linux-kernel - [PATCH 05/16] vfs: make follow

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Date:	Mon, 21 May 2012 17:30:09 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@...radead.org, torvalds@...ux-foundation.org, mszeredi@...e.cz
Subject: [PATCH 05/16] vfs: make follow_link check RCU safe

From: Miklos Szeredi <mszeredi@...e.cz>

This will allow this code to be used in RCU mode.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
---
 fs/namei.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 1dba4a7..67bddd6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2203,6 +2203,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 	int acc_mode = op->acc_mode;
 	struct file *filp;
 	struct inode *inode;
+	int symlink_ok = 0;
 	int error;
 
 	nd->flags &= ~LOOKUP_PARENT;
@@ -2234,7 +2235,6 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 	}
 
 	if (!(open_flag & O_CREAT)) {
-		int symlink_ok = 0;
 		if (nd->last.name[nd->last.len])
 			nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
 		if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW))
@@ -2366,8 +2366,16 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 	if (!inode)
 		goto exit_dput;
 
-	if (inode->i_op->follow_link)
+	if (should_follow_link(inode, !symlink_ok)) {
+		if (nd->flags & LOOKUP_RCU) {
+			if (unlikely(unlazy_walk(nd, path->dentry))) {
+				error = -ECHILD;
+				goto exit;
+			}
+		}
+		BUG_ON(inode != path->dentry->d_inode);
 		return NULL;
+	}
 
 	path_to_nameidata(path, nd);
 	nd->inode = inode;
-- 
1.7.7

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