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.
Signed-off-by: Matthias Koenig <mkoenig@xxxxxxx>
---
mount/lomount.c | 45 ++++++++++++++++++++++++++++++++++++++
mount/lomount.h | 2 +
mount/mount.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 110 insertions(+), 2 deletions(-)
diff --git a/mount/lomount.c b/mount/lomount.c
index e039e68..b0c9c6a 100644
--- a/mount/lomount.c
+++ b/mount/lomount.c
@@ -168,6 +168,51 @@ show_used_loop_devices (void) {
#endif
+/* check if the loop device dev is already used with the same given
+ * parameters. We check for device no, inode and offset.
+ * returns: -1 error
+ * 0 unused
+ * 1 loop device already used
+ */
+int
+loop_device_used(const char *dev, const char *name, unsigned long long offset)
+{
+ struct stat statbuf;
+ struct loop_info64 loopinfo;
+ int fd, ret;
+
+ if (!is_loop_device(dev))
+ return 0;
+
+ if (stat(name, &statbuf) == -1) {
+ perror("stat");
+ return -1;
+ }
+
+ fd = open(dev, O_RDONLY);
+ if (fd == -1) {
+ perror("open");
+ return -1;
+ }
+
+ if (ioctl(fd, LOOP_GET_STATUS64, &loopinfo) == -1) {
+ if (errno == ENXIO)
+ ret = 0;
+ else {
+ perror("ioctl");
+ ret = -1;
+ }
+ } else if (statbuf.st_dev == loopinfo.lo_device &&
+ statbuf.st_ino == loopinfo.lo_inode &&
+ offset == loopinfo.lo_offset)
+ ret = 1;
+ else
+ ret = 0;
+
+ close(fd);
+ return ret;
+}
+
int
is_loop_device (const char *device) {
struct stat statbuf;
diff --git a/mount/lomount.h b/mount/lomount.h
index 89695cd..e1cf8c3 100644
--- a/mount/lomount.h
+++ b/mount/lomount.h
@@ -4,3 +4,5 @@ extern int set_loop(const char *, const char *, unsigned long long,
extern int del_loop(const char *);
extern int is_loop_device(const char *);
extern char * find_unused_loop_device(void);
+extern int loop_device_used(const char *, const char *, unsigned long long);
+
diff --git a/mount/mount.c b/mount/mount.c
index 40699f3..25d9166 100644
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -42,6 +42,7 @@
#include "mount_paths.h"
#include "env.h"
#include "nls.h"
+#include "realpath.h"
#define DO_PS_FIDDLING
@@ -824,9 +825,64 @@ suid_check(const char *spec, const char *node, int *flags, char **user) {
*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 *node, const char *loopfile, unsigned long long offset)
+{
+ struct mntentchn *mnt = NULL;
+ char res_node[PATH_MAX+1];
+ int loop_found = 0;
+ char loop_prefix[] = "/dev/loop";
+ char *p, *loop_device = NULL;
+
+ myrealpath(node, res_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(res_node, mnt);
+ if (!mnt)
+ return 0;
+
+ for(; mnt; mnt = getmntdirbackward(res_node, mnt)) {
+ if (p = strstr(mnt->m.mnt_opts, "loop=")) {
+ /* 1. parse loop device from options */
+ loop_device = xstrdup(p+5);
+ p = strchr(loop_device, ',');
+ if (p)
+ p = '\0';
+ } else if (strncmp(mnt->m.mnt_fsname, loop_prefix,
+ strlen(loop_prefix)) == 0) {
+ /* 2. loop device is fsname */
+ loop_device = xstrdup(mnt->m.mnt_fsname);
+ } else {
+ loop_device = NULL;
+ continue;
+ }
+
+ /* check if there is already a loop device with the *same*
+ * parameters (device, inode, offset)
+ */
+ if (loop_device_used(loop_device, loopfile, offset)) {
+ if (loop_device)
+ free(loop_device);
+ return 1;
+ }
+ }
+
+ if (loop_device)
+ free(loop_device);
+
+ return 0;
+}
+
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;
@@ -867,6 +923,11 @@ loop_check(const char **spec, const char **type, int *flags,
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\n"), *loopfile, node);
+ return EX_FAIL;
+ }
+
do {
if (!*loopdev || !**loopdev)
*loopdev = find_unused_loop_device();
@@ -1052,7 +1113,7 @@ try_mount_one (const char *spec0, const char *node0, const char *types0,
* 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;
}
--
1.5.2.4
-
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