), and setgroups() to
allocate buffers dynamically.  Specifically, allocate a buffer of size
sysconf(_SC_NGROUPS_MAX)+1 (+2 in a few cases to allow for overflow).

This (or similar gymnastics) is required for the code to actually follow
the POSIX.1-2008 specification where {NGROUPS_MAX} may differ at runtime
and where getgroups may return {NGROUPS_MAX}+1 results on systems like
FreeBSD which include the primary group.

In id(1), don't pointlessly add the primary group to the list of all
groups, it is always the first result from getgroups().  In principle
the old code was more portable, but this was only done in one of the two
places where getgroups() was called to the overall effect was pointless.

Document the actual POSIX requirements in the getgroups(2) and
setgroups(2) manpages.  We do not yet support a dynamic NGROUPS, but we
may in the future.

MFC after:	2 weeks

5 files changed, 42 insertions, 20 deletions

diff --git a/lib/libc/gen/initgroups.3 b/lib/libc/gen/initgroups.3
index 2fe2dd9..3ed3ca7 100644
--- a/lib/libc/gen/initgroups.3
+++ b/lib/libc/gen/initgroups.3
@@ -65,6 +65,13 @@ function may fail and set
 .Va errno
 for any of the errors specified for the library function
 .Xr setgroups 2 .
+It may also return:
+.Bl -tag -width Er
+.It Bq Er ENOMEM
+The
+.Fn initgroups
+function was unable to allocate temporary storage.
+.El
 .Sh SEE ALSO
 .Xr setgroups 2 ,
 .Xr getgrouplist 3
diff --git a/lib/libc/gen/initgroups.c b/lib/libc/gen/initgroups.c
index 299ae50..aacaf7e 100644
--- a/lib/libc/gen/initgroups.c
+++ b/lib/libc/gen/initgroups.c
@@ -35,10 +35,12 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 
-#include <stdio.h>
 #include "namespace.h"
 #include <err.h>
 #include "un-namespace.h"
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <unistd.h>
 
 int
@@ -46,14 +48,21 @@ initgroups(uname, agroup)
 	const char *uname;
 	gid_t agroup;
 {
-	int ngroups;
+	int ngroups, ret;
+	long ngroups_max;
+	gid_t *groups;
+
 	/*
-	 * Provide space for one group more than NGROUPS to allow
+	 * Provide space for one group more than possible to allow
 	 * setgroups to fail and set errno.
 	 */
-	gid_t groups[NGROUPS + 1];
+	ngroups_max = sysconf(_SC_NGROUPS_MAX) + 2;
+	if ((groups = malloc(sizeof(*groups) * ngroups_max)) == NULL)
+		return (ENOMEM);
 
-	ngroups = NGROUPS + 1;
+	ngroups = (int)ngroups_max;
 	getgrouplist(uname, agroup, groups, &ngroups);
-	return (setgroups(ngroups, groups));
+	ret = setgroups(ngroups, groups);
+	free(groups);
+	return (ret);
 }
diff --git a/lib/libc/rpc/auth_unix.c b/lib/libc/rpc/auth_unix.c
index 5801015..ff3ca7b 100644
--- a/lib/libc/rpc/auth_unix.c
+++ b/lib/libc/rpc/auth_unix.c
@@ -185,23 +185,29 @@ authunix_create(machname, uid, gid, len, aup_gids)
 AUTH *
 authunix_create_default()
 {
-	int len;
+	int ngids;
+	long ngids_max;
 	char machname[MAXHOSTNAMELEN + 1];
 	uid_t uid;
 	gid_t gid;
-	gid_t gids[NGROUPS_MAX];
+	gid_t *gids;
+
+	ngids_max = sysconf(_SC_NGROUPS_MAX) + 1;
+	gids = malloc(sizeof(gid_t) * ngids_max);
+	if (gids == NULL)
+		return (NULL);
 
 	if (gethostname(machname, sizeof machname) == -1)
 		abort();
 	machname[sizeof(machname) - 1] = 0;
 	uid = geteuid();
 	gid = getegid();
-	if ((len = getgroups(NGROUPS_MAX, gids)) < 0)
+	if ((ngids = getgroups(ngids_max, gids)) < 0)
 		abort();
-	if (len > NGRPS)
-		len = NGRPS;
+	if (ngids > NGRPS)
+		ngids = NGRPS;
 	/* XXX: interface problem; those should all have been unsigned */
-	return (authunix_create(machname, (int)uid, (int)gid, len,
+	return (authunix_create(machname, (int)uid, (int)gid, ngids,
 	    (int *)gids));
 }
 
diff --git a/lib/libc/sys/getgroups.2 b/lib/libc/sys/getgroups.2
index 5eadfe1..4fd8fee 100644
--- a/lib/libc/sys/getgroups.2
+++ b/lib/libc/sys/getgroups.2
@@ -58,10 +58,7 @@ The
 system call
 returns the actual number of groups returned in
 .Fa gidset .
-No more than
-.Dv NGROUPS_MAX
-will ever
-be returned.
+At least one and as many as {NGROUPS_MAX}+1 values may be returned.
 If
 .Fa gidsetlen
 is zero,
@@ -92,6 +89,11 @@ an invalid address.
 .Sh SEE ALSO
 .Xr setgroups 2 ,
 .Xr initgroups 3
+.Sh STANDARDS
+The
+.Fn getgroups
+system call conforms to
+.St -p1003.1-2008 .
 .Sh HISTORY
 The
 .Fn getgroups
diff --git a/lib/libc/sys/setgroups.2 b/lib/libc/sys/setgroups.2
index e56e95f..ef4c34c 100644
--- a/lib/libc/sys/setgroups.2
+++ b/lib/libc/sys/setgroups.2
@@ -53,9 +53,7 @@ The
 argument
 indicates the number of entries in the array and must be no
 more than
-.Dv NGROUPS ,
-as defined in
-.In sys/param.h .
+.Dv {NGROUPS_MAX}+1 .
 .Pp
 Only the super-user may set a new group list.
 .Sh RETURN VALUES
@@ -71,7 +69,7 @@ The caller is not the super-user.
 The number specified in the
 .Fa ngroups
 argument is larger than the
-.Dv NGROUPS
+.Dv {NGROUPS_MAX}+1
 limit.
 .It Bq Er EFAULT
 The address specified for