From: Miklos Szeredi <mszeredi@xxxxxxx>
John Johansen pointed out, that getcwd(2) will give a garbled result if a
bind mount of a non-filesystem-root directory is detached:
> mkdir /mnt/foo
> mount --bind /etc /mnt/foo
> cd /mnt/foo/skel
> umount -l /mnt/foo
> /bin/pwd
etcskel
If it was the root of the filesystem which was detached, it will give a
saner looking result, but it still won't be a valid absolute path by which
the CWD can be reached (assuming the process's root is not also on the
detached mount).
A similar issue happens if the CWD is outside the process's root or in a
different namespace. These problems are relevant to symlinks under
/proc/<pid>/ and /proc/<pid>/fd/ as well.
This patch addresses all these issues, by prefixing such unreachable paths
with "(unreachable)". This isn't perfect since the returned path may
still be a valid _relative_ path, and applications may not check the
result of getcwd() for starting with a '/' before using it.
For this reason Andreas Gruenbacher thinks getcwd(2) should return ENOENT
in these cases, but that breaks /bin/pwd and bash in the above cases.
Reported-by: John Johansen <jjohansen@xxxxxxx>
Cc: Matthew Wilcox <matthew@xxxxxx>
Cc: Andreas Gruenbacher <agruen@xxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Valdis Kletnieks <Valdis.Kletnieks@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dcache.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff -puN fs/dcache.c~vfs-fix-d_path-for-unreachable-paths fs/dcache.c
--- a/fs/dcache.c~vfs-fix-d_path-for-unreachable-paths
+++ a/fs/dcache.c
@@ -1883,6 +1883,12 @@ static int prepend_name(char **buffer, i
return prepend(buffer, buflen, name->name, name->len);
}
+static bool is_pseudo_root(struct dentry *dentry)
+{
+ return IS_ROOT(dentry) &&
+ (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/');
+}
+
/**
* __d_path - return the path of a dentry
* @path: the dentry/vfsmount to report
@@ -1950,8 +1956,18 @@ out:
global_root:
retval += 1; /* hit the slash */
- if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
- goto Elong;
+
+ if (is_pseudo_root(dentry)) {
+ /* Pseudo filesystem with "foo:" prefix */
+ if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
+ goto Elong;
+ } else {
+ /*
+ * Unreachable (detached or outside root or outside namespace)
+ */
+ if (prepend(&retval, &buflen, "(unreachable)/", 14) != 0)
+ goto Elong;
+ }
root->mnt = vfsmnt;
root->dentry = dentry;
goto out;
_
--
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