mount: add support for context, fscontext and defcontext selinux mount options

Signed-off-by: Karel Zak <kzak@redhat.com>

3 files changed, 146 insertions, 9 deletions

diff --git a/mount/Makefile.am b/mount/Makefile.am
index 6f0d403d9..bd2ff1c20 100644
--- a/mount/Makefile.am
+++ b/mount/Makefile.am
@@ -62,6 +62,9 @@ swapargs.h:
 clean-local:
 	rm -f swapargs.h
 
+if HAVE_SELINUX
+mount_LDADD += -lselinux
+endif
 
 install-exec-hook:
 	chmod 4755 $(DESTDIR)$(bindir)/mount
diff --git a/mount/mount.8 b/mount/mount.8
index 4692a42b3..8ed5a11b7 100644
--- a/mount/mount.8
+++ b/mount/mount.8
@@ -703,6 +703,50 @@ This option implies the options
 .BR noexec ", " nosuid ", and " nodev
 (unless overridden by subsequent options, as in the option line
 .BR users,exec,dev,suid ).
+.TP
+\fBcontext=\fP\fIcontext\fP, \fBfscontext=\fP\fIcontext\fP and \fBdefcontext=\fP\fIcontext\fP
+The
+.BR context=
+option is useful when mounting filesystems that do not support
+extended attributes, such as a floppy or hard disk formatted with VFAT, or
+systems that are not normally running under SELinux, such as an ext3 formatted
+disk from a non-SELinux workstation. You can also use
+.BR context=
+on filesystems you do not trust, such as a floppy. It also helps in compatibility with
+xattr-supporting filesystems on earlier 2.4.<x> kernel versions. Even where
+xattrs are supported, you can save time not having to label every file by
+assigning the entire disk one security context.
+
+A commonly used option for removable media is
+.BR context=system_u:object_r:removable_t .
+
+Two other options are
+.BR fscontext=
+and
+.BR defcontext= ,
+both of which are mutually exclusive of the context option. This means you
+can use fscontext and defcontext with each other, but neither can be used with
+context.
+
+The
+.BR fscontext=
+option works for all filesystems, regardless of their xattr
+support. The fscontext option sets the overarching filesystem label to a
+specific security context. This filesystem label is separate from the
+individual labels on the files. It represents the entire filesystem for
+certain kinds of permission checks, such as during mount or file creation.
+Individual file labels are still obtained from the xattrs on the files
+themselves. The context option actually sets the aggregate context that
+fscontext provides, in addition to supplying the same label for individual
+files.
+
+You can set the default security context for unlabeled files using
+.BR defcontext=
+option. This overrides the value set for unlabeled files in the policy and requires a
+file system that supports xattr labeling.
+
+For more details see
+.BR selinux (8)
 .RE
 .TP
 .B \-\-bind
diff --git a/mount/mount.c b/mount/mount.c
index 495eaed67..be2e4bfc6 100644
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -24,6 +24,11 @@
 #include <mntent.h>
 #include <paths.h>
 
+#ifdef HAVE_LIBSELINUX
+#include <selinux/selinux.h>
+#include <selinux/context.h>
+#endif
+
 #include "mount_blkid.h"
 #include "mount_constants.h"
 #include "sundries.h"
@@ -298,13 +303,71 @@ append_numopt(char *s, const char *opt, long num)
 	return append_opt(s, opt, buf);
 }
 
+#ifdef HAVE_LIBSELINUX
+/* strip quotes from a "string"
+ * Warning: This function modify the "str" argument.
+ */
+static char *
+strip_quotes(char *str)
+{
+	char *end = NULL;
+
+	if (*str != '"')
+		return str;
+
+	end = strrchr(str, '"');
+	if (end == NULL || end == str)
+		die (EX_USAGE, _("mount: improperly quoted option string '%s'"), str);
+
+	*end = '\0';
+	return str+1;
+}
+
+/* translates SELinux context from human to raw format and
+ * appends it to the mount extra options.
+ *
+ * returns -1 on error and 0 on success
+ */
+static int
+append_context(const char *optname, char *optdata, char **extra_opts)
+{
+	security_context_t raw = NULL;
+	char *data = NULL;
+
+	if (!is_selinux_enabled())
+		/* ignore the option if we running without selinux */
+		return 0;
+
+	if (optdata==NULL || *optdata=='\0' || optname==NULL)
+		return -1;
+
+	/* TODO: use strip_quotes() for all mount options? */
+	data = *optdata =='"' ? strip_quotes(optdata) : optdata;
+
+	if (selinux_trans_to_raw_context(
+			(security_context_t) data, &raw)==-1 ||
+			raw==NULL)
+		return -1;
+
+	if (verbose)
+		printf(_("mount: translated %s '%s' to '%s'\n"),
+				optname, data, (char *) raw);
+
+	*extra_opts = append_opt(*extra_opts, optname, NULL);
+	*extra_opts = xstrconcat4(*extra_opts, "\"", (char *) raw, "\"");
+
+	freecon(raw);
+	return 0;
+}
+#endif
+
 /*
  * Look for OPT in opt_map table and return mask value.
  * If OPT isn't found, tack it onto extra_opts (which is non-NULL).
  * For the options uid= and gid= replace user or group name by its value.
  */
 static inline void
-parse_opt(const char *opt, int *mask, char **extra_opts) {
+parse_opt(char *opt, int *mask, char **extra_opts) {
 	const struct opt_map *om;
 
 	for (om = opt_map; om->opt != NULL; om++)
@@ -348,6 +411,20 @@ parse_opt(const char *opt, int *mask, char **extra_opts) {
 		}
 	}
 
+#ifdef HAVE_LIBSELINUX
+	if (strncmp(opt, "context=", 8) == 0 && *(opt+8)) {
+		if (append_context("context=", opt+8, extra_opts) == 0)
+			return;
+	}
+	if (strncmp(opt, "fscontext=", 10) == 0 && *(opt+10)) {
+		if (append_context("fscontext=", opt+10, extra_opts) == 0)
+			return;
+	}
+	if (strncmp(opt, "defcontext=", 11) == 0 && *(opt+11)) {
+		if (append_context("defcontext=", opt+11, extra_opts) == 0)
+			return;
+	}
+#endif
 	*extra_opts = append_opt(*extra_opts, opt, NULL);
 }
 
@@ -362,12 +439,25 @@ parse_opts (const char *options, int *flags, char **extra_opts) {
 
 	if (options != NULL) {
 		char *opts = xstrdup(options);
-		char *opt;
-
-		for (opt = strtok(opts, ","); opt; opt = strtok(NULL, ","))
-			if (!parse_string_opt(opt))
-				parse_opt(opt, flags, extra_opts);
-
+		int open_quote = 0;
+		char *opt, *p;
+
+		for (p=opts, opt=NULL; p && *p; p++) {
+			if (!opt)
+				opt = p;		/* begin of the option item */
+			if (*p == '"')
+				open_quote ^= 1;	/* reverse the status */
+			if (open_quote)
+				continue;		/* still in quoted block */
+			if (*p == ',')
+				*p = '\0';		/* terminate the option item */
+			/* end of option item or last item */
+			if (*p == '\0' || *(p+1) == '\0') {
+				if (!parse_string_opt(opt))
+					parse_opt(opt, flags, extra_opts);
+				opt = NULL;
+			}
+		}
 		free(opts);
 	}
 
@@ -490,8 +580,8 @@ do_mount_syscall (struct mountargs *args) {
 	if ((flags & MS_MGC_MSK) == 0)
 		flags |= MS_MGC_VAL;
 
-	mnt_debug(1, "mount(2) syscall: source=\"%s\" target=\"%s\" "
-			"filesystemtype=\"%s\" mountflags=%lu data=\"%s\"",
+	mnt_debug(1, "mount(2) syscall: source: \"%s\", target: \"%s\", "
+			"filesystemtype: \"%s\", mountflags: %lu, data: %s",
 			args->spec, args->node, args->type, flags, (char *) args->data);
 
 	ret = mount (args->spec, args->node, args->type, flags, args->data);