util-linux/util-linux-2.13.1-prevent_loop_mounting_the_same_file_twice.patch

commit 2368077223fa5800cf88659c9c57a7f6517f3fad
Author: Karel Zak <kzak@redhat.com>
Date:   Tue Sep 11 14:35:34 2007 +0200

    mount: prevent loop mounting the same file twice
    
    The mount syscall prevents mounting the same device twice
    to the same mountpoint. When loop mounting a file, for each
    file a new loop device gets allocated, which prevents the detection
    of loop mounting the same file to the same mountpoint twice.
    The patch adds a check to prevent double mounts, if the same loopfile
    is going to be mounted with the same offset to the same mountpoint.
    
    Co-Author: Matthias Koenig <mkoenig@suse.de>
    Signed-off-by: Matthias Koenig <mkoenig@suse.de>
    Signed-off-by: Karel Zak <kzak@redhat.com>

Index: util-linux-ng-2.13.1/mount/lomount.c
===================================================================
--- util-linux-ng-2.13.1.orig/mount/lomount.c
+++ util-linux-ng-2.13.1/mount/lomount.c
@@ -143,7 +143,7 @@ show_used_loop_devices (void) {
 
 	for (j = 0; j < SIZE(loop_formats); j++) {
 	    for(i = 0; i < 256; i++) {
-		sprintf(dev, loop_formats[j], i);
+		snprintf(dev, sizeof(dev), loop_formats[j], i);
 		if (stat (dev, &statbuf) == 0 && S_ISBLK(statbuf.st_mode)) {
 			fd = open (dev, O_RDONLY);
 			if (fd >= 0) {
@@ -169,6 +169,102 @@ show_used_loop_devices (void) {
 
 #endif
 
+/* check if the loopfile is already associated with the same given
+ * parameters.
+ *
+ * returns: -1 error
+ *           0 unused
+ *           1 loop device already used
+ */
+static int
+is_associated(int dev, struct stat *file, unsigned long long offset)
+{
+	struct loop_info64 linfo64;
+	struct loop_info64 linfo;
+	int ret = 0;
+
+	if (ioctl(dev, LOOP_GET_STATUS64, &linfo64) == 0) {
+		if (file->st_dev == linfo64.lo_device &&
+	            file->st_ino == linfo64.lo_inode &&
+		    offset == linfo64.lo_offset)
+			ret = 1;
+		return ret;
+	}
+	if (ioctl(dev, LOOP_GET_STATUS, &linfo) == 0) {
+		if (file->st_dev == linfo.lo_device &&
+	            file->st_ino == linfo.lo_inode &&
+		    offset == linfo.lo_offset)
+			ret = 1;
+		return ret;
+	}
+
+	return errno == ENXIO ? 0 : -1;
+}
+
+/* check if the loop file is already used with the same given
+ * parameters. We check for device no, inode and offset.
+ * returns: associated devname or NULL
+ */
+char *
+loopfile_used (const char *filename, unsigned long long offset) {
+	char dev[20];
+	char *loop_formats[] = { "/dev/loop%d", "/dev/loop/%d" };
+	int i, j, fd;
+	struct stat devstat, filestat;
+	struct loop_info loopinfo;
+
+	if (stat(filename, &filestat) == -1) {
+		perror(filename);
+		return NULL;
+	}
+
+	for (j = 0; j < SIZE(loop_formats); j++) {
+	    for(i = 0; i < 256; i++) {
+		snprintf(dev, sizeof(dev), loop_formats[j], i);
+		if (stat (dev, &devstat) == 0 && S_ISBLK(devstat.st_mode)) {
+			fd = open (dev, O_RDONLY);
+			if (fd >= 0) {
+				int res = 0;
+
+				if(ioctl (fd, LOOP_GET_STATUS, &loopinfo) == 0)
+					res = is_associated(fd, &filestat, offset);
+				close (fd);
+				if (res == 1)
+					return xstrdup(dev);
+			}
+			continue; /* continue trying as long as devices exist */
+		}
+		break;
+	    }
+	}
+	return NULL;
+}
+
+int
+loopfile_used_with(char *devname, const char *filename, unsigned long long offset)
+{
+	struct stat statbuf;
+	int fd, ret;
+
+	if (!is_loop_device(devname))
+		return 0;
+
+	if (stat(filename, &statbuf) == -1) {
+		perror(filename);
+		return -1;
+	}
+
+	fd = open(devname, O_RDONLY);
+	if (fd == -1) {
+		perror(devname);
+		return -1;
+	}
+	ret = is_associated(fd, &statbuf, offset);
+
+	close(fd);
+	return ret;
+}
+
 int
 is_loop_device (const char *device) {
 	struct stat statbuf;
@@ -284,6 +380,16 @@ set_loop(const char *device, const char 
 	char *filename;
 	char res_file[PATH_MAX+1];
 
+	if (verbose) {
+		char *xdev = loopfile_used(file, offset);
+
+		if (xdev) {
+			printf(_("warning: %s is already associated with %s\n"),
+					file, xdev);
+			free(xdev);
+		}
+	}
+
 	mode = (*loopro ? O_RDONLY : O_RDWR);
 	if ((ffd = open(file, mode)) < 0) {
 		if (!*loopro && errno == EROFS)
Index: util-linux-ng-2.13.1/mount/lomount.h
===================================================================
--- util-linux-ng-2.13.1.orig/mount/lomount.h
+++ util-linux-ng-2.13.1/mount/lomount.h
@@ -4,3 +4,6 @@ extern int set_loop(const char *, const 
 extern int del_loop(const char *);
 extern int is_loop_device(const char *);
 extern char * find_unused_loop_device(void);
+
+extern int loopfile_used_with(char *devname, const char *filename, unsigned long long offset);
+extern char *loopfile_used (const char *filename, unsigned long long offset);
Index: util-linux-ng-2.13.1/mount/mount.c
===================================================================
--- util-linux-ng-2.13.1.orig/mount/mount.c
+++ util-linux-ng-2.13.1/mount/mount.c
@@ -42,6 +42,7 @@
 #include "mount_paths.h"
 #include "env.h"
 #include "nls.h"
+#include "realpath.h"
 
 #define DO_PS_FIDDLING
 
@@ -833,9 +834,49 @@ suid_check(const char *spec, const char 
   *flags &= ~(MS_OWNER | MS_GROUP);
 }
 
+/* Check, if there already exists a mounted loop device on the mountpoint node
+ * with the same parameters.
+ */
+static int
+is_mounted_same_loopfile(const char *node0, const char *loopfile, unsigned long long offset)
+{
+	struct mntentchn *mnt = NULL;
+	char node[PATH_MAX+1];
+	int res = 0;
+
+	myrealpath(node0, node, PATH_MAX);
+
+	/* Search for mountpoint node in mtab,
+	 * procceed if any of these has the loop option set or
+	 * the device is a loop device
+	 */
+	mnt = getmntdirbackward(node, mnt);
+	if (!mnt) {
+		return 0;
+	}
+	for(; mnt && res == 0; mnt = getmntdirbackward(node, mnt)) {
+		char *p;
+
+		if (strncmp(mnt->m.mnt_fsname, "/dev/loop", 9) == 0)
+			res = loopfile_used_with((char *) mnt->m.mnt_fsname,
+					loopfile, offset);
+
+		else if ((p = strstr(mnt->m.mnt_opts, "loop="))) {
+			char *dev = xstrdup(p+5);
+			if ((p = strchr(dev, ',')))
+				*p = '\0';
+			res = loopfile_used_with(dev, loopfile, offset);
+			free(dev);
+		}
+	}
+
+	return res;
+}
+
 static int
 loop_check(const char **spec, const char **type, int *flags,
-	   int *loop, const char **loopdev, const char **loopfile) {
+	   int *loop, const char **loopdev, const char **loopfile,
+	   const char *node) {
   int looptype;
   unsigned long long offset;
 
@@ -876,6 +917,11 @@ loop_check(const char **spec, const char
 
       offset = opt_offset ? strtoull(opt_offset, NULL, 0) : 0;
 
+      if (is_mounted_same_loopfile(node, *loopfile, offset)) {
+        error(_("mount: according to mtab %s is already mounted on %s as loop"), *loopfile, node);
+        return EX_FAIL;
+      }
+
       do {
         if (!*loopdev || !**loopdev)
 	  *loopdev = find_unused_loop_device();
@@ -1061,7 +1107,7 @@ try_mount_one (const char *spec0, const 
        * stale assignments of files to loop devices. Nasty when used for
        * encryption.
        */
-      res = loop_check(&spec, &types, &flags, &loop, &loopdev, &loopfile);
+      res = loop_check(&spec, &types, &flags, &loop, &loopdev, &loopfile, node);
       if (res)
 	  goto out;
   }