File arpwatch-2.1a11-drop-privs.dif of Package arpwatch
Index: arpwatch-3.1/arpwatch.c
===================================================================
--- arpwatch-3.1.orig/arpwatch.c
+++ arpwatch-3.1/arpwatch.c
@@ -71,6 +71,8 @@ struct rtentry;
#include <string.h>
#include <syslog.h>
#include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
#include <pcap.h>
@@ -170,6 +172,66 @@ int sanity_fddi(struct fddi_header *, st
int toskip(u_int32_t);
void usage(void) __attribute__((noreturn));
+void dropprivileges(const char* user)
+{
+ struct passwd* pw;
+ pw = getpwnam( user );
+ if ( pw ) {
+ char *arpfiledir;
+ char *lastslash;
+
+ arpfiledir = malloc(strlen(arpfile)+1);
+ if(arpfiledir == NULL) {
+ syslog(LOG_ERR, "Fatal: malloc().");
+ exit(1);
+ }
+ strcpy(arpfiledir, arpfile);
+ lastslash = strrchr(arpfiledir, '/');
+ if(lastslash == NULL) {
+ syslog(LOG_ERR, "Fatal: cannot determine directory of %s", arpfile);
+ exit(1);
+ }
+ lastslash[0]='\0';
+
+ if (!safe_base_path(arpfiledir)) {
+ syslog(LOG_ERR, "Fatal: directory structure %s not safe, can't operate here. Please make root owner of underlying directories and remove write access for other", arpfiledir);
+ exit(1);
+ }
+
+ // ensure we have a safe place to operate
+ if (lchown( arpfiledir, 0, 0) != 0 ) {
+ syslog(LOG_ERR, "Fatal: could not chown %s to root).", arpfiledir);
+ exit(1);
+ }
+ // change permissions of the file if it exists
+ if (!access(arpfile, F_OK) && lchown ( arpfile, pw->pw_uid, -1) != 0) {
+ syslog(LOG_ERR, "Fatal: could not chown %s to %d).", arpfile, pw->pw_uid);
+ exit(1);
+ }
+ /* files arp.dat.eth0- and arp.dat.eth0.new that are created
+ as backup/lastversion and for temporary storage are
+ deleted before created again, therefor the users needs
+ to control this directory . */
+ if ( lchown ( arpfiledir, pw->pw_uid, -1) != 0 ) {
+ syslog(LOG_ERR, "Fatal: could not chown %s to %d).",
+ arpfiledir, pw->pw_uid);
+ exit(1);
+ }
+ free(arpfiledir);
+ if ( initgroups(pw->pw_name, pw->pw_gid) != 0 || setgid(pw->pw_gid) != 0 ||
+ setuid(pw->pw_uid) != 0 ) {
+ syslog(LOG_ERR, "Fatal: Couldn't change to user/group '%.32s' uid=%d gid=%d", user,
+ pw->pw_uid, pw->pw_gid);
+ exit(1);
+ }
+ }
+ else {
+ syslog(LOG_ERR, "No such user: '%.32s'", user);
+ exit(1);
+ }
+ syslog(LOG_DEBUG, "arpwatch running as uid=%d gid=%d", getuid(), getgid());
+}
+
int
main(int argc, char **argv)
{
@@ -181,6 +243,7 @@ main(int argc, char **argv)
char *interface, *rfilename;
struct bpf_program code;
char errbuf[PCAP_ERRBUF_SIZE];
+ char *serveruser = NULL;
if (argv[0] == NULL)
prog = "arpwatch";
@@ -198,7 +261,7 @@ main(int argc, char **argv)
interface = NULL;
rfilename = NULL;
pd = NULL;
- while ((op = getopt(argc, argv, "CdD:Ff:i:n:NpP:qr:svw:W:x:zZ")) != EOF)
+ while ((op = getopt(argc, argv, "CdD:Ff:i:n:NpP:qr:svw:W:x:zZu:")) != EOF)
switch (op) {
case 'C':
@@ -283,6 +346,16 @@ main(int argc, char **argv)
zeropad = 1;
break;
+ case 'u':
+ if ( optarg ) {
+ serveruser = strdup(optarg);
+ }
+ else {
+ fprintf(stderr, "%s: Need username after -u\n", prog);
+ usage();
+ }
+ break;
+
default:
usage();
}
@@ -383,8 +456,9 @@ main(int argc, char **argv)
* Revert to non-privileged user after opening sockets
* (not needed on most systems).
*/
- setgid(getgid());
- setuid(getuid());
+ if ( serveruser ) {
+ dropprivileges( serveruser );
+ }
/* Must be ethernet or fddi */
linktype = pcap_datalink(pd);
@@ -933,6 +1007,6 @@ usage(void)
"usage: %s [-CdFNpqsvzZ] [-D arpdir] [-f datafile]"
" [-i interface]\n\t"
" [-P pidfile] [-w watcher@email] [-W watchee@email]\n\t"
- " [-n net[/width]] [-x net[/width]] [-r file]\n", prog);
+ " [-n net[/width]] [-x net[/width]] [-r file] [-u username]\n", prog);
exit(1);
}
Index: arpwatch-3.1/util.c
===================================================================
--- arpwatch-3.1.orig/util.c
+++ arpwatch-3.1/util.c
@@ -36,6 +36,7 @@ static const char rcsid[] =
#include <sys/types.h>
#include <sys/file.h>
+#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
@@ -212,3 +213,47 @@ savestr(const char *str)
strsize -= i;
return (cp);
}
+
+int safe_base_path(char *arpfiledir) {
+ // check directories below arpfiledir for safe ownwership/permissions
+ char *path_component;
+ char *lastslash = NULL;
+ int safe_path = 1;
+
+ if (!arpfiledir) {
+ syslog(LOG_ERR, "Fatal: safe_base_path invalid invocation.");
+ exit(1);
+ }
+
+ path_component = malloc(strlen(arpfiledir)+1);
+ if(path_component == NULL) {
+ syslog(LOG_ERR, "Fatal: malloc().");
+ exit(1);
+ }
+ strcpy(path_component, arpfiledir);
+
+ while ((lastslash = strrchr(path_component, '/'))) {
+ struct stat stats;
+
+ lastslash[0]='\0';
+ if ( lstat(path_component, &stats) ) {
+ /* on the last iteration the string will be empty and this fails,
+ which is okay, if / is unsafe all is lost anyway and we can
+ skip the check. Otherwise fail safe if lstat doesn't work */
+ if (strlen(path_component))
+ safe_path = 0;
+ } else {
+ if ( stats.st_uid != 0 ||
+ stats.st_gid != 0 ||
+ stats.st_mode & S_IWOTH
+ ) {
+ /* this is not a safe path to operate on with privileges because
+ it isn't owned by root:root or others can write there */
+ safe_path = 0;
+ }
+ }
+ }
+
+ free(path_component);
+ return safe_path;
+}
Index: arpwatch-3.1/util.h
===================================================================
--- arpwatch-3.1.orig/util.h
+++ arpwatch-3.1/util.h
@@ -8,6 +8,7 @@ char *intoa(u_int32_t);
void lg(int, const char *, ...) __attribute__ ((format (printf, 2, 3)));
int readdata(void);
char *savestr(const char *);
+int safe_base_path(char *);
extern char *arpdir;
extern char *arpfile;
