I'm not convinced that this is really a safe thing to do: it will
modify the behavior of sys_getcwd() even for the cases when it gave a
somewhat sane (though arguably wrong) result.
So I think it should wait till 2.6.28 as there doesn't seem to be
anybody who is actually bothered by this bug...
Thanks,
Miklos
----
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>
---
fs/dcache.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c 2008-07-30 13:41:50.000000000 +0200
+++ linux-2.6/fs/dcache.c 2008-07-30 13:41:52.000000000 +0200
@@ -1788,6 +1788,12 @@ 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
@@ -1854,8 +1860,16 @@ 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/outside root/outside namespace) */
+ if (prepend(&retval, &buflen, "(unreachable)/", 14) != 0)
+ goto Elong;
+ }
root->mnt = vfsmnt;
root->dentry = dentry;
goto out;
--
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