add alternate backend support for getgrouplist

This completes the alternate backend support that was previously added
to the getpw* and getgr* functions. Unlike those, though, it
unconditionally queries nscd. Any groups from nscd that aren't in the
/etc/groups file are added to the returned list, and any that are
present in the file are ignored. The purpose of this behavior is to
provide a view of the group database consistent with what is observed
by the getgr* functions. If group memberships reported by nscd were
honored when the corresponding group already has a definition in the
/etc/groups file, the user's getgrouplist-based membership in the
group would conflict with their non-membership in the reported
gr_mem[] for the group.

The changes made also make getgrouplist thread-safe and eliminate its
clobbering of the global getgrent state.

src/misc/getgrouplist.c

@@ -1,24 +0,0 @@
-#define _GNU_SOURCE
-#include <grp.h>
-#include <string.h>
-#include <limits.h>
-
-int getgrouplist(const char *user, gid_t gid, gid_t *groups, int *ngroups)
-{
-	size_t n, i;
-	struct group *gr;
-	if (*ngroups<1) return -1;
-	n = *ngroups;
-	*groups++ = gid;
-	*ngroups = 1;
-
-	setgrent();
-	while ((gr = getgrent()) && *ngroups < INT_MAX) {
-		for (i=0; gr->gr_mem[i] && strcmp(user, gr->gr_mem[i]); i++);
-		if (!gr->gr_mem[i]) continue;
-		if (++*ngroups <= n) *groups++ = gr->gr_gid;
-	}
-	endgrent();
-
-	return *ngroups > n ? -1 : *ngroups;
-}

src/passwd/getgrouplist.c

@@ -0,0 +1,80 @@
+#define _GNU_SOURCE
+#include "pwf.h"
+#include <grp.h>
+#include <string.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <byteswap.h>
+#include <errno.h>
+#include "nscd.h"
+
+int getgrouplist(const char *user, gid_t gid, gid_t *groups, int *ngroups)
+{
+	int rv, nlim, ret = -1;
+	ssize_t i, n = 1;
+	struct group gr;
+	struct group *res;
+	FILE *f;
+	int swap = 0;
+	int32_t resp[INITGR_LEN];
+	uint32_t *nscdbuf = 0;
+	char *buf = 0;
+	char **mem = 0;
+	size_t nmem = 0;
+	size_t size;
+	nlim = *ngroups;
+	if (nlim >= 1) *groups++ = gid;
+
+	f = __nscd_query(GETINITGR, user, resp, sizeof resp, &swap);
+	if (!f) goto cleanup;
+	if (f != (FILE*)-1 && resp[INITGRFOUND]) {
+		nscdbuf = calloc(resp[INITGRNGRPS], sizeof(uint32_t));
+		if (!nscdbuf) goto cleanup;
+		if (!fread(nscdbuf, sizeof(*nscdbuf)*resp[INITGRNGRPS], 1, f)) {
+			if (!ferror(f)) errno = EIO;
+			goto cleanup;
+		}
+		if (swap) {
+			for (i = 0; i < resp[INITGRNGRPS]; i++)
+				nscdbuf[i] = bswap_32(nscdbuf[i]);
+		}
+	}
+	if (f != (FILE*)-1) fclose(f);
+
+	f = fopen("/etc/group", "rbe");
+	if (!f && errno != ENOENT && errno != ENOTDIR)
+		goto cleanup;
+
+	if (f) {
+		while (!(rv = __getgrent_a(f, &gr, &buf, &size, &mem, &nmem, &res)) && res) {
+			if (nscdbuf)
+				for (i=0; i < resp[INITGRNGRPS]; i++) {
+					if (nscdbuf[i] == gr.gr_gid) nscdbuf[i] = gid;
+				}
+			for (i=0; gr.gr_mem[i] && strcmp(user, gr.gr_mem[i]); i++);
+			if (!gr.gr_mem[i]) continue;
+			if (++n <= nlim) *groups++ = gr.gr_gid;
+		}
+		if (rv) {
+			errno = rv;
+			goto cleanup;
+		}
+	}
+	if (nscdbuf) {
+		for(i=0; i < resp[INITGRNGRPS]; i++) {
+			if (nscdbuf[i] != gid)
+				if(++n <= nlim) *groups++ = nscdbuf[i];
+		}
+	}
+
+	ret = n > nlim ? -1 : n;
+	*ngroups = n;
+
+cleanup:
+	if (f) fclose(f);
+	free(nscdbuf);
+	free(buf);
+	free(mem);
+	return ret;
+}

src/passwd/nscd.h

@@ -8,6 +8,7 @@
 #define GETPWBYUID 1
 #define GETGRBYNAME 2
 #define GETGRBYGID 3
+#define GETINITGR 15
 
 #define REQVERSION 0
 #define REQTYPE 1
@@ -33,6 +34,11 @@
 #define GRMEMCNT 5
 #define GR_LEN 6
 
+#define INITGRVERSION 0
+#define INITGRFOUND 1
+#define INITGRNGRPS 2
+#define INITGR_LEN 3
+
 FILE *__nscd_query(int32_t req, const char *key, int32_t *buf, size_t len, int *swap);
 
 #endif