Commit e6ec03a2 authored Jun 05, 2016 by Al Viro

autofs braino fix for do_last()



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 ;-/

Cc: stable@vger.kernel.org # v4.6
Spotted-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent fac7d191

fs/namei.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -3260,6 +3260,10 @@ static int do_last(struct nameidata *nd,
		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;
		@@ -3275,10 +3279,6 @@ static int do_last(struct nameidata *nd,
		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);
		finish_lookup: