linux-kernel - [PATCH 3.12 61/88] make nfs_atomic_open() call d_drop() on all ->open

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Message-Id: <edc8ae95e6dc349de1dbec9b1c83dabdf4218669.1468483951.git.jslaby@suse.cz>
Date:	Thu, 14 Jul 2016 10:15:53 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
	Al Viro <viro@...iv.linux.org.uk>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Anna Schumaker <Anna.Schumaker@...app.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 61/88] make nfs_atomic_open() call d_drop() on all ->open_context() errors.

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit d20cb71dbf3487f24549ede1a8e2d67579b4632e upstream.

In "NFSv4: Move dentry instantiation into the NFSv4-specific atomic open code"
unconditional d_drop() after the ->open_context() had been removed.  It had
been correct for success cases (there ->open_context() itself had been doing
dcache manipulations), but not for error ones.  Only one of those (ENOENT)
got a compensatory d_drop() added in that commit, but in fact it should've
been done for all errors.  As it is, the case of O_CREAT non-exclusive open
on a hashed negative dentry racing with e.g. symlink creation from another
client ended up with ->open_context() getting an error and proceeding to
call nfs_lookup().  On a hashed dentry, which would've instantly triggered
BUG_ON() in d_materialise_unique() (or, these days, its equivalent in
d_splice_alias()).

Tested-by: Oleg Drokin <green@...uxhacker.ru>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Trond Myklebust <trond.myklebust@...marydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@...app.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/nfs/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index cf6ede69a2e2..b9670301d7d3 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1483,9 +1483,9 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 		err = PTR_ERR(inode);
 		trace_nfs_atomic_open_exit(dir, ctx, open_flags, err);
 		put_nfs_open_context(ctx);
+		d_drop(dentry);
 		switch (err) {
 		case -ENOENT:
-			d_drop(dentry);
 			d_add(dentry, NULL);
 			break;
 		case -EISDIR:
-- 
2.9.1