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small correctness fixes for nscd
From: |
Christopher Allen Wing |
Subject: |
small correctness fixes for nscd |
Date: |
Fri, 4 Jan 2002 11:25:31 -0500 (EST) |
Hello,
there are a few bugs in the nscd code for running nscd as a user other
than root:
- there is no error checking for setuid(), setgid(), and setgroups().
(bad)
- nscd does setgroups(0, NULL) instead of actually looking up the groups
of which 'server_user' is a member.
- if nscd is configured to run as an unprivileged user and is also run in
'secure mode', it silently ignores the configuration file and runs as
root anyway.
- in drop_privileges(), nscd duplicates some internal code for looking up
a passwd entry, instead of using the normal functions.
Here is a patch to fix these problems.
Thanks,
Chris Wing
address@hidden
The patch can be downloaded from:
http://www.engin.umich.edu/caen/systems/Linux/code/patches/glibc-2.2.4-nscd.patch
or just grab it from below.
--- glibc-2.2.4/nscd/Makefile.orig Mon Jul 9 14:57:42 2001
+++ glibc-2.2.4/nscd/Makefile Wed Jan 2 20:11:34 2002
@@ -25,9 +25,12 @@
include ../Makeconfig
+# To find xmalloc.c
+vpath %.c ../locale/programs
+
nscd-modules := nscd connections pwdcache getpwnam_r getpwuid_r grpcache \
getgrnam_r getgrgid_r hstcache gethstbyad_r gethstbynm2_r \
- dbg_log nscd_conf nscd_stat cache
+ dbg_log nscd_conf nscd_stat cache xmalloc
ifeq ($(have-thread-library),yes)
--- glibc-2.2.4/nscd/connections.c.orig Wed Jul 18 13:51:59 2001
+++ glibc-2.2.4/nscd/connections.c Fri Jan 4 11:05:11 2002
@@ -21,7 +21,10 @@
#include <assert.h>
#include <error.h>
#include <errno.h>
+#include <grp.h>
#include <pthread.h>
+#include <pwd.h>
+#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <libintl.h>
@@ -35,6 +38,24 @@
#include "nscd.h"
#include "dbg_log.h"
+/* Wrapper functions with error checking for standard functions. */
+extern void *xmalloc (size_t n);
+extern void *xcalloc (size_t n, size_t s);
+extern void *xrealloc (void *o, size_t n);
+
+/* Support to run nscd as an unprivileged user */
+const char *server_user = NULL;
+uid_t server_uid;
+gid_t server_gid;
+gid_t *server_groups;
+#ifndef NGROUPS
+#define NGROUPS 32
+#endif
+int server_ngroups = NGROUPS;
+
+static void begin_drop_privileges (void);
+static void finish_drop_privileges (void);
+
/* Mapping of request type to database. */
static const dbtype serv2db[LASTDBREQ + 1] =
@@ -125,6 +146,19 @@
dbg_log (_("cannot read configuration file; this is fatal"));
exit (1);
}
+
+ /* Secure mode and unprivileged mode are incompatible */
+ if (server_user && secure_in_use)
+ {
+ dbg_log (_("Cannot run nscd in secure mode as unprivileged user"));
+ exit (1);
+ }
+
+ /* Look up unprivileged uid/gid/groups before we start listening on the
+ socket */
+ if (server_user)
+ begin_drop_privileges ();
+
if (nthreads == -1)
/* No configuration for this value, assume a default. */
nthreads = 2 * lastdb;
@@ -184,6 +218,10 @@
strerror (errno));
exit (1);
}
+
+ /* Change to unprivileged uid/gid/groups if specifed in config file */
+ if (server_user)
+ finish_drop_privileges ();
}
@@ -549,3 +587,70 @@
/* Prune the host database */
prune_cache (&dbs[hstdb], LONG_MAX);
}
+
+
+/* Look up the uid, gid, and supplementary groups to run nscd as. When
+ this function is called, we are not listening on the nscd socket yet so
+ we can just use the ordinary lookup functions without causing a lockup */
+static void
+begin_drop_privileges (void)
+{
+ struct passwd *pwd;
+
+ pwd = getpwnam (server_user);
+
+ if (!pwd)
+ {
+ dbg_log (_("Failed to run nscd as user '%s'"), server_user);
+
+ /* XXX if the user does not exist, the error code given is ENOENT,
+ which might be a little confusing to people */
+ perror ("getpwnam");
+ exit (1);
+ }
+
+ server_uid = pwd->pw_uid;
+ server_gid = pwd->pw_gid;
+
+ server_groups = (gid_t *) xmalloc (server_ngroups * sizeof (gid_t));
+
+ if (!getgrouplist (server_user, server_gid, server_groups, &server_ngroups))
+ return;
+
+ server_groups = xrealloc (server_groups, server_ngroups * sizeof (gid_t));
+
+ if (getgrouplist (server_user, server_gid, server_groups, &server_ngroups)
== -1)
+ {
+ dbg_log (_("Failed to run nscd as user '%s'"), server_user);
+ perror ("getgrouplist");
+ exit (1);
+ }
+}
+
+
+/* Call setgroups(), setgid(), and setuid() to drop root privileges and
+ run nscd as the user specified in the configuration file. */
+static void
+finish_drop_privileges (void)
+{
+ if (setgroups (server_ngroups, server_groups) == -1)
+ {
+ dbg_log (_("Failed to run nscd as user '%s'"), server_user);
+ perror ("setgroups");
+ exit (1);
+ }
+
+ if (setgid (server_gid) == -1)
+ {
+ dbg_log (_("Failed to run nscd as user '%s'"), server_user);
+ perror ("setgid");
+ exit (1);
+ }
+
+ if (setuid (server_uid) == -1)
+ {
+ dbg_log (_("Failed to run nscd as user '%s'"), server_user);
+ perror ("setuid");
+ exit (1);
+ }
+}
--- glibc-2.2.4/nscd/nscd.c.orig Mon Jul 9 15:42:54 2001
+++ glibc-2.2.4/nscd/nscd.c Thu Jan 3 16:18:36 2002
@@ -23,11 +23,9 @@
#include <assert.h>
#include <errno.h>
#include <error.h>
-#include <grp.h>
#include <libintl.h>
#include <locale.h>
#include <pthread.h>
-#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
@@ -63,7 +61,6 @@
int disabled_passwd;
int disabled_group;
int go_background = 1;
-const char *server_user;
int secure[lastdb];
int secure_in_use;
@@ -71,7 +68,6 @@
static int check_pid (const char *file);
static int write_pid (const char *file);
-static void drop_privileges (void);
/* Name and version of program. */
static void print_version (FILE *stream, struct argp_state *state);
@@ -173,10 +169,6 @@
/* Init databases. */
nscd_init (conffile);
- /* Change to unprivileged UID if specifed in config file */
- if(server_user && !secure_in_use)
- drop_privileges ();
-
/* Handle incoming requests */
start_threads ();
@@ -377,36 +369,3 @@
return 0;
}
-
-/* Look up the uid and gid associated with the user we are supposed to run
- the server as, and then call setgid(), setgroups(), and setuid().
- Otherwise, abort- we should not run as root if the configuration file
- specifically tells us not to. */
-
-static void
-drop_privileges (void)
-{
- int buflen = 256;
- char *buffer = alloca (buflen);
- struct passwd resultbuf;
- struct passwd *pwd;
-
- while (__getpwnam_r (server_user, &resultbuf, buffer, buflen, &pwd) != 0
- && errno == ERANGE)
- {
- errno = 0;
- buflen += 256;
- buffer = alloca (buflen);
- }
-
- if(!pwd)
- {
- dbg_log (_("Failed to look up user '%s' to run server as"),
- server_user);
- exit(1);
- }
-
- setgroups (0, NULL);
- setgid (pwd->pw_gid);
- setuid (pwd->pw_uid);
-}
- small correctness fixes for nscd,
Christopher Allen Wing <=