[PATCH 1/4] make newrole suid

[PATCH 1/4] make newrole suid

[Michael C Thompson]

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This is the 1st of 4 patches.
This patch applies against policycoreutils-1.30.30-1.

Changes:
  * This patch breaks up the operations performed by newrole
    into functions. They are called in patch 2/4.
  * The following functions do not new functionality:
    - extract_pw_data
    - relabel_tty
    - restore_tty_label
    - parse_command_line_arguments
  * The following functions do add new functionality:
    - xsetenv
    - sanitize_environment
    - transition_to_caller_uid
    - set_signal_handles

The new (and existing) functionality should be adequately documented in 
the code. If it is not clear, I consider that to be a failure of the 
code, and please let me know.

Signed-off-by: Michael Thompson <thompsmc@us.ibm.com>


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diff -Naur policycoreutils-1.30.30/newrole/newrole.c policycoreutils-1.30.30.suid/newrole/newrole.c
--- policycoreutils-1.30.30/newrole/newrole.c	2006-09-29 10:50:27.000000000 -0500
+++ policycoreutils-1.30.30.suid/newrole/newrole.c	2006-10-06 16:58:06.000000000 -0500
@@ -101,6 +101,25 @@
 	return s2;
 }
 
+/**
+ * Returns zero on success, non-zero otherwise
+ */
+static int xsetenv(char const *name, char const *val)
+{
+	size_t namelen = strlen(name);
+	size_t vallen = strlen(val);
+	char *string = malloc(namelen + 1 + vallen + 1);
+
+	if (!string)
+		return -1;
+	strcpy(string, name);
+	string[namelen] = '=';
+	strcpy(string + namelen + 1, val);
+	if (putenv (string) != 0)
+		return -1;
+	return 0;
+}
+
 static char *build_new_range(char *newlevel, const char *range)
 {
 	char *newrangep = NULL;
@@ -332,6 +351,115 @@
 	return found;
 }
 
+/**
+ * Determine the Linux user identity to re-authenticate.
+ * If supported and set, use the login uid, as this should be more stable.
+ * Otherwise, use the real uid.
+ *
+ * This function assigns malloc'd memory into the pw_copy struct.
+ * Returns zero on success, non-zero otherwise
+ */
+int extract_pw_data(struct passwd *pw_copy)
+{
+	uid_t uid;
+	struct passwd *pw;
+
+#ifdef USE_AUDIT
+	uid = audit_getloginuid();
+	if (uid == (uid_t) - 1)
+		uid = getuid();
+#else
+	uid = getuid();
+#endif
+
+	setpwent();
+	pw = getpwuid(uid);
+	endpwent();
+	if (!(pw && pw->pw_name && pw->pw_name[0] && pw->pw_shell
+	      && pw->pw_shell[0] && pw->pw_dir && pw->pw_dir[0])) {
+		fprintf(stderr,
+			_("cannot find valid entry in the passwd file.\n"));
+		return -1;
+	}
+
+	*pw_copy = *pw;
+	pw = pw_copy;
+	pw->pw_name = xstrdup(pw->pw_name);
+	pw->pw_dir = xstrdup(pw->pw_dir);
+	pw->pw_shell = xstrdup(pw->pw_shell);
+
+	if (! (pw->pw_name && pw->pw_dir && pw->pw_shell))
+		goto out_free;
+
+	if (verify_shell(pw->pw_shell) == 0) {
+		fprintf(stderr, _("Error!  Shell is not valid.\n"));
+		goto out_free;
+	}
+	return 0;
+
+out_free:
+	free(pw->pw_name);
+	free(pw->pw_dir);
+	free(pw->pw_shell);
+	return -1;
+}
+
+/**
+ * Unset all environment variables except:
+ * TERM, DISPLAY and XAUTHORITY - if they are set, preserve values
+ * HOME, SHELL, USER and LOGNAME - set to contents of /etc/passwd
+ * PATH - set to default value DEFAULT_PATH
+ *
+ * Returns zero on success, non-zero otherwise
+ */
+static int sanitize_environment(const struct passwd *pw)
+{
+	char const *term_env = getenv("TERM");
+	char const *display_env = getenv("DISPLAY");
+	char const *xauthority_env = getenv("XAUTHORITY");
+	char *term = NULL;		/* temporary container */
+	char *display = NULL;		/* temporary container */
+	char *xauthority = NULL;	/* temporary container */
+	int rc;
+
+	/* Save the variable values we want */
+	if (term_env)
+		term = xstrdup(term_env);
+	if (display_env)
+		display = xstrdup(display_env);
+	if (xauthority_env)
+		xauthority = xstrdup(xauthority_env);
+	if ((term_env && !term) || (display_env && !display) ||
+	     (xauthority_env && !xauthority)) {
+		rc = -1;
+		goto out;
+	}
+
+	/* Clear everything from the env */
+	if ((rc = clearenv())) {
+		fprintf(stderr, _("Unable to clear environment\n"));
+		goto out;
+	}
+
+	/* Restore that which we saved */
+	if (term)
+		rc |= xsetenv("TERM", term);
+	if (display)
+		rc |= xsetenv("DISPLAY", display);
+	if (xauthority)
+		rc |= xsetenv("XAUTHORITY", xauthority);
+	rc |= xsetenv("HOME", pw->pw_dir);
+	rc |= xsetenv("SHELL", pw->pw_shell);
+	rc |= xsetenv("USER", pw->pw_name);
+	rc |= xsetenv("LOGNAME", pw->pw_name);
+	rc |= xsetenv("PATH", DEFAULT_PATH);
+out:
+	free(term);
+	free(display);
+	free(xauthority);
+	return rc;
+}
+
 /*
  * This function will drop the capabilities so that we are left
  * only with access to the audit system. If the user is root, we leave
@@ -396,6 +524,23 @@
 }
 #endif
 
+#ifdef NAMESPACE_PRIV
+/**
+ * This function will set the uid values to be that of caller's uid, and
+ * will drop any privilages which maybe have been raised.
+ */
+static int transition_to_caller_uid()
+{
+	uid_t uid = getuid();
+
+	if (setresuid(uid, uid, uid)) {
+		fprintf(stderr, _("Error changing uid, aborting.\n"));
+		return -1;
+	}
+	return 0;
+}
+#endif
+
 #ifdef LOG_AUDIT_PRIV
 /* Send audit message */
 static
@@ -443,6 +588,292 @@
 }
 #endif
 
+/**
+ * This function attempts to relabel the tty. If this function fails, then
+ * the fd is closed, the contexts are free'd and -1 is returned. On success,
+ * a valid fd is returned and tty_context and new_tty_context are set.
+ *
+ * This function will not fail if it can not relabel the tty when selinux is
+ * in permissive mode.
+ */
+static int relabel_tty(const char *ttyn, security_context_t new_context,
+			security_context_t *tty_context,
+			security_context_t *new_tty_context)
+{
+	int fd;
+	int enforcing = security_getenforce();
+	security_context_t tty_con = NULL;
+	security_context_t new_tty_con = NULL;
+
+	/* Re-open TTY descriptor */
+	fd = open(ttyn, O_RDWR);
+	if (fd < 0) {
+		fprintf(stderr, _("Error!  Could not open %s.\n"), ttyn);
+		return fd;
+	}
+
+	if (fgetfilecon(fd, &tty_con) < 0) {
+		fprintf(stderr, _("%s!  Could not get current context "
+			"for %s, not relabeling tty.\n"),
+			enforcing ? "Error" : "Warning", ttyn);
+		if (enforcing)
+			goto close_fd;
+	}
+
+	if (tty_con &&
+	    (security_compute_relabel(new_context, tty_con,
+				      SECCLASS_CHR_FILE, &new_tty_con) < 0)) {
+		fprintf(stderr,	_("%s!  Could not get new context for %s, "
+			"not relabeling tty.\n"),
+			enforcing ? "Error" : "Warning", ttyn);
+		if (enforcing)
+			goto close_fd;
+	}
+
+	if (new_tty_con)
+		if (fsetfilecon(fd, new_tty_con) < 0) {
+			fprintf(stderr,
+				_("%s!  Could not set new context for %s\n"),
+				enforcing ? "Error" : "Warning", ttyn);
+			freecon(new_tty_con);
+			new_tty_con = NULL;
+			if (enforcing)
+				goto close_fd;
+		}
+
+	*tty_context = tty_con;
+	*new_tty_context = new_tty_con;
+	return fd;
+
+close_fd:
+	freecon(tty_con);
+	close(fd);
+	return -1;
+}
+
+/**
+ * This function attempts to revert the relabeling done to the tty.
+ * fd   - referencing the opened ttyn
+ * ttyn - name of tty to restore
+ * tty_context     - original context of the tty
+ * new_tty_context - context tty was relabeled to
+ *
+ * Returns zero on success, non-zero otherwise
+ */
+static int restore_tty_label(int fd, const char *ttyn,
+			     security_context_t tty_context,
+			     security_context_t new_tty_context)
+{
+	int rc = 0;
+	security_context_t chk_tty_context = NULL;
+
+	if (!new_tty_context)
+		goto skip_relabel;
+
+	/* Verify that the tty still has the context set by newrole. */
+	if ((rc = fgetfilecon(fd, &chk_tty_context)) < 0) {
+		fprintf(stderr, "Could not fgetfilecon %s.\n", ttyn);
+		goto skip_relabel;
+	}
+
+	if ((rc = strcmp(chk_tty_context, new_tty_context))) {
+		fprintf(stderr, _("%s changed labels.\n"), ttyn);
+		goto skip_relabel;
+	}
+
+	if ((rc = fsetfilecon(fd, tty_context)) < 0)
+		fprintf(stderr,
+			_("Warning! Could not restore context for %s\n"), ttyn);
+skip_relabel:
+	freecon(chk_tty_context);
+	return rc;
+}
+
+/**
+ * Parses and validates the provided command line options and
+ * constructs a new context based on our old context and the
+ * arguments specified on the command line. On success
+ * new_context will be set to valid values, otherwise its value
+ * is left unchanged.
+ *
+ * Returns zero on success, non-zero otherwise.
+ */
+static int parse_command_line_arguments(int argc, char **argv, char *ttyn,
+					security_context_t old_context,
+					security_context_t *new_context)
+{
+	int flag_index;		/* flag index in argv[] */
+	int clflag;		/* holds codes for command line flags */
+	char *role_s = NULL;	/* role spec'd by user in argv[] */
+	char *type_s = NULL;	/* type spec'd by user in argv[] */
+	char *type_ptr = NULL;	/* stores malloc'd data from get_default_type */
+	char *level_s = NULL;	/* level spec'd by user in argv[] */
+	char *range_ptr = NULL;
+	security_context_t new_con = NULL;
+	context_t context = NULL; /* manipulatable form of new_context */
+	const struct option long_options[] = {
+		{"role", 1, 0, 'r'},
+		{"type", 1, 0, 't'},
+		{"level", 1, 0, 'l'},
+		{"version", 0, 0, 'V'},
+		{NULL, 0, 0, 0}
+	};
+
+	while (1) {
+		clflag = getopt_long(argc, argv, "r:t:l:V", long_options,
+				     &flag_index);
+		if (clflag == -1)
+			break;
+
+		switch (clflag) {
+		case 'V':
+			printf("newrole: %s version %s\n", PACKAGE, VERSION);
+			exit(0);
+			break;
+		case 'r':
+			if (role_s) {
+				fprintf(stderr,
+					_("Error: multiple roles specified\n"));
+				return -1;
+			}
+			role_s = optarg;
+			break;
+		case 't':
+			if (type_s) {
+				fprintf(stderr,
+					_("Error: multiple types specified\n"));
+				return -1;
+			}
+			type_s = optarg;
+			break;
+		case 'l':
+			if (!is_selinux_mls_enabled()) {
+				fprintf(stderr, _("Sorry, -l may be used with "
+					"SELinux MLS support.\n"));
+				return -1;
+			}
+			if (level_s) {
+				fprintf(stderr, _("Error: multiple levels "
+					"specified\n"));
+				return -1;
+			}
+			level_s = optarg;
+			break;
+		default:
+			fprintf(stderr, "%s\n", USAGE_STRING);
+			return -1;
+		}
+	}
+
+	/* Verify that the combination of command-line arguments are viable */
+	if (!(role_s || type_s || level_s)) {
+		fprintf(stderr, "%s\n", USAGE_STRING);
+		return -1;
+	}
+
+	/* Fill in a default type if one hasn't been specified. */
+	if (role_s && !type_s) {
+	 	/* get_default_type() returns malloc'd memory */
+		if (get_default_type(role_s, &type_ptr)) {
+			fprintf(stderr, _("Couldn't get default type.\n"));
+			send_audit_message(0, old_context, new_con, ttyn);
+			return -1;
+		}
+		type_s = type_ptr;
+	}
+
+	/* Create a temporary new context structure we extract and modify */
+	context = context_new(old_context);
+	if (!context) {
+		fprintf(stderr, _("failed to get new context.\n"));
+		goto err_free;
+	}
+
+	/* Modify the temporary new context */
+	if (role_s)
+		if (context_role_set(context, role_s)) {
+			fprintf(stderr, _("failed to set new role %s\n"),
+				role_s);
+			goto err_free;
+		}
+
+	if (type_s)
+		if (context_type_set(context, type_s)) {
+			fprintf(stderr, _("failed to set new type %s\n"),
+				type_s);
+			goto err_free;
+		}
+
+	if (level_s) {
+		range_ptr = build_new_range(level_s,context_range_get(context));
+		if (!range_ptr) {
+			fprintf(stderr,
+				_("failed to build new range with level %s\n"),
+				level_s);
+			goto err_free;
+		}
+		if (context_range_set(context, range_ptr)) {
+			fprintf(stderr, _("failed to set new range %s\n"),
+				range_ptr);
+			goto err_free;
+		}
+	}
+
+	/* Construct the final new context */
+	if (!(new_con = context_str(context))) {
+		fprintf(stderr, _("failed to convert new context to string\n"));
+		goto err_free;
+	}
+
+	if (security_check_context(new_con) < 0) {
+		fprintf(stderr, _("%s is not a valid context\n"), new_con);
+		send_audit_message(0, old_context, new_con, ttyn);
+		goto err_free;
+	}
+
+	*new_context = xstrdup(new_con);
+	if (!*new_context) {
+		fprintf(stderr, _("Unable to allocate memory for new_context"));
+		goto err_free;
+	}
+
+	free(type_ptr);
+	free(range_ptr);
+	context_free(context);
+	return 0;
+
+err_free:
+	free(type_ptr);
+	free(range_ptr);
+	freecon(new_con);
+	context_free(context);
+	return -1;
+}
+
+/**
+ * Take care of any signal setup
+ */
+static int set_signal_handles()
+{
+	sigset_t empty;
+
+	/* Empty the signal mask in case someone is blocking a signal */
+	if (sigemptyset(&empty)) {
+		fprintf(stderr, _("Unable to obtain empty signal set\n"));
+		return -1;
+	}
+
+	(void)sigprocmask(SIG_SETMASK, &empty, NULL);
+
+	/* Terminate on SIGHUP. */
+	if (signal(SIGHUP, SIG_DFL) == SIG_ERR) {
+		fprintf(stderr, _("Unable to set SIGHUP handler\n"));
+		return -1;
+	}
+
+	return 0;
+}
+
 /************************************************************************
  *
  * All code used for both PAM and shadow passwd goes in this section.

Re: [PATCH 1/4] make newrole suid

[Stephen Smalley]

On Fri, 2006-10-06 at 17:14 -0500, Michael C Thompson wrote:
> This is the 1st of 4 patches.
> This patch applies against policycoreutils-1.30.30-1.
> 
> Changes:
>   * This patch breaks up the operations performed by newrole
>     into functions. They are called in patch 2/4.
>   * The following functions do not new functionality:
>     - extract_pw_data
>     - relabel_tty
>     - restore_tty_label
>     - parse_command_line_arguments
>   * The following functions do add new functionality:
>     - xsetenv
>     - sanitize_environment
>     - transition_to_caller_uid
>     - set_signal_handles
> 
> The new (and existing) functionality should be adequately documented in 
> the code. If it is not clear, I consider that to be a failure of the 
> code, and please let me know.
> 
> Signed-off-by: Michael Thompson <thompsmc@us.ibm.com>

diff -Naur policycoreutils-1.30.30/newrole/newrole.c policycoreutils-1.30.30.suid/newrole/newrole.c
--- policycoreutils-1.30.30/newrole/newrole.c	2006-09-29 10:50:27.000000000 -0500
+++ policycoreutils-1.30.30.suid/newrole/newrole.c	2006-10-06 16:58:06.000000000 -0500
@@ -101,6 +101,25 @@
 	return s2;
 }
 
+/**
+ * Returns zero on success, non-zero otherwise
+ */
+static int xsetenv(char const *name, char const *val)
+{
+	size_t namelen = strlen(name);
+	size_t vallen = strlen(val);
+	char *string = malloc(namelen + 1 + vallen + 1);
+
+	if (!string)
+		return -1;
+	strcpy(string, name);
+	string[namelen] = '=';
+	strcpy(string + namelen + 1, val);
+	if (putenv (string) != 0)
+		return -1;

Why not just use setenv(name, val, 1)?  Then you also don't have to
worry about integer overflow in your string allocation.

@@ -332,6 +351,115 @@
 	return found;
 }
 
+/**
+ * Determine the Linux user identity to re-authenticate.
+ * If supported and set, use the login uid, as this should be more stable.
+ * Otherwise, use the real uid.
+ *
+ * This function assigns malloc'd memory into the pw_copy struct.
+ * Returns zero on success, non-zero otherwise
+ */
+int extract_pw_data(struct passwd *pw_copy)
+{
+	uid_t uid;
+	struct passwd *pw;
+
+#ifdef USE_AUDIT
+	uid = audit_getloginuid();
+	if (uid == (uid_t) - 1)
+		uid = getuid();
+#else
+	uid = getuid();
+#endif
+
+	setpwent();
+	pw = getpwuid(uid);
+	endpwent();
+	if (!(pw && pw->pw_name && pw->pw_name[0] && pw->pw_shell
+	      && pw->pw_shell[0] && pw->pw_dir && pw->pw_dir[0])) {

This seems unnecessary, unless the interface can actually return NULL
pointers for the individual fields (vs. empty strings, which are
possible) and unless later code cannot correctly handle the legal cases
that might be returned by the interface.  Otherwise, we end up
cluttering the code with lots of tests that might hide a real bug.

+		fprintf(stderr,
+			_("cannot find valid entry in the passwd file.\n"));
+		return -1;
+	}
+
+	*pw_copy = *pw;
+	pw = pw_copy;
+	pw->pw_name = xstrdup(pw->pw_name);
+	pw->pw_dir = xstrdup(pw->pw_dir);
+	pw->pw_shell = xstrdup(pw->pw_shell);
+
+	if (! (pw->pw_name && pw->pw_dir && pw->pw_shell))
+		goto out_free;

xstrdup by definition exits on OOM errors, so you don't have to re-test
here, or alternatively you don't need to use xstrdup in the first place
(vs. just plain strdup).

+static int sanitize_environment(const struct passwd *pw)
+{
+	char const *term_env = getenv("TERM");
+	char const *display_env = getenv("DISPLAY");
+	char const *xauthority_env = getenv("XAUTHORITY");
+	char *term = NULL;		/* temporary container */
+	char *display = NULL;		/* temporary container */
+	char *xauthority = NULL;	/* temporary container */
+	int rc;
+
+	/* Save the variable values we want */
+	if (term_env)
+		term = xstrdup(term_env);
+	if (display_env)
+		display = xstrdup(display_env);
+	if (xauthority_env)
+		xauthority = xstrdup(xauthority_env);
+	if ((term_env && !term) || (display_env && !display) ||
+	     (xauthority_env && !xauthority)) {
+		rc = -1;
+		goto out;
+	}

Same point here - you either use xstrdup and don't re-test afterward, or
you use strdup and test.  Ditto for all other uses of xstrdup.

@@ -396,6 +524,23 @@
 }
 #endif
 
+#ifdef NAMESPACE_PRIV
+/**
+ * This function will set the uid values to be that of caller's uid, and
+ * will drop any privilages which maybe have been raised.
+ */
+static int transition_to_caller_uid()
+{
+	uid_t uid = getuid();
+
+	if (setresuid(uid, uid, uid)) {
+		fprintf(stderr, _("Error changing uid, aborting.\n"));
+		return -1;
+	}

Note that this will not drop privileges if KEEPCAPS has been set to 1.
So you might want to explicitly call prctl in this function just prior
to calling setresuid to make it clear that you are dropping capabilities
as well.

-- 
Stephen Smalley
National Security Agency


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Re: [PATCH 1/4] make newrole suid

[Stephen Smalley]

On Tue, 2006-10-10 at 16:27 -0400, Stephen Smalley wrote:
> On Fri, 2006-10-06 at 17:14 -0500, Michael C Thompson wrote:
> +		fprintf(stderr,
> +			_("cannot find valid entry in the passwd file.\n"));
> +		return -1;
> +	}
> +
> +	*pw_copy = *pw;
> +	pw = pw_copy;
> +	pw->pw_name = xstrdup(pw->pw_name);
> +	pw->pw_dir = xstrdup(pw->pw_dir);
> +	pw->pw_shell = xstrdup(pw->pw_shell);
> +
> +	if (! (pw->pw_name && pw->pw_dir && pw->pw_shell))
> +		goto out_free;
> 
> xstrdup by definition exits on OOM errors, so you don't have to re-test
> here, or alternatively you don't need to use xstrdup in the first place
> (vs. just plain strdup).

Ok, I see that in patch 3, you drop the exit call from xstrdup.  Which I
think is a mistake - xmalloc/xstrdup-style functions typically mean
"succeed or exit".

-- 
Stephen Smalley
National Security Agency


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Re: [PATCH 1/4] make newrole suid

[Michael C Thompson]

Stephen Smalley wrote:
> On Tue, 2006-10-10 at 16:27 -0400, Stephen Smalley wrote:
>> On Fri, 2006-10-06 at 17:14 -0500, Michael C Thompson wrote:
>> +		fprintf(stderr,
>> +			_("cannot find valid entry in the passwd file.\n"));
>> +		return -1;
>> +	}
>> +
>> +	*pw_copy = *pw;
>> +	pw = pw_copy;
>> +	pw->pw_name = xstrdup(pw->pw_name);
>> +	pw->pw_dir = xstrdup(pw->pw_dir);
>> +	pw->pw_shell = xstrdup(pw->pw_shell);
>> +
>> +	if (! (pw->pw_name && pw->pw_dir && pw->pw_shell))
>> +		goto out_free;
>>
>> xstrdup by definition exits on OOM errors, so you don't have to re-test
>> here, or alternatively you don't need to use xstrdup in the first place
>> (vs. just plain strdup).
> 
> Ok, I see that in patch 3, you drop the exit call from xstrdup.  Which I
> think is a mistake - xmalloc/xstrdup-style functions typically mean
> "succeed or exit".

Right, I can see that now. I'll admit ignorance: I wasn't aware that was 
what the x prefix meant - I've never used that naming style before. I 
would rather not exit mid-code, so I'll change the use to be strdup and 
perform the checks.

Thanks,
Mike



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Re: [PATCH 1/4] make newrole suid

[Michael C Thompson]

Stephen Smalley wrote:
> On Fri, 2006-10-06 at 17:14 -0500, Michael C Thompson wrote:
>> This is the 1st of 4 patches.
>> This patch applies against policycoreutils-1.30.30-1.
>>
>> Changes:
>>   * This patch breaks up the operations performed by newrole
>>     into functions. They are called in patch 2/4.
>>   * The following functions do not new functionality:
>>     - extract_pw_data
>>     - relabel_tty
>>     - restore_tty_label
>>     - parse_command_line_arguments
>>   * The following functions do add new functionality:
>>     - xsetenv
>>     - sanitize_environment
>>     - transition_to_caller_uid
>>     - set_signal_handles
>>
>> The new (and existing) functionality should be adequately documented in 
>> the code. If it is not clear, I consider that to be a failure of the 
>> code, and please let me know.
>>
>> Signed-off-by: Michael Thompson <thompsmc@us.ibm.com>
> 
> diff -Naur policycoreutils-1.30.30/newrole/newrole.c policycoreutils-1.30.30.suid/newrole/newrole.c
> --- policycoreutils-1.30.30/newrole/newrole.c	2006-09-29 10:50:27.000000000 -0500
> +++ policycoreutils-1.30.30.suid/newrole/newrole.c	2006-10-06 16:58:06.000000000 -0500
> @@ -101,6 +101,25 @@
>  	return s2;
>  }
>  
> +/**
> + * Returns zero on success, non-zero otherwise
> + */
> +static int xsetenv(char const *name, char const *val)
> +{
> +	size_t namelen = strlen(name);
> +	size_t vallen = strlen(val);
> +	char *string = malloc(namelen + 1 + vallen + 1);
> +
> +	if (!string)
> +		return -1;
> +	strcpy(string, name);
> +	string[namelen] = '=';
> +	strcpy(string + namelen + 1, val);
> +	if (putenv (string) != 0)
> +		return -1;
> 
> Why not just use setenv(name, val, 1)?  Then you also don't have to
> worry about integer overflow in your string allocation.

I was following the source for su. That seems like a much better 
approach though. I will make this change.

> @@ -332,6 +351,115 @@
>  	return found;
>  }
>  
> +/**
> + * Determine the Linux user identity to re-authenticate.
> + * If supported and set, use the login uid, as this should be more stable.
> + * Otherwise, use the real uid.
> + *
> + * This function assigns malloc'd memory into the pw_copy struct.
> + * Returns zero on success, non-zero otherwise
> + */
> +int extract_pw_data(struct passwd *pw_copy)
> +{
> +	uid_t uid;
> +	struct passwd *pw;
> +
> +#ifdef USE_AUDIT
> +	uid = audit_getloginuid();
> +	if (uid == (uid_t) - 1)
> +		uid = getuid();
> +#else
> +	uid = getuid();
> +#endif
> +
> +	setpwent();
> +	pw = getpwuid(uid);
> +	endpwent();
> +	if (!(pw && pw->pw_name && pw->pw_name[0] && pw->pw_shell
> +	      && pw->pw_shell[0] && pw->pw_dir && pw->pw_dir[0])) {
> 
> This seems unnecessary, unless the interface can actually return NULL
> pointers for the individual fields (vs. empty strings, which are
> possible) and unless later code cannot correctly handle the legal cases
> that might be returned by the interface.  Otherwise, we end up
> cluttering the code with lots of tests that might hide a real bug.

We definately need to ensure that pw_name and pw_shell are valid. 
pw_name is used in pam_start and pw_shell is needed for executing the 
shell. It is possible to remove the pw_dir check, although it is used to 
set the HOME environment variable... not sure if that is important enough?

<snip>
> +#ifdef NAMESPACE_PRIV
> +/**
> + * This function will set the uid values to be that of caller's uid, and
> + * will drop any privilages which maybe have been raised.
> + */
> +static int transition_to_caller_uid()
> +{
> +	uid_t uid = getuid();
> +
> +	if (setresuid(uid, uid, uid)) {
> +		fprintf(stderr, _("Error changing uid, aborting.\n"));
> +		return -1;
> +	}
> 
> Note that this will not drop privileges if KEEPCAPS has been set to 1.
> So you might want to explicitly call prctl in this function just prior
> to calling setresuid to make it clear that you are dropping capabilities
> as well.

Right, KEEPCAPS is set to be 0 in all call paths in patch 3. Should it 
still be added / moved to this point for the sake of clarity? or is the 
current form (post 3rd patch) acceptable?

Thanks taking the time to review,
Mike



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