libmount: fix mount -oloop=/dev/loopX regression

If mount option "loop" is used with an argument, it should be respected. Commit
8efad715 introduced a regression. Even with an argument, overlaying loop device
is searched and argument is ignored. It could have unexpected side effects.

If argument is set, never allocate a new loop device.

How to reproduce:
mkdir -p cdrom
mkisofs -o cdrom.iso cdrom/ 2>/dev/null
losetup /dev/loop0 cdrom.iso
strace mount -t auto -o ro,loop=/dev/loop1 cdrom.iso /mnt 2>&1 | grep ^mount
cat /proc/self/mountinfo | grep /mnt
umount /mnt
losetup -d /dev/loop0

mount("/dev/loop0", "/mnt", "iso9660", MS_MGC_VAL|MS_RDONLY, NULL) = 0
327 60 7:0 / /mnt ro,relatime shared:241 - iso9660 /dev/loop0 ro
losetup: /dev/loop0: detach failed: No such device or address

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>

diff --git a/libmount/src/context_loopdev.c b/libmount/src/context_loopdev.c
index 8ef183107e2b9e7cd686efdcba0efd28dc602ba3..18eb2cc56c760269541752150544f6572c7494bf 100644 (file)
--- a/libmount/src/context_loopdev.c
+++ b/libmount/src/context_loopdev.c
@@ -259,7 +259,12 @@ int mnt_context_setup_loopdev(struct libmnt_context *cxt)
                                goto done;
                        }
                        rc = 0;
-                       goto success;
+                       /* loop= used with argument. Conflict will occur. */
+                       if (loopval) {
+                               rc = -MNT_ERR_LOOPOVERLAP;
+                               goto done;
+                       } else
+                               goto success;
                }
                default: /* error */
                        goto done;