Introduce pam_modutil_sanitize_helper_fds

This change introduces pam_modutil_sanitize_helper_fds - a new function
that redirects standard descriptors and closes all other descriptors.

pam_modutil_sanitize_helper_fds supports three types of input and output
redirection:
- PAM_MODUTIL_IGNORE_FD: do not redirect at all.
- PAM_MODUTIL_PIPE_FD: redirect to a pipe.  For stdin, it is implemented
  by creating a pipe, closing its write end, and redirecting stdin to
  its read end.  Likewise, for stdout/stderr it is implemented by
  creating a pipe, closing its read end, and redirecting to its write
  end.  Unlike stdin redirection, stdout/stderr redirection to a pipe
  has a side effect that a process writing to such descriptor should be
  prepared to handle SIGPIPE appropriately.
- PAM_MODUTIL_NULL_FD: redirect to /dev/null.  For stdin, it is
  implemented via PAM_MODUTIL_PIPE_FD because there is no functional
  difference.  For stdout/stderr, it is classic redirection to
  /dev/null.

PAM_MODUTIL_PIPE_FD is usually more suitable due to linux kernel
security restrictions, but when the helper process might be writing to
the corresponding descriptor and termination of the helper process by
SIGPIPE is not desirable, one should choose PAM_MODUTIL_NULL_FD.

* libpam/pam_modutil_sanitize.c: New file.
* libpam/Makefile.am (libpam_la_SOURCES): Add it.
* libpam/include/security/pam_modutil.h (pam_modutil_redirect_fd,
pam_modutil_sanitize_helper_fds): New declarations.
* libpam/libpam.map (LIBPAM_MODUTIL_1.1.9): New interface.
* modules/pam_exec/pam_exec.c (call_exec): Use
pam_modutil_sanitize_helper_fds.
* modules/pam_mkhomedir/pam_mkhomedir.c (create_homedir): Likewise.
* modules/pam_unix/pam_unix_acct.c (_unix_run_verify_binary): Likewise.
* modules/pam_unix/pam_unix_passwd.c (_unix_run_update_binary):
Likewise.
* modules/pam_unix/support.c (_unix_run_helper_binary): Likewise.
* modules/pam_xauth/pam_xauth.c (run_coprocess): Likewise.
* modules/pam_unix/support.h (MAX_FD_NO): Remove.

4 files changed, 28 insertions, 37 deletions

diff --git a/modules/pam_unix/pam_unix_acct.c b/modules/pam_unix/pam_unix_acct.c
index dc505e73..27998451 100644
--- a/modules/pam_unix/pam_unix_acct.c
+++ b/modules/pam_unix/pam_unix_acct.c
@@ -98,24 +98,21 @@ int _unix_run_verify_binary(pam_handle_t *pamh, unsigned int ctrl,
   /* fork */
   child = fork();
   if (child == 0) {
-    int i=0;
-    struct rlimit rlim;
     static char *envp[] = { NULL };
     const char *args[] = { NULL, NULL, NULL, NULL };
 
-    /* reopen stdout as pipe */
-    dup2(fds[1], STDOUT_FILENO);
-
     /* XXX - should really tidy up PAM here too */
 
-    if (getrlimit(RLIMIT_NOFILE,&rlim)==0) {
-      if (rlim.rlim_max >= MAX_FD_NO)
-        rlim.rlim_max = MAX_FD_NO;
-      for (i=0; i < (int)rlim.rlim_max; i++) {
-	if (i != STDOUT_FILENO) {
-	  close(i);
-	}
-      }
+    /* reopen stdout as pipe */
+    if (dup2(fds[1], STDOUT_FILENO) != STDOUT_FILENO) {
+      pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", "stdout");
+      _exit(PAM_AUTHINFO_UNAVAIL);
+    }
+
+    if (pam_modutil_sanitize_helper_fds(pamh, PAM_MODUTIL_PIPE_FD,
+					PAM_MODUTIL_IGNORE_FD,
+					PAM_MODUTIL_PIPE_FD) < 0) {
+      _exit(PAM_AUTHINFO_UNAVAIL);
     }
 
     if (geteuid() == 0) {
diff --git a/modules/pam_unix/pam_unix_passwd.c b/modules/pam_unix/pam_unix_passwd.c
index 5f3a3db3..606071ea 100644
--- a/modules/pam_unix/pam_unix_passwd.c
+++ b/modules/pam_unix/pam_unix_passwd.c
@@ -201,8 +201,6 @@ static int _unix_run_update_binary(pam_handle_t *pamh, unsigned int ctrl, const
     /* fork */
     child = fork();
     if (child == 0) {
-        int i=0;
-        struct rlimit rlim;
 	static char *envp[] = { NULL };
 	const char *args[] = { NULL, NULL, NULL, NULL, NULL, NULL };
         char buffer[16];
@@ -210,15 +208,15 @@ static int _unix_run_update_binary(pam_handle_t *pamh, unsigned int ctrl, const
 	/* XXX - should really tidy up PAM here too */
 
 	/* reopen stdin as pipe */
-	dup2(fds[0], STDIN_FILENO);
-
-	if (getrlimit(RLIMIT_NOFILE,&rlim)==0) {
-	  if (rlim.rlim_max >= MAX_FD_NO)
-	    rlim.rlim_max = MAX_FD_NO;
-	  for (i=0; i < (int)rlim.rlim_max; i++) {
-	    if (i != STDIN_FILENO)
-		close(i);
-	  }
+	if (dup2(fds[0], STDIN_FILENO) != STDIN_FILENO) {
+		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", "stdin");
+		_exit(PAM_AUTHINFO_UNAVAIL);
+	}
+
+	if (pam_modutil_sanitize_helper_fds(pamh, PAM_MODUTIL_IGNORE_FD,
+					    PAM_MODUTIL_PIPE_FD,
+					    PAM_MODUTIL_PIPE_FD) < 0) {
+		_exit(PAM_AUTHINFO_UNAVAIL);
 	}
 
 	/* exec binary helper */
diff --git a/modules/pam_unix/support.c b/modules/pam_unix/support.c
index 3a849c81..fdb45c20 100644
--- a/modules/pam_unix/support.c
+++ b/modules/pam_unix/support.c
@@ -564,23 +564,21 @@ static int _unix_run_helper_binary(pam_handle_t *pamh, const char *passwd,
     /* fork */
     child = fork();
     if (child == 0) {
-        int i=0;
-        struct rlimit rlim;
 	static char *envp[] = { NULL };
 	const char *args[] = { NULL, NULL, NULL, NULL };
 
 	/* XXX - should really tidy up PAM here too */
 
 	/* reopen stdin as pipe */
-	dup2(fds[0], STDIN_FILENO);
-
-	if (getrlimit(RLIMIT_NOFILE,&rlim)==0) {
-          if (rlim.rlim_max >= MAX_FD_NO)
-                rlim.rlim_max = MAX_FD_NO;
-	  for (i=0; i < (int)rlim.rlim_max; i++) {
-		if (i != STDIN_FILENO)
-		  close(i);
-	  }
+	if (dup2(fds[0], STDIN_FILENO) != STDIN_FILENO) {
+		pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", "stdin");
+		_exit(PAM_AUTHINFO_UNAVAIL);
+	}
+
+	if (pam_modutil_sanitize_helper_fds(pamh, PAM_MODUTIL_IGNORE_FD,
+					    PAM_MODUTIL_PIPE_FD,
+					    PAM_MODUTIL_PIPE_FD) < 0) {
+		_exit(PAM_AUTHINFO_UNAVAIL);
 	}
 
 	if (geteuid() == 0) {
diff --git a/modules/pam_unix/support.h b/modules/pam_unix/support.h
index 6f5b2eb6..cd6ddb76 100644
--- a/modules/pam_unix/support.h
+++ b/modules/pam_unix/support.h
@@ -141,8 +141,6 @@ static const UNIX_Ctrls unix_args[UNIX_CTRLS_] =
 
 #define UNIX_DEFAULTS  (unix_args[UNIX__NONULL].flag)
 
-#define MAX_FD_NO 2000000
-
 /* use this to free strings. ESPECIALLY password strings */
 
 #define _pam_delete(xx)		\