umount: do not hang with disconnected NFS mounts

Since util-linux commit f4612577c942a3683b97632ad0b49671897c2070,
umount stat(2)s its argument to check whether it can be associated
with some loop device. This could hang with broken NFS mounts.

Fix by first checking mtab if umount's argument is mounted and only if
we fail, check if there is a loop device associated.

http://marc.info/?l=util-linux-ng&m=130924963804836&w=2

Reported-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Petr Uzel <petr.uzel@suse.cz>

1 files changed, 22 insertions, 20 deletions

diff --git a/mount/umount.c b/mount/umount.c
index 0349cb3fc..96c940e21 100644
--- a/mount/umount.c
+++ b/mount/umount.c
@@ -600,6 +600,7 @@ umount_file (char *arg) {
 	int fstab_has_user, fstab_has_users, fstab_has_owner, fstab_has_group;
 	int ok, status = 0;
 	struct stat statbuf;
+	char *loopdev = NULL;
 
 	if (!*arg) {		/* "" would be expanded to `pwd` */
 		die(2, _("Cannot unmount \"\"\n"));
@@ -608,26 +609,7 @@ umount_file (char *arg) {
 
 	file = canonicalize(arg); /* mtab paths are canonicalized */
 
-	/* if file is a regular file, check if it is associated
-	 * with some loop device
-	 */
-	if (!stat(file, &statbuf) && S_ISREG(statbuf.st_mode)) {
-		char *loopdev = NULL;
-		switch (find_loopdev_by_backing_file(file, &loopdev)) {
-		case 0:
-			if (verbose)
-				printf(_("%s is associated with %s, trying to unmount it\n"),
-				       arg, loopdev);
-			file = loopdev;
-			break;
-		case 2:
-			if (verbose)
-				printf(_("%s is associated with more than one loop device: not unmounting\n"),
-				       arg);
-			break;
-		}
-	}
-
+try_loopdev:
 	if (verbose > 1)
 		printf(_("Trying to unmount %s\n"), file);
 
@@ -659,6 +641,26 @@ umount_file (char *arg) {
 	if (!mc && verbose)
 		printf(_("Could not find %s in mtab\n"), file);
 
+	/* not found in mtab - check if it is associated with some loop device
+	 * (only if it is a regular file)
+	 */
+	if (!mc && !loopdev && !stat(file, &statbuf) && S_ISREG(statbuf.st_mode)) {
+		switch (find_loopdev_by_backing_file(file, &loopdev)) {
+		case 0:
+			if (verbose)
+				printf(_("%s is associated with %s\n"),
+				       arg, loopdev);
+			file = loopdev;
+			goto try_loopdev;
+			break;
+		case 2:
+			if (verbose)
+				printf(_("%s is associated with more than one loop device: not unmounting\n"),
+				       arg);
+			break;
+		}
+	}
+
 	if (mc) {
 		/*
 		 * helper - umount helper (e.g. pam_mount)