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authormarkus@openbsd.org <markus@openbsd.org>2018-01-08 15:21:49 +0000
committerDamien Miller <djm@mindrot.org>2018-01-23 16:32:57 +1100
commit25cf9105b849932fc3b141590c009e704f2eeba6 (patch)
tree304d9af800f3450993741611dd28712928e61792 /auth.c
parentb0d34132b3ca26fe94013f01d7b92101e70b68bb (diff)
upstream commit
move subprocess() so scp/sftp do not need uidswap.o; ok djm@ OpenBSD-Commit-ID: 6601b8360388542c2e5fef0f4085f8e54750bea8
Diffstat (limited to 'auth.c')
-rw-r--r--auth.c155
1 files changed, 154 insertions, 1 deletions
diff --git a/auth.c b/auth.c
index a4490617..fd02eff0 100644
--- a/auth.c
+++ b/auth.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.c,v 1.124 2017/09/12 06:32:07 djm Exp $ */
+/* $OpenBSD: auth.c,v 1.125 2018/01/08 15:21:49 markus Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
@@ -28,6 +28,7 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
+#include <sys/wait.h>
#include <netinet/in.h>
@@ -840,3 +841,155 @@ auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
return dnsname;
}
}
+
+/*
+ * Runs command in a subprocess wuth a minimal environment.
+ * Returns pid on success, 0 on failure.
+ * The child stdout and stderr maybe captured, left attached or sent to
+ * /dev/null depending on the contents of flags.
+ * "tag" is prepended to log messages.
+ * NB. "command" is only used for logging; the actual command executed is
+ * av[0].
+ */
+pid_t
+subprocess(const char *tag, struct passwd *pw, const char *command,
+ int ac, char **av, FILE **child, u_int flags)
+{
+ FILE *f = NULL;
+ struct stat st;
+ int fd, devnull, p[2], i;
+ pid_t pid;
+ char *cp, errmsg[512];
+ u_int envsize;
+ char **child_env;
+
+ if (child != NULL)
+ *child = NULL;
+
+ debug3("%s: %s command \"%s\" running as %s (flags 0x%x)", __func__,
+ tag, command, pw->pw_name, flags);
+
+ /* Check consistency */
+ if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
+ (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
+ error("%s: inconsistent flags", __func__);
+ return 0;
+ }
+ if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
+ error("%s: inconsistent flags/output", __func__);
+ return 0;
+ }
+
+ /*
+ * If executing an explicit binary, then verify the it exists
+ * and appears 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 (safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
+ error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
+ restore_uid();
+ return 0;
+ }
+ /* Prepare to keep the child's stdout if requested */
+ if (pipe(p) != 0) {
+ error("%s: pipe: %s", tag, strerror(errno));
+ restore_uid();
+ return 0;
+ }
+ 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);
+ }
+ if (dup2(devnull, STDIN_FILENO) == -1) {
+ error("%s: dup2: %s", tag, strerror(errno));
+ _exit(1);
+ }
+
+ /* Set up stdout as requested; leave stderr in place for now. */
+ fd = -1;
+ if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
+ fd = p[1];
+ else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
+ fd = devnull;
+ if (fd != -1 && dup2(fd, 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 ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
+ 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 ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
+ close(p[0]);
+ else 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);
+ if (child != NULL)
+ *child = f;
+ return pid;
+}