[patch 3/3] vfs: fix sys_getcwd for detached mounts

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

Currently getcwd(2) on a detached mount will give a garbled result:

   > mkdir /mnt/foo
   > mount --bind /etc /mnt/foo
   > cd /mnt/foo/skel
   > /bin/pwd
   /mnt/foo/skel
   > umount -l /mnt/foo
   > /bin/pwd
   etcskel

After the patch it will give "detached:skel" as result.

Thanks to John Johansen for pointing out this bug.

Comment from Al Viro: use "detached:" prefix to differentiate it from
attached paths.

Reported-by: John Johansen <jjohansen@xxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 fs/dcache.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c	2008-06-23 17:35:39.000000000 +0200
+++ linux-2.6/fs/dcache.c	2008-06-23 17:46:05.000000000 +0200
@@ -1828,8 +1828,16 @@ char *__d_path(const struct path *path, 
 
 global_root:
 	retval += 1;	/* hit the slash */
-	if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
-		goto Elong;
+
+	if (IS_ROOT(dentry)) {
+		/* Attached, or pseudo filesystem with "foo:" prefix */
+		if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
+			goto Elong;
+	} else {
+		/* Detached */
+		if (prepend(&retval, &buflen, "detached:", 9) != 0)
+			goto Elong;
+	}
 	root->mnt = vfsmnt;
 	root->dentry = dentry;
 	return retval;

--
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