Re: [Qemu-devel] [V9fs-developer] [Bug 1336794] Re: 9pfs does not honor open file handles on unlinked files

[Al Viro <viro@ZenIV.linux.org.uk>]

On Tue, Apr 14, 2015 at 04:19:41PM +0000, Eric Van Hensbergen wrote:
> That patch looks fine by me.  Happy to put it in the queue.  Thanks Al.

	OK...  Here's one more:

9p: don't bother with __getname() in ->follow_link()

We copy there a kmalloc'ed string and proceed to kfree that string immediately
after that.  Easier to just feed that string to nd_set_link() and _not_
kfree it until ->put_link() (which becomes kfree_put_link() in that case).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index 099c771..48d35d8 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -150,8 +150,6 @@ extern int v9fs_vfs_unlink(struct inode *i, struct dentry *d);
 extern int v9fs_vfs_rmdir(struct inode *i, struct dentry *d);
 extern int v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 			struct inode *new_dir, struct dentry *new_dentry);
-extern void v9fs_vfs_put_link(struct dentry *dentry, struct nameidata *nd,
-			void *p);
 extern struct inode *v9fs_inode_from_fid(struct v9fs_session_info *v9ses,
 					 struct p9_fid *fid,
 					 struct super_block *sb, int new);
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index cda68f7..0ba1171 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -1224,103 +1224,46 @@ ino_t v9fs_qid2ino(struct p9_qid *qid)
 }
 
 /**
- * v9fs_readlink - read a symlink's location (internal version)
+ * v9fs_vfs_follow_link - follow a symlink path
  * @dentry: dentry for symlink
- * @buffer: buffer to load symlink location into
- * @buflen: length of buffer
+ * @nd: nameidata
  *
  */
 
-static int v9fs_readlink(struct dentry *dentry, char *buffer, int buflen)
+static void *v9fs_vfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
-	int retval;
-
-	struct v9fs_session_info *v9ses;
-	struct p9_fid *fid;
+	struct v9fs_session_info *v9ses = v9fs_dentry2v9ses(dentry);
+	struct p9_fid *fid = v9fs_fid_lookup(dentry);
 	struct p9_wstat *st;
 
-	p9_debug(P9_DEBUG_VFS, " %pd\n", dentry);
-	retval = -EPERM;
-	v9ses = v9fs_dentry2v9ses(dentry);
-	fid = v9fs_fid_lookup(dentry);
+	p9_debug(P9_DEBUG_VFS, "%pd\n", dentry);
+
 	if (IS_ERR(fid))
-		return PTR_ERR(fid);
+		return ERR_CAST(fid);
 
 	if (!v9fs_proto_dotu(v9ses))
-		return -EBADF;
+		return ERR_PTR(-EBADF);
 
 	st = p9_client_stat(fid);
 	if (IS_ERR(st))
-		return PTR_ERR(st);
+		return ERR_CAST(st);
 
 	if (!(st->mode & P9_DMSYMLINK)) {
-		retval = -EINVAL;
-		goto done;
+		p9stat_free(st);
+		kfree(st);
+		return ERR_PTR(-EINVAL);
 	}
+	if (strlen(st->extension) >= PATH_MAX)
+		st->extension[PATH_MAX - 1] = '\0';
 
-	/* copy extension buffer into buffer */
-	retval = min(strlen(st->extension)+1, (size_t)buflen);
-	memcpy(buffer, st->extension, retval);
-
-	p9_debug(P9_DEBUG_VFS, "%pd -> %s (%.*s)\n",
-		 dentry, st->extension, buflen, buffer);
-
-done:
+	nd_set_link(nd, st->extension);
+	st->extension = NULL;
 	p9stat_free(st);
 	kfree(st);
-	return retval;
-}
-
-/**
- * v9fs_vfs_follow_link - follow a symlink path
- * @dentry: dentry for symlink
- * @nd: nameidata
- *
- */
-
-static void *v9fs_vfs_follow_link(struct dentry *dentry, struct nameidata *nd)
-{
-	int len = 0;
-	char *link = __getname();
-
-	p9_debug(P9_DEBUG_VFS, "%pd\n", dentry);
-
-	if (!link)
-		link = ERR_PTR(-ENOMEM);
-	else {
-		len = v9fs_readlink(dentry, link, PATH_MAX);
-
-		if (len < 0) {
-			__putname(link);
-			link = ERR_PTR(len);
-		} else
-			link[min(len, PATH_MAX-1)] = 0;
-	}
-	nd_set_link(nd, link);
-
 	return NULL;
 }
 
 /**
- * v9fs_vfs_put_link - release a symlink path
- * @dentry: dentry for symlink
- * @nd: nameidata
- * @p: unused
- *
- */
-
-void
-v9fs_vfs_put_link(struct dentry *dentry, struct nameidata *nd, void *p)
-{
-	char *s = nd_get_link(nd);
-
-	p9_debug(P9_DEBUG_VFS, " %pd %s\n",
-		 dentry, IS_ERR(s) ? "<error>" : s);
-	if (!IS_ERR(s))
-		__putname(s);
-}
-
-/**
  * v9fs_vfs_mkspecial - create a special file
  * @dir: inode to create special file in
  * @dentry: dentry to create
@@ -1514,7 +1457,7 @@ static const struct inode_operations v9fs_file_inode_operations = {
 static const struct inode_operations v9fs_symlink_inode_operations = {
 	.readlink = generic_readlink,
 	.follow_link = v9fs_vfs_follow_link,
-	.put_link = v9fs_vfs_put_link,
+	.put_link = kfree_put_link,
 	.getattr = v9fs_vfs_getattr,
 	.setattr = v9fs_vfs_setattr,
 };
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 9861c7c..bc2a91f 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -912,33 +912,18 @@ error:
 static void *
 v9fs_vfs_follow_link_dotl(struct dentry *dentry, struct nameidata *nd)
 {
-	int retval;
-	struct p9_fid *fid;
-	char *link = __getname();
+	struct p9_fid *fid = v9fs_fid_lookup(dentry);
 	char *target;
+	int retval;
 
 	p9_debug(P9_DEBUG_VFS, "%pd\n", dentry);
 
-	if (!link) {
-		link = ERR_PTR(-ENOMEM);
-		goto ndset;
-	}
-	fid = v9fs_fid_lookup(dentry);
-	if (IS_ERR(fid)) {
-		__putname(link);
-		link = ERR_CAST(fid);
-		goto ndset;
-	}
+	if (IS_ERR(fid))
+		return ERR_CAST(fid);
 	retval = p9_client_readlink(fid, &target);
-	if (!retval) {
-		strcpy(link, target);
-		kfree(target);
-		goto ndset;
-	}
-	__putname(link);
-	link = ERR_PTR(retval);
-ndset:
-	nd_set_link(nd, link);
+	if (retval)
+		return ERR_PTR(retval);
+	nd_set_link(nd, target);
 	return NULL;
 }
 
@@ -1006,7 +991,7 @@ const struct inode_operations v9fs_file_inode_operations_dotl = {
 const struct inode_operations v9fs_symlink_inode_operations_dotl = {
 	.readlink = generic_readlink,
 	.follow_link = v9fs_vfs_follow_link_dotl,
-	.put_link = v9fs_vfs_put_link,
+	.put_link = kfree_put_link,
 	.getattr = v9fs_vfs_getattr_dotl,
 	.setattr = v9fs_vfs_setattr_dotl,
 	.setxattr = generic_setxattr,