[PATCH 4.6 041/203] autofs braino fix for do_last()

Greg Kroah-Hartman
2016-07-25T22:25:53Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit e6ec03a25f12b312b7e0c037fe4a6471c4ee5665 upstream.

It's an analogue of commit 7500c38a (fix the braino in "namei:
massage lookup_slow() to be usable by lookup_one_len_unlocked()").
The same problem (->lookup()-returned unhashed negative dentry
just might be an autofs one with ->d_manage() that would wait
until the daemon makes it positive) applies in do_last() - we
need to do follow_managed() first.

Fortunately, remaining callers of follow_managed() are OK - only
autofs has that weirdness (negative dentry that does not mean
an instant -ENOENT)) and autofs never has its negative dentries
hashed, so we can't pick one from a dcache lookup.

->d_manage() is a bloody mess ;-/

Spotted-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/namei.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3173,6 +3173,10 @@ retry_lookup:
got_write = false;
}

+ error = follow_managed(&path, nd);
+ if (unlikely(error < 0))
+ return error;
+
if (unlikely(d_is_negative(path.dentry))) {
path_to_nameidata(&path, nd);
return -ENOENT;
@@ -3188,10 +3192,6 @@ retry_lookup:
return -EEXIST;
}

- error = follow_managed(&path, nd);
- if (unlikely(error < 0))
- return error;
-
seq = 0; /* out of RCU mode, so the value doesn't matter */
inode = d_backing_inode(path.dentry);