-/* $OpenBSD: auth2-pubkey.c,v 1.49 2015/05/04 06:10:48 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.50 2015/05/21 06:38:35 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
#include "monitor_wrap.h"
#include "authfile.h"
#include "match.h"
+#include "ssherr.h"
+#include "channels.h" /* XXX for session.h */
+#include "session.h" /* XXX for child_set_env(); refactor? */
/* import */
extern ServerOptions options;
free(extra);
}
+/*
+ * Splits 's' into an argument vector. Handles quoted string and basic
+ * escape characters (\\, \", \'). Caller must free the argument vector
+ * and its members.
+ */
+static int
+split_argv(const char *s, int *argcp, char ***argvp)
+{
+ int r = SSH_ERR_INTERNAL_ERROR;
+ int argc = 0, quote, i, j;
+ char *arg, **argv = xcalloc(1, sizeof(*argv));
+
+ *argvp = NULL;
+ *argcp = 0;
+
+ for (i = 0; s[i] != '\0'; i++) {
+ /* Skip leading whitespace */
+ if (s[i] == ' ' || s[i] == '\t')
+ continue;
+
+ /* Start of a token */
+ quote = 0;
+ if (s[i] == '\\' &&
+ (s[i + 1] == '\'' || s[i + 1] == '\"' || s[i + 1] == '\\'))
+ i++;
+ else if (s[i] == '\'' || s[i] == '"')
+ quote = s[i++];
+
+ argv = xreallocarray(argv, (argc + 2), sizeof(*argv));
+ arg = argv[argc++] = xcalloc(1, strlen(s + i) + 1);
+ argv[argc] = NULL;
+
+ /* Copy the token in, removing escapes */
+ for (j = 0; s[i] != '\0'; i++) {
+ if (s[i] == '\\') {
+ if (s[i + 1] == '\'' ||
+ s[i + 1] == '\"' ||
+ s[i + 1] == '\\') {
+ i++; /* Skip '\' */
+ arg[j++] = s[i];
+ } else {
+ /* Unrecognised escape */
+ arg[j++] = s[i];
+ }
+ } else if (quote == 0 && (s[i] == ' ' || s[i] == '\t'))
+ break; /* done */
+ else if (quote != 0 && s[i] == quote)
+ break; /* done */
+ else
+ arg[j++] = s[i];
+ }
+ if (s[i] == '\0') {
+ if (quote != 0) {
+ /* Ran out of string looking for close quote */
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ break;
+ }
+ }
+ /* Success */
+ *argcp = argc;
+ *argvp = argv;
+ argc = 0;
+ argv = NULL;
+ r = 0;
+ out:
+ if (argc != 0 && argv != NULL) {
+ for (i = 0; i < argc; i++)
+ free(argv[i]);
+ free(argv);
+ }
+ return r;
+}
+
+/*
+ * Reassemble an argument vector into a string, quoting and escaping as
+ * necessary. Caller must free returned string.
+ */
+static char *
+assemble_argv(int argc, char **argv)
+{
+ int i, j, ws, r;
+ char c, *ret;
+ struct sshbuf *buf, *arg;
+
+ if ((buf = sshbuf_new()) == NULL || (arg = sshbuf_new()) == NULL)
+ fatal("%s: sshbuf_new failed", __func__);
+
+ for (i = 0; i < argc; i++) {
+ ws = 0;
+ sshbuf_reset(arg);
+ for (j = 0; argv[i][j] != '\0'; j++) {
+ r = 0;
+ c = argv[i][j];
+ switch (c) {
+ case ' ':
+ case '\t':
+ ws = 1;
+ r = sshbuf_put_u8(arg, c);
+ break;
+ case '\\':
+ case '\'':
+ case '"':
+ if ((r = sshbuf_put_u8(arg, '\\')) != 0)
+ break;
+ /* FALLTHROUGH */
+ default:
+ r = sshbuf_put_u8(arg, c);
+ break;
+ }
+ if (r != 0)
+ fatal("%s: sshbuf_put_u8: %s",
+ __func__, ssh_err(r));
+ }
+ if ((i != 0 && (r = sshbuf_put_u8(buf, ' ')) != 0) ||
+ (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0) ||
+ (r = sshbuf_putb(buf, arg)) != 0 ||
+ (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0))
+ fatal("%s: buffer error: %s", __func__, ssh_err(r));
+ }
+ if ((ret = malloc(sshbuf_len(buf) + 1)) == NULL)
+ fatal("%s: malloc failed", __func__);
+ memcpy(ret, sshbuf_ptr(buf), sshbuf_len(buf));
+ ret[sshbuf_len(buf)] = '\0';
+ sshbuf_free(buf);
+ sshbuf_free(arg);
+ return ret;
+}
+
+/*
+ * Runs command in a subprocess. Returns pid on success and a FILE* to the
+ * subprocess' stdout or 0 on failure.
+ * NB. "command" is only used for logging.
+ */
+static pid_t
+subprocess(const char *tag, struct passwd *pw, const char *command,
+ int ac, char **av, FILE **child)
+{
+ FILE *f;
+ struct stat st;
+ int devnull, p[2], i;
+ pid_t pid;
+ char *cp, errmsg[512];
+ u_int envsize;
+ char **child_env;
+
+ *child = NULL;
+
+ debug3("%s: %s command \"%s\" running as %s", __func__,
+ tag, command, pw->pw_name);
+
+ /* Verify the path exists and is safe-ish to execute */
+ if (*av[0] != '/') {
+ error("%s path is not absolute", tag);
+ return 0;
+ }
+ temporarily_use_uid(pw);
+ if (stat(av[0], &st) < 0) {
+ error("Could not stat %s \"%s\": %s", tag,
+ av[0], strerror(errno));
+ restore_uid();
+ return 0;
+ }
+ if (auth_secure_path(av[0], &st, NULL, 0,
+ errmsg, sizeof(errmsg)) != 0) {
+ error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
+ restore_uid();
+ return 0;
+ }
+
+ /*
+ * Run the command; stderr is left in place, stdout is the
+ * authorized_keys output.
+ */
+ if (pipe(p) != 0) {
+ error("%s: pipe: %s", tag, strerror(errno));
+ restore_uid();
+ return 0;
+ }
+
+ /*
+ * Don't want to call this in the child, where it can fatal() and
+ * run cleanup_exit() code.
+ */
+ restore_uid();
+
+ switch ((pid = fork())) {
+ case -1: /* error */
+ error("%s: fork: %s", tag, strerror(errno));
+ close(p[0]);
+ close(p[1]);
+ return 0;
+ case 0: /* child */
+ /* Prepare a minimal environment for the child. */
+ envsize = 5;
+ child_env = xcalloc(sizeof(*child_env), envsize);
+ child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
+ child_set_env(&child_env, &envsize, "USER", pw->pw_name);
+ child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
+ child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
+ if ((cp = getenv("LANG")) != NULL)
+ child_set_env(&child_env, &envsize, "LANG", cp);
+
+ for (i = 0; i < NSIG; i++)
+ signal(i, SIG_DFL);
+
+ if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
+ error("%s: open %s: %s", tag, _PATH_DEVNULL,
+ strerror(errno));
+ _exit(1);
+ }
+ /* Keep stderr around a while longer to catch errors */
+ if (dup2(devnull, STDIN_FILENO) == -1 ||
+ dup2(p[1], STDOUT_FILENO) == -1) {
+ error("%s: dup2: %s", tag, strerror(errno));
+ _exit(1);
+ }
+ closefrom(STDERR_FILENO + 1);
+
+ /* Don't use permanently_set_uid() here to avoid fatal() */
+ if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
+ error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
+ strerror(errno));
+ _exit(1);
+ }
+ if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
+ error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
+ strerror(errno));
+ _exit(1);
+ }
+ /* stdin is pointed to /dev/null at this point */
+ if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
+ error("%s: dup2: %s", tag, strerror(errno));
+ _exit(1);
+ }
+
+ execve(av[0], av, child_env);
+ error("%s exec \"%s\": %s", tag, command, strerror(errno));
+ _exit(127);
+ default: /* parent */
+ break;
+ }
+
+ close(p[1]);
+ if ((f = fdopen(p[0], "r")) == NULL) {
+ error("%s: fdopen: %s", tag, strerror(errno));
+ close(p[0]);
+ /* Don't leave zombie child */
+ kill(pid, SIGTERM);
+ while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
+ ;
+ return 0;
+ }
+ /* Success */
+ debug3("%s: %s pid %ld", __func__, tag, (long)pid);
+ *child = f;
+ return pid;
+}
+
+/* Returns 0 if pid exited cleanly, non-zero otherwise */
+static int
+exited_cleanly(pid_t pid, const char *tag, const char *cmd)
+{
+ int status;
+
+ while (waitpid(pid, &status, 0) == -1) {
+ if (errno != EINTR) {
+ error("%s: waitpid: %s", tag, strerror(errno));
+ return -1;
+ }
+ }
+ if (WIFSIGNALED(status)) {
+ error("%s %s exited on signal %d", tag, cmd, WTERMSIG(status));
+ return -1;
+ } else if (WEXITSTATUS(status) != 0) {
+ error("%s %s failed, status %d", tag, cmd, WEXITSTATUS(status));
+ return -1;
+ }
+ return 0;
+}
+
static int
match_principals_option(const char *principal_list, struct sshkey_cert *cert)
{
static int
user_key_command_allowed2(struct passwd *user_pw, Key *key)
{
- FILE *f;
- int ok, found_key = 0;
+ FILE *f = NULL;
+ int r, ok, found_key = 0;
struct passwd *pw;
- struct stat st;
- int status, devnull, p[2], i;
+ int i, uid_swapped = 0, ac = 0;
pid_t pid;
- char *username, errmsg[512];
+ char *username = NULL, *key_fp = NULL, *keytext = NULL;
+ char *tmp, *command = NULL, **av = NULL;
+ void (*osigchld)(int);
- if (options.authorized_keys_command == NULL ||
- options.authorized_keys_command[0] != '/')
+ if (options.authorized_keys_command == NULL)
return 0;
-
if (options.authorized_keys_command_user == NULL) {
error("No user for AuthorizedKeysCommand specified, skipping");
return 0;
}
+ /*
+ * NB. all returns later this function should go via "out" to
+ * ensure the original SIGCHLD handler is restored properly.
+ */
+ osigchld = signal(SIGCHLD, SIG_DFL);
+
+ /* Prepare and verify the user for the command */
username = percent_expand(options.authorized_keys_command_user,
"u", user_pw->pw_name, (char *)NULL);
pw = getpwnam(username);
if (pw == NULL) {
error("AuthorizedKeysCommandUser \"%s\" not found: %s",
username, strerror(errno));
- free(username);
- return 0;
+ goto out;
}
- free(username);
-
- temporarily_use_uid(pw);
- if (stat(options.authorized_keys_command, &st) < 0) {
- error("Could not stat AuthorizedKeysCommand \"%s\": %s",
- options.authorized_keys_command, strerror(errno));
+ /* Prepare AuthorizedKeysCommand */
+ if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
+ SSH_FP_DEFAULT)) == NULL) {
+ error("%s: sshkey_fingerprint failed", __func__);
goto out;
}
- if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
- errmsg, sizeof(errmsg)) != 0) {
- error("Unsafe AuthorizedKeysCommand: %s", errmsg);
+ if ((r = sshkey_to_base64(key, &keytext)) != 0) {
+ error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
goto out;
}
- if (pipe(p) != 0) {
- error("%s: pipe: %s", __func__, strerror(errno));
+ /* Turn the command into an argument vector */
+ if (split_argv(options.authorized_keys_command, &ac, &av) != 0) {
+ error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
+ command);
goto out;
}
-
- debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"",
- options.authorized_keys_command, user_pw->pw_name, pw->pw_name);
+ if (ac == 0) {
+ error("AuthorizedKeysCommand \"%s\" yielded no arguments",
+ command);
+ goto out;
+ }
+ for (i = 1; i < ac; i++) {
+ tmp = percent_expand(av[i],
+ "u", user_pw->pw_name,
+ "h", user_pw->pw_dir,
+ "t", sshkey_ssh_name(key),
+ "f", key_fp,
+ "k", keytext,
+ (char *)NULL);
+ if (tmp == NULL)
+ fatal("%s: percent_expand failed", __func__);
+ free(av[i]);
+ av[i] = tmp;
+ }
+ /* Prepare a printable command for logs, etc. */
+ command = assemble_argv(ac, av);
/*
- * Don't want to call this in the child, where it can fatal() and
- * run cleanup_exit() code.
+ * If AuthorizedKeysCommand was run without arguments
+ * then fall back to the old behaviour of passing the
+ * target username as a single argument.
*/
- restore_uid();
-
- switch ((pid = fork())) {
- case -1: /* error */
- error("%s: fork: %s", __func__, strerror(errno));
- close(p[0]);
- close(p[1]);
- return 0;
- case 0: /* child */
- for (i = 0; i < NSIG; i++)
- signal(i, SIG_DFL);
-
- if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
- error("%s: open %s: %s", __func__, _PATH_DEVNULL,
- strerror(errno));
- _exit(1);
- }
- /* Keep stderr around a while longer to catch errors */
- if (dup2(devnull, STDIN_FILENO) == -1 ||
- dup2(p[1], STDOUT_FILENO) == -1) {
- error("%s: dup2: %s", __func__, strerror(errno));
- _exit(1);
- }
- closefrom(STDERR_FILENO + 1);
-
- /* Don't use permanently_set_uid() here to avoid fatal() */
- if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
- error("setresgid %u: %s", (u_int)pw->pw_gid,
- strerror(errno));
- _exit(1);
- }
- if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
- error("setresuid %u: %s", (u_int)pw->pw_uid,
- strerror(errno));
- _exit(1);
- }
- /* stdin is pointed to /dev/null at this point */
- if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
- error("%s: dup2: %s", __func__, strerror(errno));
- _exit(1);
- }
-
- execl(options.authorized_keys_command,
- options.authorized_keys_command, user_pw->pw_name, NULL);
-
- error("AuthorizedKeysCommand %s exec failed: %s",
- options.authorized_keys_command, strerror(errno));
- _exit(127);
- default: /* parent */
- break;
+ if (ac == 1) {
+ av = xreallocarray(av, ac + 2, sizeof(*av));
+ av[1] = xstrdup(user_pw->pw_name);
+ av[2] = NULL;
+ /* Fix up command too, since it is used in log messages */
+ free(command);
+ xasprintf(&command, "%s %s", av[0], av[1]);
}
+ if ((pid = subprocess("AuthorizedKeysCommand", pw, command,
+ ac, av, &f)) == 0)
+ goto out;
+
+ uid_swapped = 1;
temporarily_use_uid(pw);
- close(p[1]);
- if ((f = fdopen(p[0], "r")) == NULL) {
- error("%s: fdopen: %s", __func__, strerror(errno));
- close(p[0]);
- /* Don't leave zombie child */
- kill(pid, SIGTERM);
- while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
- ;
- goto out;
- }
ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
- fclose(f);
- while (waitpid(pid, &status, 0) == -1) {
- if (errno != EINTR) {
- error("%s: waitpid: %s", __func__, strerror(errno));
- goto out;
- }
- }
- if (WIFSIGNALED(status)) {
- error("AuthorizedKeysCommand %s exited on signal %d",
- options.authorized_keys_command, WTERMSIG(status));
- goto out;
- } else if (WEXITSTATUS(status) != 0) {
- error("AuthorizedKeysCommand %s returned status %d",
- options.authorized_keys_command, WEXITSTATUS(status));
+ if (exited_cleanly(pid, "AuthorizedKeysCommand", command) != 0)
goto out;
- }
+
+ /* Read completed successfully */
found_key = ok;
out:
- restore_uid();
+ if (f != NULL)
+ fclose(f);
+ signal(SIGCHLD, osigchld);
+ for (i = 0; i < ac; i++)
+ free(av[i]);
+ free(av);
+ if (uid_swapped)
+ restore_uid();
+ free(command);
+ free(username);
+ free(key_fp);
+ free(keytext);
return found_key;
}
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