Add cwd_optional to command details and enable it in the sudoers plugin.

If cwd_optional is set to true, a failure to set the cwd will be a
warning, not an error, and the command will still run.
Debian bug #598519

NEWS

@@ -69,6 +69,11 @@ What's new in Sudo 1.9.0
    The list output also now includes the host name if one is present
    in the log file.
 
+ * For "sudo -i", if the target user's home directory does not
+   exist, sudo will now warn about the problem but run the command
+   in the current working directory.  Previously, this was a fatal
+   error.  Debian bug #598519
+
 What's new in Sudo 1.8.31p1
 
  * Sudo once again ignores a failure to restore the RLIMIT_CORE

doc/sudo_plugin.man.in

@@ -16,7 +16,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.TH "SUDO_PLUGIN" "5" "February 10, 2020" "Sudo @PACKAGE_VERSION@" "File Formats Manual"
+.TH "SUDO_PLUGIN" "5" "March 31, 2020" "Sudo @PACKAGE_VERSION@" "File Formats Manual"
 .nh
 .if n .ad l
 .SH "NAME"
@@ -886,6 +886,21 @@ Fully qualified path to the command to be executed.
 .TP 6n
 cwd=string
 The current working directory to change to when executing the command.
+If
+\fBsudo\fR
+is unable to change to the new working directory, the command will
+not be run unless
+\fIcwd_optional\fR
+is also set (see below).
+.TP 6n
+cwd_optional=bool
+If enabled,
+\fBsudo\fR
+will treat an inability to change to the new working directory as a
+non-fatal error.
+This setting has no effect unless
+\fIcwd\fR
+is also set.
 .TP 6n
 exec_background=bool
 By default,

doc/sudo_plugin.mdoc.in

@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd February 10, 2020
+.Dd March 31, 2020
 .Dt SUDO_PLUGIN @mansectform@
 .Os Sudo @PACKAGE_VERSION@
 .Sh NAME
@@ -789,6 +789,20 @@ or higher.
 Fully qualified path to the command to be executed.
 .It cwd=string
 The current working directory to change to when executing the command.
+If
+.Nm sudo
+is unable to change to the new working directory, the command will
+not be run unless
+.Em cwd_optional
+is also set (see below).
+.It cwd_optional=bool
+If enabled,
+.Nm sudo
+will treat an inability to change to the new working directory as a
+non-fatal error.
+This setting has no effect unless
+.Em cwd
+is also set.
 .It exec_background=bool
 By default,
 .Nm sudo

plugins/sudoers/policy.c

@@ -564,7 +564,7 @@ sudoers_policy_exec_setup(char *argv[], char *envp[], mode_t cmnd_umask,
 	debug_return_bool(true);	/* nothing to do */
 
     /* Increase the length of command_info as needed, it is *not* checked. */
-    command_info = calloc(52, sizeof(char *));
+    command_info = calloc(53, sizeof(char *));
     if (command_info == NULL)
 	goto oom;
 
@@ -619,6 +619,8 @@ sudoers_policy_exec_setup(char *argv[], char *envp[], mode_t cmnd_umask,
 	/* Set cwd to run user's homedir. */
 	if ((command_info[info_len++] = sudo_new_key_val("cwd", runas_pw->pw_dir)) == NULL)
 	    goto oom;
+	if ((command_info[info_len++] = strdup("cwd_optional=true")) == NULL)
+	    goto oom;
     }
     if ((command_info[info_len++] = sudo_new_key_val("runas_user", runas_pw->pw_name)) == NULL)
 	goto oom;

src/exec.c

@@ -214,12 +214,15 @@ exec_setup(struct command_details *details, int errfd)
      * specifies a different cwd.  Must be done after uid change.
      */
     if (details->cwd != NULL) {
-	if (details->chroot || user_details.cwd == NULL ||
+	if (details->chroot != NULL || user_details.cwd == NULL ||
 	    strcmp(details->cwd, user_details.cwd) != 0) {
 	    /* Note: cwd is relative to the new root, if any. */
-	    if (chdir(details->cwd) != 0) {
+	    if (chdir(details->cwd) == -1) {
 		sudo_warn(U_("unable to change directory to %s"), details->cwd);
-		goto done;
+		if (!details->cwd_optional)
+		    goto done;
+		if (details->chroot != NULL)
+		    sudo_warnx(U_("starting from %s"), "/");
 	    }
 	}
     }

src/sudo.c

@@ -678,6 +678,15 @@ command_info_to_details(char * const info[], struct command_details *details)
 		SET_STRING("chroot=", chroot)
 		SET_STRING("command=", command)
 		SET_STRING("cwd=", cwd)
+		if (strncmp("cwd_optional=", info[i], sizeof("cwd_optional=") - 1) == 0) {
+		    cp = info[i] + sizeof("cwd_optional=") - 1;
+		    details->cwd_optional = sudo_strtobool(cp);
+		    if (details->cwd_optional == -1) {
+			errno = EINVAL;
+			sudo_fatal("%s", info[i]);
+		    }
+		    break;
+		}
 		if (strncmp("closefrom=", info[i], sizeof("closefrom=") - 1) == 0) {
 		    cp = info[i] + sizeof("closefrom=") - 1;
 		    details->closefrom = sudo_strtonum(cp, 0, INT_MAX, &errstr);

src/sudo.h

@@ -157,6 +157,7 @@ struct command_details {
     int closefrom;
     int flags;
     int execfd;
+    int cwd_optional;
     struct preserved_fd_list preserved_fds;
     struct passwd *pw;
     GETGROUPS_T *groups;