[patch] New version of the patch to apply against 2.13.1.1

util-linux-2.13.1.1-symlink-mtab.patch (text/plain), 13.38 KB, created by Allen Fuller on 2008-08-05 19:16:28 UTC

diff -ur util-linux-ng-2.13.1.1/mount/fstab.c util-linux-ng-2.13.1.1-new/mount/fstab.c
--- util-linux-ng-2.13.1.1/mount/fstab.c	2008-08-05 09:55:06.000000000 -0700
+++ util-linux-ng-2.13.1.1-new/mount/fstab.c	2008-08-05 09:30:51.000000000 -0700
@@ -2,6 +2,8 @@
  * - added Native Language Support
  * Sun Mar 21 1999 - Arnaldo Carvalho de Melo <[e-mail]>
  * - fixed strerr(errno) in gettext calls
+ * 2003-08-08 Thomas Hood <[e-mail]> with help from Patrick McLean
+ * - Write through a symlink at /etc/mtab if it doesn't point into /proc/
  */
 
 #include <unistd.h>
@@ -13,59 +15,114 @@
 #include <time.h>
 #include "mount_mntent.h"
 #include "fstab.h"
+#include "realpath.h"
 #include "sundries.h"
 #include "xmalloc.h"
 #include "fsprobe.h"
 #include "mount_paths.h"
 #include "nls.h"
 
-#define streq(s, t)	(strcmp ((s), (t)) == 0)
-
-#define PROC_MOUNTS		"/proc/mounts"
-
+/* A 64 bit number can be displayed in 20 decimal digits */
+#define LEN_LARGEST_PID 20
+#define MTAB_PATH_MAX (PATH_MAX - (sizeof(MTAB_LOCK_SUFFIX) - 1) - LEN_LARGEST_PID)
 
 /* Information about mtab. ------------------------------------*/
-static int have_mtab_info = 0;
-static int var_mtab_does_not_exist = 0;
-static int var_mtab_is_a_symlink = 0;
+static char mtab_path[MTAB_PATH_MAX];
+static char mtab_lock_path[PATH_MAX];
+static char mtab_lock_targ[PATH_MAX];
+static char mtab_temp_path[PATH_MAX];
 
-static void
+/*
+ * Set mtab_path to the real path of the mtab file
+ * or to the null string if that path is inaccessible
+ *
+ * Run this early
+ */
+void
 get_mtab_info(void) {
 	struct stat mtab_stat;
 
-	if (!have_mtab_info) {
-		if (lstat(MOUNTED, &mtab_stat))
-			var_mtab_does_not_exist = 1;
-		else if (S_ISLNK(mtab_stat.st_mode))
-			var_mtab_is_a_symlink = 1;
-		have_mtab_info = 1;
+	if (lstat(MOUNTED, &mtab_stat)) {
+		/* Assume that the lstat error means that the file does not exist */
+		/* (Maybe we should check errno here) */
+		strcpy(mtab_path, MOUNTED);
+	} else if (S_ISLNK(mtab_stat.st_mode)) {
+		/* Is a symlink */
+		int len;
+		char *r = myrealpath(MOUNTED, mtab_path, MTAB_PATH_MAX);
+		mtab_path[MTAB_PATH_MAX - 1] = 0; /* Just to be sure */
+		len = strlen(mtab_path);
+		if (
+			r == NULL
+			|| len == 0
+			|| len >= (MTAB_PATH_MAX - 1)
+			|| streqn(mtab_path, PATH_PROC, sizeof(PATH_PROC) - 1)
+		) {
+			/* Real path invalid or inaccessible */
+			mtab_path[0] = '\0';
+			return;
+		}
+		/* mtab_path now contains mtab's real path */
+	} else {
+		/* Exists and is not a symlink */
+		strcpy(mtab_path, MOUNTED);
 	}
+
+	sprintf(mtab_lock_path, "%s%s", mtab_path, MTAB_LOCK_SUFFIX);
+	sprintf(mtab_lock_targ, "%s%s%d", mtab_path, MTAB_LOCK_SUFFIX, getpid());
+	sprintf(mtab_temp_path, "%s%s", mtab_path, MTAB_TEMP_SUFFIX);
 }
 
+
+/*
+ * Tell whether or not the mtab real path is accessible
+ *
+ * get_mtab_info() must have been run
+ */
+static int
+mtab_is_accessible(void) {
+	return (mtab_path[0] != '\0');
+}
+ 
+/*
+ * Tell whether or not the mtab file currently exists
+ *
+ * Note that the answer here is independent of whether or
+ * not the file is writable, so if you are planning to create
+ * the mtab file then check mtab_is_writable() too.
+ *
+ * get_mtab_info() must have been run
+ */
 int
 mtab_does_not_exist(void) {
-	get_mtab_info();
-	return var_mtab_does_not_exist;
-}
+	struct stat mtab_stat;
 
-static int
-mtab_is_a_symlink(void) {
-	get_mtab_info();
-	return var_mtab_is_a_symlink;
+	if (!mtab_is_accessible())
+		return 1;
+
+	if (lstat(mtab_path, &mtab_stat))
+		return 1;
+
+	return 0;
 }
 
+/*
+ * Tell whether or not mtab is writable (whether or not it currently exists)
+ *
+ * This depends on whether or not the real path is accessible and,
+ * if so, whether or not the file can be opened.  This function
+ * has the side effect of creating the file if it is writable.
+ *
+ * get_mtab_info() must have been run
+ */
 int
 mtab_is_writable() {
 	int fd;
 
-	/* Should we write to /etc/mtab upon an update?
-	   Probably not if it is a symlink to /proc/mounts, since that
-	   would create a file /proc/mounts in case the proc filesystem
-	   is not mounted. */
-	if (mtab_is_a_symlink())
+	if (!mtab_is_accessible())
 		return 0;
 
-	fd = open(MOUNTED, O_RDWR | O_CREAT, 0644);
+	fd = open(mtab_path, O_RDWR | O_CREAT, 0644);
 	if (fd >= 0) {
 		close(fd);
 		return 1;
@@ -161,21 +218,21 @@
 	got_mtab = 1;
 	mc->nxt = mc->prev = NULL;
 
-	fnam = MOUNTED;
+	fnam = mtab_path;
 	mfp = my_setmntent (fnam, "r");
 	if (mfp == NULL || mfp->mntent_fp == NULL) {
 		int errsv = errno;
-		fnam = PROC_MOUNTS;
+		fnam = PATH_PROC_MOUNTS;
 		mfp = my_setmntent (fnam, "r");
 		if (mfp == NULL || mfp->mntent_fp == NULL) {
 			error(_("warning: can't open %s: %s"),
-			      MOUNTED, strerror (errsv));
+			      mtab_path, strerror (errsv));
 			return;
 		}
 		if (verbose)
 			printf (_("mount: could not open %s - "
 				  "using %s instead\n"),
-				MOUNTED, PROC_MOUNTS);
+				mtab_path, PATH_PROC_MOUNTS);
 	}
 	read_mntentchn(mfp, fnam, mc);
 }
@@ -482,7 +539,7 @@
 	if (we_created_lockfile) {
 		close(lockfile_fd);
 		lockfile_fd = -1;
-		unlink (MOUNTED_LOCK);
+		unlink (mtab_lock_path);
 		we_created_lockfile = 0;
 	}
 }
@@ -501,12 +558,6 @@
    to delete the lock afterwards. Now the use of flock() is in principle
    superfluous, but avoids an arbitrary sleep(). */
 
-/* Where does the link point to? Obvious choices are mtab and mtab~~.
-   HJLu points out that the latter leads to races. Right now we use
-   mtab~.<pid> instead. Use 20 as upper bound for the length of %d. */
-#define MOUNTLOCK_LINKTARGET		MOUNTED_LOCK "%d"
-#define MOUNTLOCK_LINKTARGET_LTH	(sizeof(MOUNTED_LOCK)+20)
-
 /*
  * The original mount locking code has used sleep(1) between attempts and
  * maximal number of attemps has been 5.
@@ -533,7 +584,6 @@
 	int i;
 	struct timespec waittime;
 	struct timeval maxtime;
-	char linktargetfile[MOUNTLOCK_LINKTARGET_LTH];
 
 	at_die = unlock_mtab;
 
@@ -556,18 +606,16 @@
 		signals_have_been_setup = 1;
 	}
 
-	sprintf(linktargetfile, MOUNTLOCK_LINKTARGET, getpid ());
-
-	i = open (linktargetfile, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
+	i = open (mtab_lock_targ, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
 	if (i < 0) {
 		int errsv = errno;
-		/* linktargetfile does not exist (as a file)
+		/* mtab_lock_targ does not exist (as a file)
 		   and we cannot create it. Read-only filesystem?
 		   Too many files open in the system?
 		   Filesystem full? */
 		die (EX_FILEIO, _("can't create lock file %s: %s "
 						  "(use -n flag to override)"),
-			 linktargetfile, strerror (errsv));
+			 mtab_lock_targ, strerror (errsv));
 	}
 	close(i);
 
@@ -583,20 +631,20 @@
 		struct flock flock;
 		int errsv, j;
 
-		j = link(linktargetfile, MOUNTED_LOCK);
+		j = link(mtab_lock_targ, mtab_lock_path);
 		errsv = errno;
 
 		if (j == 0)
 			we_created_lockfile = 1;
 
 		if (j < 0 && errsv != EEXIST) {
-			(void) unlink(linktargetfile);
+			(void) unlink(mtab_lock_targ);
 			die (EX_FILEIO, _("can't link lock file %s: %s "
 			     "(use -n flag to override)"),
-			     MOUNTED_LOCK, strerror (errsv));
+			     mtab_lock_path, strerror (errsv));
 		}
 
-		lockfile_fd = open (MOUNTED_LOCK, O_WRONLY);
+		lockfile_fd = open (mtab_lock_path, O_WRONLY);
 
 		if (lockfile_fd < 0) {
 			/* Strange... Maybe the file was just deleted? */
@@ -606,10 +654,10 @@
 				we_created_lockfile = 0;
 				continue;
 			}
-			(void) unlink(linktargetfile);
+			(void) unlink(mtab_lock_targ);
 			die (EX_FILEIO, _("can't open lock file %s: %s "
 			     "(use -n flag to override)"),
-			     MOUNTED_LOCK, strerror (errsv));
+			     mtab_lock_path, strerror (errsv));
 		}
 
 		flock.l_type = F_WRLCK;
@@ -623,11 +671,11 @@
 				if (verbose) {
 				    int errsv = errno;
 				    printf(_("Can't lock lock file %s: %s\n"),
-					   MOUNTED_LOCK, strerror (errsv));
+					   mtab_lock_path, strerror (errsv));
 				}
 				/* proceed, since it was us who created the lockfile anyway */
 			}
-			(void) unlink(linktargetfile);
+			(void) unlink(mtab_lock_targ);
 		} else {
 			/* Someone else made the link. Wait. */
 			gettimeofday(&now, NULL);
@@ -635,19 +683,19 @@
 				alarm(maxtime.tv_sec - now.tv_sec);
 				if (fcntl (lockfile_fd, F_SETLKW, &flock) == -1) {
 					int errsv = errno;
-					(void) unlink(linktargetfile);
+					(void) unlink(mtab_lock_targ);
 					die (EX_FILEIO, _("can't lock lock file %s: %s"),
-					     MOUNTED_LOCK, (errno == EINTR) ?
+					     mtab_lock_path, (errno == EINTR) ?
 					     _("timed out") : strerror (errsv));
 				}
 				alarm(0);
 
 				nanosleep(&waittime, NULL);
 			} else {
-				(void) unlink(linktargetfile);
+				(void) unlink(mtab_lock_targ);
 				die (EX_FILEIO, _("Cannot create link %s\n"
 						  "Perhaps there is a stale lock file?\n"),
-					 MOUNTED_LOCK);
+					 mtab_lock_path);
 			}
 			close(lockfile_fd);
 		}
@@ -667,16 +715,16 @@
 void
 update_mtab (const char *dir, struct my_mntent *instead) {
 	mntFILE *mfp, *mftmp;
-	const char *fnam = MOUNTED;
+	const char *fnam = mtab_path;
 	struct mntentchn mtabhead;	/* dummy */
 	struct mntentchn *mc, *mc0, *absent = NULL;
 
-	if (mtab_does_not_exist() || !mtab_is_writable())
+	if (mtab_does_not_exist())
 		return;
 
 	lock_mtab();
 
-	/* having locked mtab, read it again */
+	/* having gotten the lock, we read mtab again */
 	mc0 = mc = &mtabhead;
 	mc->nxt = mc->prev = NULL;
 
@@ -733,11 +781,11 @@
 	}
 
 	/* write chain to mtemp */
-	mftmp = my_setmntent (MOUNTED_TEMP, "w");
+	mftmp = my_setmntent (mtab_temp_path, "w");
 	if (mftmp == NULL || mftmp->mntent_fp == NULL) {
 		int errsv = errno;
 		error (_("cannot open %s (%s) - mtab not updated"),
-		       MOUNTED_TEMP, strerror (errsv));
+		       mtab_temp_path, strerror (errsv));
 		discard_mntentchn(mc0);
 		goto leave;
 	}
@@ -746,7 +794,7 @@
 		if (my_addmntent(mftmp, &(mc->m)) == 1) {
 			int errsv = errno;
 			die (EX_FILEIO, _("error writing %s: %s"),
-			     MOUNTED_TEMP, strerror (errsv));
+			     mtab_temp_path, strerror (errsv));
 		}
 	}
 
@@ -756,25 +804,25 @@
 		    S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH) < 0) {
 		int errsv = errno;
 		fprintf(stderr, _("error changing mode of %s: %s\n"),
-			MOUNTED_TEMP, strerror (errsv));
+			mtab_temp_path, strerror (errsv));
 	}
 	my_endmntent (mftmp);
 
 	{ /*
 	   * If mount is setuid and some non-root user mounts sth,
-	   * then mtab.tmp might get the group of this user. Copy uid/gid
-	   * from the present mtab before renaming.
+	   * then the temp file might get the group of this user.
+	   * Copy uid/gid from the present mtab before renaming.
 	   */
 	    struct stat sbuf;
-	    if (stat (MOUNTED, &sbuf) == 0)
-		chown (MOUNTED_TEMP, sbuf.st_uid, sbuf.st_gid);
+	    if (stat (mtab_path, &sbuf) == 0)
+		chown (mtab_temp_path, sbuf.st_uid, sbuf.st_gid);
 	}
 
 	/* rename mtemp to mtab */
-	if (rename (MOUNTED_TEMP, MOUNTED) < 0) {
+	if (rename (mtab_temp_path, mtab_path) < 0) {
 		int errsv = errno;
 		fprintf(stderr, _("can't rename %s to %s: %s\n"),
-			MOUNTED_TEMP, MOUNTED, strerror(errsv));
+			mtab_temp_path, mtab_path, strerror(errsv));
 	}
 
  leave:
diff -ur util-linux-ng-2.13.1.1/mount/mount.c util-linux-ng-2.13.1.1-new/mount/mount.c
--- util-linux-ng-2.13.1.1/mount/mount.c	2008-08-05 09:55:06.000000000 -0700
+++ util-linux-ng-2.13.1.1-new/mount/mount.c	2008-08-05 09:43:24.000000000 -0700
@@ -519,7 +519,11 @@
 	return ret;
 }
 
-/* Create mtab with a root entry.  */
+/*
+ * Create mtab with a root entry.
+ *
+ * Caller should check that mtab is writable first
+ */
 static void
 create_mtab (void) {
 	struct mntentchn *fstab;
@@ -1813,6 +1817,9 @@
 	initproctitle(argc, argv);
 #endif
 
+	get_mtab_info();
+	/* Keep in mind that /etc/mtab may be a symlink */
+
 	while ((c = getopt_long (argc, argv, "afFhilL:no:O:p:rsU:vVwt:",
 				 longopts, NULL)) != -1) {
 		switch (c) {
@@ -1970,7 +1977,7 @@
 			die (EX_USAGE, _("mount: only root can do that"));
 	}
 
-	if (!nomtab && mtab_does_not_exist()) {
+	if (!nomtab && mtab_does_not_exist() && mtab_is_writable()) {
 		if (verbose > 1)
 			printf(_("mount: no %s found - creating it..\n"),
 			       MOUNTED);
diff -ur util-linux-ng-2.13.1.1/mount/mount_paths.h util-linux-ng-2.13.1.1-new/mount/mount_paths.h
--- util-linux-ng-2.13.1.1/mount/mount_paths.h	2008-08-05 09:55:06.000000000 -0700
+++ util-linux-ng-2.13.1.1-new/mount/mount_paths.h	2008-08-05 09:49:51.000000000 -0700
@@ -4,7 +4,12 @@
 #include <mntent.h>
 
 #define _PATH_FSTAB	"/etc/fstab"
-#define PROC_SWAPS      "/proc/swaps"
+#define PATH_PROC	"/proc/"
+#define PROC_SWAPS      PATH_PROC "swaps"
+#define PATH_PROC_MOUNTS      PATH_PROC "mounts"
+
+#define MTAB_LOCK_SUFFIX	"~"
+#define MTAB_TEMP_SUFFIX	".tmp"
 
 #ifdef _PATH_MOUNTED
 # define MOUNTED_LOCK	_PATH_MOUNTED "~"
diff -ur util-linux-ng-2.13.1.1/mount/sundries.h util-linux-ng-2.13.1.1-new/mount/sundries.h
--- util-linux-ng-2.13.1.1/mount/sundries.h	2008-08-05 09:55:06.000000000 -0700
+++ util-linux-ng-2.13.1.1-new/mount/sundries.h	2008-08-05 09:12:19.000000000 -0700
@@ -21,6 +21,7 @@
 extern int sloppy;
 
 #define streq(s, t)	(strcmp ((s), (t)) == 0)
+#define streqn(s, t, n)	(strncmp((s), (t), (n)) == 0)
 
 /* Functions in sundries.c that are used in mount.c and umount.c  */ 
 void block_signals (int how);
diff -ur util-linux-ng-2.13.1.1/mount/umount.c util-linux-ng-2.13.1.1-new/mount/umount.c
--- util-linux-ng-2.13.1.1/mount/umount.c	2008-08-05 09:55:06.000000000 -0700
+++ util-linux-ng-2.13.1.1-new/mount/umount.c	2008-08-05 09:13:39.000000000 -0700
@@ -574,6 +574,8 @@
 
 	umask(022);
 
+	get_mtab_info();
+
 	while ((c = getopt_long (argc, argv, "adfhlnrit:O:vV",
 				 longopts, NULL)) != -1)
 		switch (c) {