linux-kernel - [PATCH 3.16 237/305] make nfs_atomic_open() call d_drop() on all ->open

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Message-ID: <lsq.1471110171.713372563@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Oleg Drokin" <green@...uxhacker.ru>,
	"Trond Myklebust" <trond.myklebust@...marydata.com>,
	"Anna Schumaker" <Anna.Schumaker@...app.com>,
	"Al Viro" <viro@...iv.linux.org.uk>,
	"Al Viro" <viro@...IV.linux.org.uk>
Subject: [PATCH 3.16 237/305] make nfs_atomic_open() call d_drop() on all
 ->open_context() errors.

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

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: Ben Hutchings <ben@...adent.org.uk>
---
 fs/nfs/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1492,9 +1492,9 @@ int nfs_atomic_open(struct inode *dir, s
 		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: