[PATCH 2/2] mount: -T OTHERTAB support

[Isaac Dunham]

+0 bytes disabled, +56 enabled when DESKTOP is enabled (glibc/i386):
function                                             old     new   delta
.rodata                                           144949  144971     +22
packed_usage                                       30236   30256     +20
mount_main                                          1200    1214     +14
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 56/0)               Total: 56 bytes
   text	   data	    bss	    dec	    hex	filename
 757557	   2068	   9044	 768669	  bba9d	busybox_old
 757593	   2068	   9044	 768705	  bbac1	busybox_unstripped

Making fstabname always char* was tidier than the alternatives.
Should be +47 bytes without DESKTOP.
---
 util-linux/mount.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/util-linux/mount.c b/util-linux/mount.c
index 1e6a2c8..6e62882 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -105,6 +105,12 @@
 //config:	help
 //config:	  Support mount all and looking for files in /etc/fstab.
 //config:
+//config:config FEATURE_MOUNT_OTHERTAB
+//config:	depends on FEATURE_MOUNT_FSTAB
+//config:	bool "Support -T <alt_fstab>"
+//config:	default n
+//config:	help
+//config:	  Support mount -T (specifying an alternate fstab)
 //usage:#define mount_trivial_usage
 //usage:       "[OPTIONS] [-o OPTS] DEVICE NODE"
 //usage:#define mount_full_usage "\n\n"
@@ -131,6 +137,9 @@
 //usage:     "\n	-r		Read-only mount"
 //usage:     "\n	-w		Read-write mount (default)"
 //usage:     "\n	-t FSTYPE[,...]	Filesystem type(s)"
+//usage:	IF_FEATURE_MOUNT_OTHERTAB(
+//usage:     "\n	-T FSTAB	Read FSTAB instead of /etc/fstab"
+//usage:	)
 //usage:     "\n	-O OPT		Mount only filesystems with option OPT (-a only)"
 //usage:     "\n-o OPT:"
 //usage:	IF_FEATURE_MOUNT_LOOP(
@@ -255,7 +264,7 @@ enum {
 };
 
 
-#define OPTION_STR "o:t:rwanfvsiO:"
+#define OPTION_STR "o:t:rwanfvsiO:" IF_FEATURE_MOUNT_OTHERTAB("T:")
 enum {
 	OPT_o = (1 << 0),
 	OPT_t = (1 << 1),
@@ -268,6 +277,7 @@ enum {
 	OPT_s = (1 << 8),
 	OPT_i = (1 << 9),
 	OPT_O = (1 << 10),
+	OPT_T = (1 << 11),
 };
 
 #if ENABLE_FEATURE_MTAB_SUPPORT
@@ -2122,7 +2132,7 @@ int mount_main(int argc UNUSED_PARAM, char **argv)
 	char *O_optmatch = NULL;
 	char *storage_path;
 	llist_t *lst_o = NULL;
-	const char *fstabname;
+	char *fstabname = (char*)"/etc/fstab";
 	FILE *fstab;
 	int i, j;
 	int rc = EXIT_SUCCESS;
@@ -2149,12 +2159,17 @@ int mount_main(int argc UNUSED_PARAM, char **argv)
 	// Max 2 params; -o is a list, -v is a counter
 	opt_complementary = "?2o::" IF_FEATURE_MOUNT_VERBOSE("vv");
 	opt = getopt32(argv, OPTION_STR, &lst_o, &fstype, &O_optmatch
+			IF_FEATURE_MOUNT_OTHERTAB(, &fstabname)
 			IF_FEATURE_MOUNT_VERBOSE(, &verbose));
 	while (lst_o) append_mount_options(&cmdopts, llist_pop(&lst_o)); // -o
 	if (opt & OPT_r) append_mount_options(&cmdopts, "ro"); // -r
 	if (opt & OPT_w) append_mount_options(&cmdopts, "rw"); // -w
 	argv += optind;
 
+	// A malicious user could overmount /usr without this.
+	if (ENABLE_FEATURE_MOUNT_OTHERTAB && nonroot)
+		fstabname = (char*)"/etc/fstab";
+
 	// If we have no arguments, show currently mounted filesystems
 	if (!argv[0]) {
 		if (!(opt & OPT_a)) {
@@ -2217,12 +2232,11 @@ int mount_main(int argc UNUSED_PARAM, char **argv)
 	}
 
 	// Open either fstab or mtab
-	fstabname = "/etc/fstab";
 	if (cmdopt_flags & MS_REMOUNT) {
 		// WARNING. I am not sure this matches util-linux's
 		// behavior. It's possible util-linux does not
 		// take -o opts from mtab (takes only mount source).
-		fstabname = bb_path_mtab_file;
+		fstabname = (char*)bb_path_mtab_file;
 	}
 	fstab = setmntent(fstabname, "r");
 	if (!fstab)
-- 
2.1.4