linux-kernel - Re: [PATCH] VFS: Add back check for !inode in walk

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Date:	Thu, 7 May 2015 22:47:55 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] VFS: Add back check for !inode in walk_component()

On Thu, May 07, 2015 at 03:33:21PM -0400, Steven Rostedt wrote:
> On Thu, 7 May 2015 19:43:43 +0100
> Al Viro <viro@...IV.linux.org.uk> wrote:
> 
> 
> > Actually, could you try the following on top of -rc2?
> 
> Gives me the following on boot up:

Gah...  Sorry, I'm an idiot - *path is left uninitialized in that
case.  Fixed.  Could you see if that works?

diff --git a/fs/namei.c b/fs/namei.c
index 4a8d998b..2c8b94e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1415,6 +1415,7 @@ static int lookup_fast(struct nameidata *nd,
 	 */
 	if (nd->flags & LOOKUP_RCU) {
 		unsigned seq;
+		bool negative;
 		dentry = __d_lookup_rcu(parent, &nd->last, &seq);
 		if (!dentry)
 			goto unlazy;
@@ -1424,8 +1425,11 @@ static int lookup_fast(struct nameidata *nd,
 		 * the dentry name information from lookup.
 		 */
 		*inode = dentry->d_inode;
+		negative = d_is_negative(dentry);
 		if (read_seqcount_retry(&dentry->d_seq, seq))
 			return -ECHILD;
+		if (negative)
+			return -ENOENT;
 
 		/*
 		 * This sequence count validates that the parent had no
@@ -1472,6 +1476,10 @@ unlazy:
 		goto need_lookup;
 	}
 
+	if (unlikely(d_is_negative(dentry))) {
+		dput(dentry);
+		return -ENOENT;
+	} 
 	path->mnt = mnt;
 	path->dentry = dentry;
 	err = follow_managed(path, nd->flags);
@@ -1583,10 +1591,10 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
 			goto out_err;
 
 		inode = path->dentry->d_inode;
+		err = -ENOENT;
+		if (d_is_negative(path->dentry))
+			goto out_path_put;
 	}
-	err = -ENOENT;
-	if (d_is_negative(path->dentry))
-		goto out_path_put;
 
 	if (should_follow_link(path->dentry, follow)) {
 		if (nd->flags & LOOKUP_RCU) {
@@ -3036,14 +3044,13 @@ retry_lookup:
 
 	BUG_ON(nd->flags & LOOKUP_RCU);
 	inode = path->dentry->d_inode;
-finish_lookup:
-	/* we _can_ be in RCU mode here */
 	error = -ENOENT;
 	if (d_is_negative(path->dentry)) {
 		path_to_nameidata(path, nd);
 		goto out;
 	}
-
+finish_lookup:
+	/* we _can_ be in RCU mode here */
 	if (should_follow_link(path->dentry, !symlink_ok)) {
 		if (nd->flags & LOOKUP_RCU) {
 			if (unlikely(nd->path.mnt != path->mnt ||
--
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