svn commit: r306761 - head/usr.bin/write
Conrad E. Meyer
cem at FreeBSD.org
Thu Oct 6 14:55:17 UTC 2016
Author: cem
Date: Thu Oct 6 14:55:15 2016
New Revision: 306761
URL: https://svnweb.freebsd.org/changeset/base/306761
Log:
write(1): Capsicumify
Enter Capsicum capability sandbox pretty early in this setuid program.
Some minor modifications were needed to cache directory fds and use
relative lookups.
Rights restriction of the stdio descriptors is unfortunately pretty messy
because we need an ioctl capability not present in the current libcapsicum
helpers (FIODGNAME).
Reviewed by: ed
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D7999
Modified:
head/usr.bin/write/write.c
Modified: head/usr.bin/write/write.c
==============================================================================
--- head/usr.bin/write/write.c Thu Oct 6 14:42:06 2016 (r306760)
+++ head/usr.bin/write/write.c Thu Oct 6 14:55:15 2016 (r306761)
@@ -46,12 +46,16 @@ static char sccsid[] = "@(#)write.c 8.1
__FBSDID("$FreeBSD$");
#include <sys/param.h>
+#include <sys/capsicum.h>
+#include <sys/filio.h>
#include <sys/signal.h>
#include <sys/stat.h>
-#include <sys/file.h>
#include <sys/time.h>
+
+#include <capsicum_helpers.h>
#include <ctype.h>
#include <err.h>
+#include <errno.h>
#include <locale.h>
#include <paths.h>
#include <pwd.h>
@@ -64,23 +68,76 @@ __FBSDID("$FreeBSD$");
#include <wctype.h>
void done(int);
-void do_write(char *, char *, uid_t);
+void do_write(int, char *, char *, const char *);
static void usage(void);
-int term_chk(char *, int *, time_t *, int);
+int term_chk(int, char *, int *, time_t *, int);
void wr_fputs(wchar_t *s);
-void search_utmp(char *, char *, char *, uid_t);
+void search_utmp(int, char *, char *, char *, uid_t);
int utmp_chk(char *, char *);
int
main(int argc, char **argv)
{
+ unsigned long cmds[] = { TIOCGETA, TIOCGWINSZ, FIODGNAME };
+ cap_rights_t rights;
+ struct passwd *pwd;
time_t atime;
uid_t myuid;
int msgsok, myttyfd;
char tty[MAXPATHLEN], *mytty;
+ const char *login;
+ int devfd;
(void)setlocale(LC_CTYPE, "");
+ devfd = open(_PATH_DEV, O_RDONLY);
+ if (devfd < 0)
+ err(1, "open(/dev)");
+ cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_LOOKUP,
+ CAP_PWRITE);
+ if (cap_rights_limit(devfd, &rights) < 0 && errno != ENOSYS)
+ err(1, "can't limit devfd rights");
+
+ /*
+ * Can't use capsicum helpers here because we need the additional
+ * FIODGNAME ioctl.
+ */
+ cap_rights_init(&rights, CAP_FCNTL, CAP_FSTAT, CAP_IOCTL, CAP_READ,
+ CAP_WRITE);
+ if ((cap_rights_limit(STDIN_FILENO, &rights) < 0 && errno != ENOSYS) ||
+ (cap_rights_limit(STDOUT_FILENO, &rights) < 0 && errno != ENOSYS) ||
+ (cap_rights_limit(STDERR_FILENO, &rights) < 0 && errno != ENOSYS) ||
+ (cap_ioctls_limit(STDIN_FILENO, cmds, nitems(cmds)) < 0 && errno != ENOSYS) ||
+ (cap_ioctls_limit(STDOUT_FILENO, cmds, nitems(cmds)) < 0 && errno != ENOSYS) ||
+ (cap_ioctls_limit(STDERR_FILENO, cmds, nitems(cmds)) < 0 && errno != ENOSYS) ||
+ (cap_fcntls_limit(STDIN_FILENO, CAP_FCNTL_GETFL) < 0 && errno != ENOSYS) ||
+ (cap_fcntls_limit(STDOUT_FILENO, CAP_FCNTL_GETFL) < 0 && errno != ENOSYS) ||
+ (cap_fcntls_limit(STDERR_FILENO, CAP_FCNTL_GETFL) < 0 && errno != ENOSYS))
+ err(1, "can't limit stdio rights");
+
+ caph_cache_catpages();
+ caph_cache_tzdata();
+
+ /*
+ * Cache UTX database fds.
+ */
+ setutxent();
+
+ /*
+ * Determine our login name before we reopen() stdout
+ * and before entering capability sandbox.
+ */
+ myuid = getuid();
+ if ((login = getlogin()) == NULL) {
+ if ((pwd = getpwuid(myuid)))
+ login = pwd->pw_name;
+ else
+ login = "???";
+ }
+
+ if (cap_enter() < 0 && errno != ENOSYS)
+ err(1, "cap_enter");
+
while (getopt(argc, argv, "") != -1)
usage();
argc -= optind;
@@ -99,29 +156,27 @@ main(int argc, char **argv)
errx(1, "can't find your tty's name");
if (!strncmp(mytty, _PATH_DEV, strlen(_PATH_DEV)))
mytty += strlen(_PATH_DEV);
- if (term_chk(mytty, &msgsok, &atime, 1))
+ if (term_chk(devfd, mytty, &msgsok, &atime, 1))
exit(1);
if (!msgsok)
errx(1, "you have write permission turned off");
- myuid = getuid();
-
/* check args */
switch (argc) {
case 1:
- search_utmp(argv[0], tty, mytty, myuid);
- do_write(tty, mytty, myuid);
+ search_utmp(devfd, argv[0], tty, mytty, myuid);
+ do_write(devfd, tty, mytty, login);
break;
case 2:
if (!strncmp(argv[1], _PATH_DEV, strlen(_PATH_DEV)))
argv[1] += strlen(_PATH_DEV);
if (utmp_chk(argv[0], argv[1]))
errx(1, "%s is not logged in on %s", argv[0], argv[1]);
- if (term_chk(argv[1], &msgsok, &atime, 1))
+ if (term_chk(devfd, argv[1], &msgsok, &atime, 1))
exit(1);
if (myuid && !msgsok)
errx(1, "%s has messages disabled on %s", argv[0], argv[1]);
- do_write(argv[1], mytty, myuid);
+ do_write(devfd, argv[1], mytty, login);
break;
default:
usage();
@@ -170,7 +225,7 @@ utmp_chk(char *user, char *tty)
* writing from, unless that's the only terminal with messages enabled.
*/
void
-search_utmp(char *user, char *tty, char *mytty, uid_t myuid)
+search_utmp(int devfd, char *user, char *tty, char *mytty, uid_t myuid)
{
struct utmpx *u;
time_t bestatime, atime;
@@ -185,7 +240,7 @@ search_utmp(char *user, char *tty, char
if (u->ut_type == USER_PROCESS &&
strcmp(user, u->ut_user) == 0) {
++nloggedttys;
- if (term_chk(u->ut_line, &msgsok, &atime, 0))
+ if (term_chk(devfd, u->ut_line, &msgsok, &atime, 0))
continue; /* bad term? skip */
if (myuid && !msgsok)
continue; /* skip ttys with msgs off */
@@ -219,15 +274,13 @@ search_utmp(char *user, char *tty, char
* and the access time
*/
int
-term_chk(char *tty, int *msgsokP, time_t *atimeP, int showerror)
+term_chk(int devfd, char *tty, int *msgsokP, time_t *atimeP, int showerror)
{
struct stat s;
- char path[MAXPATHLEN];
- (void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
- if (stat(path, &s) < 0) {
+ if (fstatat(devfd, tty, &s, 0) < 0) {
if (showerror)
- warn("%s", path);
+ warn("%s%s", _PATH_DEV, tty);
return(1);
}
*msgsokP = (s.st_mode & (S_IWRITE >> 3)) != 0; /* group write bit */
@@ -239,26 +292,21 @@ term_chk(char *tty, int *msgsokP, time_t
* do_write - actually make the connection
*/
void
-do_write(char *tty, char *mytty, uid_t myuid)
+do_write(int devfd, char *tty, char *mytty, const char *login)
{
- const char *login;
char *nows;
- struct passwd *pwd;
time_t now;
- char path[MAXPATHLEN], host[MAXHOSTNAMELEN];
+ char host[MAXHOSTNAMELEN];
wchar_t line[512];
+ int fd;
- /* Determine our login name before we reopen() stdout */
- if ((login = getlogin()) == NULL) {
- if ((pwd = getpwuid(myuid)))
- login = pwd->pw_name;
- else
- login = "???";
- }
-
- (void)snprintf(path, sizeof(path), "%s%s", _PATH_DEV, tty);
- if ((freopen(path, "w", stdout)) == NULL)
- err(1, "%s", path);
+ fd = openat(devfd, tty, O_WRONLY);
+ if (fd < 0)
+ err(1, "openat(%s%s)", _PATH_DEV, tty);
+ fclose(stdout);
+ stdout = fdopen(fd, "w");
+ if (stdout == NULL)
+ err(1, "%s%s", _PATH_DEV, tty);
(void)signal(SIGINT, done);
(void)signal(SIGHUP, done);
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