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281 lines
8.2 KiB
281 lines
8.2 KiB
diff --git a/gss-serv-krb5.c b/gss-serv-krb5.c
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index 413b845..54dd383 100644
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--- a/gss-serv-krb5.c
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+++ b/gss-serv-krb5.c
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@@ -32,7 +32,9 @@
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#include <sys/types.h>
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#include <stdarg.h>
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+#include <stdio.h>
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#include <string.h>
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+#include <unistd.h>
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#include "xmalloc.h"
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#include "sshkey.h"
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@@ -45,6 +47,7 @@
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#include "ssh-gss.h"
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+extern Authctxt *the_authctxt;
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extern ServerOptions options;
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#ifdef HEIMDAL
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@@ -56,6 +59,13 @@ extern ServerOptions options;
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# include <gssapi/gssapi_krb5.h>
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#endif
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+/* all commands are allowed by default */
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+char **k5users_allowed_cmds = NULL;
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+
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+static int ssh_gssapi_k5login_exists();
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+static int ssh_gssapi_krb5_cmdok(krb5_principal, const char *, const char *,
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+ int);
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+
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static krb5_context krb_context = NULL;
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/* Initialise the krb5 library, for the stuff that GSSAPI won't do */
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@@ -88,6 +98,7 @@ ssh_gssapi_krb5_userok(ssh_gssapi_client *client, char *name)
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krb5_principal princ;
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int retval;
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const char *errmsg;
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+ int k5login_exists;
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if (ssh_gssapi_krb5_init() == 0)
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return 0;
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@@ -99,10 +110,22 @@ ssh_gssapi_krb5_userok(ssh_gssapi_client *client, char *name)
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krb5_free_error_message(krb_context, errmsg);
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return 0;
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}
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- if (krb5_kuserok(krb_context, princ, name)) {
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+ /* krb5_kuserok() returns 1 if .k5login DNE and this is self-login.
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+ * We have to make sure to check .k5users in that case. */
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+ k5login_exists = ssh_gssapi_k5login_exists();
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+ /* NOTE: .k5login and .k5users must opened as root, not the user,
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+ * because if they are on a krb5-protected filesystem, user credentials
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+ * to access these files aren't available yet. */
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+ if (krb5_kuserok(krb_context, princ, name) && k5login_exists) {
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retval = 1;
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logit("Authorized to %s, krb5 principal %s (krb5_kuserok)",
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name, (char *)client->displayname.value);
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+ } else if (ssh_gssapi_krb5_cmdok(princ, client->exportedname.value,
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+ name, k5login_exists)) {
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+ retval = 1;
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+ logit("Authorized to %s, krb5 principal %s "
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+ "(ssh_gssapi_krb5_cmdok)",
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+ name, (char *)client->displayname.value);
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} else
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retval = 0;
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@@ -110,6 +133,137 @@ ssh_gssapi_krb5_userok(ssh_gssapi_client *client, char *name)
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return retval;
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}
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+/* Test for existence of .k5login.
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+ * We need this as part of our .k5users check, because krb5_kuserok()
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+ * returns success if .k5login DNE and user is logging in as himself.
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+ * With .k5login absent and .k5users present, we don't want absence
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+ * of .k5login to authorize self-login. (absence of both is required)
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+ * Returns 1 if .k5login is available, 0 otherwise.
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+ */
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+static int
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+ssh_gssapi_k5login_exists()
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+{
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+ char file[MAXPATHLEN];
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+ struct passwd *pw = the_authctxt->pw;
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+
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+ snprintf(file, sizeof(file), "%s/.k5login", pw->pw_dir);
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+ return access(file, F_OK) == 0;
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+}
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+
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+/* check .k5users for login or command authorization
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+ * Returns 1 if principal is authorized, 0 otherwise.
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+ * If principal is authorized, (global) k5users_allowed_cmds may be populated.
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+ */
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+static int
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+ssh_gssapi_krb5_cmdok(krb5_principal principal, const char *name,
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+ const char *luser, int k5login_exists)
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+{
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+ FILE *fp;
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+ char file[MAXPATHLEN];
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+ char *line = NULL;
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+ char kuser[65]; /* match krb5_kuserok() */
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+ struct stat st;
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+ struct passwd *pw = the_authctxt->pw;
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+ int found_principal = 0;
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+ int ncommands = 0, allcommands = 0;
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+ u_long linenum = 0;
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+ size_t linesize = 0;
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+
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+ snprintf(file, sizeof(file), "%s/.k5users", pw->pw_dir);
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+ /* If both .k5login and .k5users DNE, self-login is ok. */
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+ if (!k5login_exists && (access(file, F_OK) == -1)) {
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+ return (krb5_aname_to_localname(krb_context, principal,
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+ sizeof(kuser), kuser) == 0) &&
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+ (strcmp(kuser, luser) == 0);
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+ }
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+ if ((fp = fopen(file, "r")) == NULL) {
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+ int saved_errno = errno;
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+ /* 2nd access check to ease debugging if file perms are wrong.
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+ * But we don't want to report this if .k5users simply DNE. */
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+ if (access(file, F_OK) == 0) {
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+ logit("User %s fopen %s failed: %s",
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+ pw->pw_name, file, strerror(saved_errno));
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+ }
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+ return 0;
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+ }
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+ /* .k5users must be owned either by the user or by root */
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+ if (fstat(fileno(fp), &st) == -1) {
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+ /* can happen, but very wierd error so report it */
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+ logit("User %s fstat %s failed: %s",
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+ pw->pw_name, file, strerror(errno));
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+ fclose(fp);
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+ return 0;
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+ }
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+ if (!(st.st_uid == pw->pw_uid || st.st_uid == 0)) {
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+ logit("User %s %s is not owned by root or user",
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+ pw->pw_name, file);
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+ fclose(fp);
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+ return 0;
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+ }
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+ /* .k5users must be a regular file. krb5_kuserok() doesn't do this
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+ * check, but we don't want to be deficient if they add a check. */
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+ if (!S_ISREG(st.st_mode)) {
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+ logit("User %s %s is not a regular file", pw->pw_name, file);
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+ fclose(fp);
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+ return 0;
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+ }
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+ /* file exists; initialize k5users_allowed_cmds (to none!) */
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+ k5users_allowed_cmds = xcalloc(++ncommands,
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+ sizeof(*k5users_allowed_cmds));
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+
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+ /* Check each line. ksu allows unlimited length lines. */
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+ while (!allcommands && getline(&line, &linesize, fp) != -1) {
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+ linenum++;
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+ char *token;
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+
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+ /* we parse just like ksu, even though we could do better */
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+ if ((token = strtok(line, " \t\n")) == NULL)
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+ continue;
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+ if (strcmp(name, token) == 0) {
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+ /* we matched on client principal */
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+ found_principal = 1;
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+ if ((token = strtok(NULL, " \t\n")) == NULL) {
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+ /* only shell is allowed */
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+ k5users_allowed_cmds[ncommands-1] =
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+ xstrdup(pw->pw_shell);
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+ k5users_allowed_cmds =
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+ xreallocarray(k5users_allowed_cmds, ++ncommands,
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+ sizeof(*k5users_allowed_cmds));
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+ break;
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+ }
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+ /* process the allowed commands */
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+ while (token) {
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+ if (strcmp(token, "*") == 0) {
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+ allcommands = 1;
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+ break;
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+ }
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+ k5users_allowed_cmds[ncommands-1] =
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+ xstrdup(token);
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+ k5users_allowed_cmds =
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+ xreallocarray(k5users_allowed_cmds, ++ncommands,
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+ sizeof(*k5users_allowed_cmds));
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+ token = strtok(NULL, " \t\n");
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+ }
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+ }
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+ }
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+ free(line);
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+ if (k5users_allowed_cmds) {
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+ /* terminate vector */
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+ k5users_allowed_cmds[ncommands-1] = NULL;
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+ /* if all commands are allowed, free vector */
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+ if (allcommands) {
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+ int i;
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+ for (i = 0; i < ncommands; i++) {
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+ free(k5users_allowed_cmds[i]);
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+ }
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+ free(k5users_allowed_cmds);
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+ k5users_allowed_cmds = NULL;
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+ }
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+ }
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+ fclose(fp);
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+ return found_principal;
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+}
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+
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/* This writes out any forwarded credentials from the structure populated
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* during userauth. Called after we have setuid to the user */
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diff --git a/session.c b/session.c
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index 28659ec..9c94d8e 100644
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--- a/session.c
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+++ b/session.c
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@@ -789,6 +789,29 @@ do_exec(Session *s, const char *command)
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command = auth_opts->force_command;
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forced = "(key-option)";
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}
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+#ifdef GSSAPI
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+#ifdef KRB5 /* k5users_allowed_cmds only available w/ GSSAPI+KRB5 */
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+ else if (k5users_allowed_cmds) {
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+ const char *match = command;
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+ int allowed = 0, i = 0;
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+
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+ if (!match)
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+ match = s->pw->pw_shell;
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+ while (k5users_allowed_cmds[i]) {
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+ if (strcmp(match, k5users_allowed_cmds[i++]) == 0) {
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+ debug("Allowed command '%.900s'", match);
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+ allowed = 1;
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+ break;
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+ }
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+ }
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+ if (!allowed) {
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+ debug("command '%.900s' not allowed", match);
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+ return 1;
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+ }
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+ }
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+#endif
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+#endif
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+
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s->forced = 0;
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if (forced != NULL) {
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s->forced = 1;
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diff --git a/ssh-gss.h b/ssh-gss.h
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index 0374c88..509109a 100644
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--- a/ssh-gss.h
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+++ b/ssh-gss.h
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@@ -49,6 +49,10 @@
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# endif /* !HAVE_DECL_GSS_C_NT_... */
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# endif /* !HEIMDAL */
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+
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+/* .k5users support */
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+extern char **k5users_allowed_cmds;
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+
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#endif /* KRB5 */
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/* draft-ietf-secsh-gsskeyex-06 */
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diff --git a/sshd.8 b/sshd.8
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index adcaaf9..824163b 100644
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--- a/sshd.8
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+++ b/sshd.8
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@@ -324,6 +324,7 @@ Finally, the server and the client enter an authentication dialog.
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The client tries to authenticate itself using
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host-based authentication,
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public key authentication,
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+GSSAPI authentication,
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challenge-response authentication,
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or password authentication.
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.Pp
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@@ -800,6 +801,12 @@ This file is used in exactly the same way as
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but allows host-based authentication without permitting login with
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rlogin/rsh.
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.Pp
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+.It Pa ~/.k5login
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+.It Pa ~/.k5users
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+These files enforce GSSAPI/Kerberos authentication access control.
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+Further details are described in
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+.Xr ksu 1 .
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+.Pp
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.It Pa ~/.ssh/
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This directory is the default location for all user-specific configuration
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and authentication information.
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