[PATCH 1/3] libmount: fix mount -oloop=/dev/loopX regression

[PATCH 1/3] libmount: fix mount -oloop=/dev/loopX regression

[Stanislav Brabec]

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>
---
 libmount/src/context_loopdev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libmount/src/context_loopdev.c b/libmount/src/context_loopdev.c
index 8ef183107..18eb2cc56 100644
--- 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;
-- 
2.11.0

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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