cifs: allocate buffer in the caller of build_path_from_dentry()

build_path_from_dentry() open-codes dentry_path_raw().  The reason
we can't use dentry_path_raw() in there (and postprocess the
result as needed) is that the callers of build_path_from_dentry()
expect that the object to be freed on cleanup and the string to
be used are at the same address.  That's painful, since the path
is naturally built end-to-beginning - we start at the leaf and
go through the ancestors, accumulating the pathname.

Life would be easier if we left the buffer allocation to callers.
It wouldn't be exact-sized buffer, but none of the callers keep
the result for long - it's always freed before the caller returns.
So there's no need to do exact-sized allocation; better use
__getname()/__putname(), same as we do for pathname arguments
of syscalls.  What's more, there's no need to do allocation under
spinlocks, so GFP_ATOMIC is not needed.

Next patch will replace the open-coded dentry_path_raw() (in
build_path_from_dentry_optional_prefix()) with calling the real
thing.  This patch only introduces wrappers for allocating/freeing
the buffers and switches to new calling conventions:
	build_path_from_dentry(dentry, buf)
expects buf to be address of a page-sized object or NULL,
return value is a pathname built inside that buffer on success,
ERR_PTR(-ENOMEM) if buf is NULL and ERR_PTR(-ENAMETOOLONG) if
the pathname won't fit into page.  Note that we don't need to
check for failure when allocating the buffer in the caller -
build_path_from_dentry() will do the right thing.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 53 insertions, 51 deletions

diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index 0b29893f40b7..fe3a50a39f41 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -1609,7 +1609,8 @@ int cifs_unlink(struct inode *dir, struct dentry *dentry)
 {
 	int rc = 0;
 	unsigned int xid;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page;
 	struct inode *inode = d_inode(dentry);
 	struct cifsInodeInfo *cifs_inode;
 	struct super_block *sb = dir->i_sb;
@@ -1629,6 +1630,7 @@ int cifs_unlink(struct inode *dir, struct dentry *dentry)
 	server = tcon->ses->server;
 
 	xid = get_xid();
+	page = alloc_dentry_path();
 
 	if (tcon->nodelete) {
 		rc = -EACCES;
@@ -1637,9 +1639,9 @@ int cifs_unlink(struct inode *dir, struct dentry *dentry)
 
 	/* Unlink can be called from rename so we can not take the
 	 * sb->s_vfs_rename_mutex here */
-	full_path = build_path_from_dentry(dentry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(dentry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto unlink_out;
 	}
 
@@ -1713,7 +1715,7 @@ out_reval:
 	cifs_inode = CIFS_I(dir);
 	CIFS_I(dir)->time = 0;	/* force revalidate of dir as well */
 unlink_out:
-	kfree(full_path);
+	free_dentry_path(page);
 	kfree(attrs);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
@@ -1867,6 +1869,7 @@ int cifs_mkdir(struct user_namespace *mnt_userns, struct inode *inode,
 	struct cifs_tcon *tcon;
 	struct TCP_Server_Info *server;
 	const char *full_path;
+	void *page;
 
 	cifs_dbg(FYI, "In cifs_mkdir, mode = %04ho inode = 0x%p\n",
 		 mode, inode);
@@ -1879,9 +1882,10 @@ int cifs_mkdir(struct user_namespace *mnt_userns, struct inode *inode,
 
 	xid = get_xid();
 
-	full_path = build_path_from_dentry(direntry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	page = alloc_dentry_path();
+	full_path = build_path_from_dentry(direntry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto mkdir_out;
 	}
 
@@ -1924,7 +1928,7 @@ mkdir_out:
 	 * attributes are invalid now.
 	 */
 	CIFS_I(inode)->time = 0;
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;
@@ -1938,16 +1942,17 @@ int cifs_rmdir(struct inode *inode, struct dentry *direntry)
 	struct tcon_link *tlink;
 	struct cifs_tcon *tcon;
 	struct TCP_Server_Info *server;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page = alloc_dentry_path();
 	struct cifsInodeInfo *cifsInode;
 
 	cifs_dbg(FYI, "cifs_rmdir, inode = 0x%p\n", inode);
 
 	xid = get_xid();
 
-	full_path = build_path_from_dentry(direntry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(direntry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto rmdir_exit;
 	}
 
@@ -1997,7 +2002,7 @@ int cifs_rmdir(struct inode *inode, struct dentry *direntry)
 		current_time(inode);
 
 rmdir_exit:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	return rc;
 }
@@ -2072,8 +2077,8 @@ cifs_rename2(struct user_namespace *mnt_userns, struct inode *source_dir,
 	     struct dentry *source_dentry, struct inode *target_dir,
 	     struct dentry *target_dentry, unsigned int flags)
 {
-	const char *from_name = NULL;
-	const char *to_name = NULL;
+	const char *from_name, *to_name;
+	void *page1, *page2;
 	struct cifs_sb_info *cifs_sb;
 	struct tcon_link *tlink;
 	struct cifs_tcon *tcon;
@@ -2091,21 +2096,19 @@ cifs_rename2(struct user_namespace *mnt_userns, struct inode *source_dir,
 		return PTR_ERR(tlink);
 	tcon = tlink_tcon(tlink);
 
+	page1 = alloc_dentry_path();
+	page2 = alloc_dentry_path();
 	xid = get_xid();
 
-	/*
-	 * we already have the rename sem so we do not need to
-	 * grab it again here to protect the path integrity
-	 */
-	from_name = build_path_from_dentry(source_dentry);
-	if (from_name == NULL) {
-		rc = -ENOMEM;
+	from_name = build_path_from_dentry(source_dentry, page1);
+	if (IS_ERR(from_name)) {
+		rc = PTR_ERR(from_name);
 		goto cifs_rename_exit;
 	}
 
-	to_name = build_path_from_dentry(target_dentry);
-	if (to_name == NULL) {
-		rc = -ENOMEM;
+	to_name = build_path_from_dentry(target_dentry, page2);
+	if (IS_ERR(to_name)) {
+		rc = PTR_ERR(to_name);
 		goto cifs_rename_exit;
 	}
 
@@ -2177,8 +2180,8 @@ unlink_target:
 
 cifs_rename_exit:
 	kfree(info_buf_source);
-	kfree(from_name);
-	kfree(to_name);
+	free_dentry_path(page2);
+	free_dentry_path(page1);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
 	return rc;
@@ -2317,7 +2320,8 @@ int cifs_revalidate_dentry_attr(struct dentry *dentry)
 	int rc = 0;
 	struct inode *inode = d_inode(dentry);
 	struct super_block *sb = dentry->d_sb;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page;
 	int count = 0;
 
 	if (inode == NULL)
@@ -2328,11 +2332,10 @@ int cifs_revalidate_dentry_attr(struct dentry *dentry)
 
 	xid = get_xid();
 
-	/* can not safely grab the rename sem here if rename calls revalidate
-	   since that would deadlock */
-	full_path = build_path_from_dentry(dentry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	page = alloc_dentry_path();
+	full_path = build_path_from_dentry(dentry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto out;
 	}
 
@@ -2351,7 +2354,7 @@ again:
 	if (rc == -EAGAIN && count++ < 10)
 		goto again;
 out:
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 
 	return rc;
@@ -2613,7 +2616,8 @@ cifs_setattr_unix(struct dentry *direntry, struct iattr *attrs)
 {
 	int rc;
 	unsigned int xid;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page = alloc_dentry_path();
 	struct inode *inode = d_inode(direntry);
 	struct cifsInodeInfo *cifsInode = CIFS_I(inode);
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
@@ -2634,9 +2638,9 @@ cifs_setattr_unix(struct dentry *direntry, struct iattr *attrs)
 	if (rc < 0)
 		goto out;
 
-	full_path = build_path_from_dentry(direntry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
+	full_path = build_path_from_dentry(direntry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
 		goto out;
 	}
 
@@ -2748,7 +2752,7 @@ cifs_setattr_unix(struct dentry *direntry, struct iattr *attrs)
 		cifsInode->time = 0;
 out:
 	kfree(args);
-	kfree(full_path);
+	free_dentry_path(page);
 	free_xid(xid);
 	return rc;
 }
@@ -2764,7 +2768,8 @@ cifs_setattr_nounix(struct dentry *direntry, struct iattr *attrs)
 	struct cifsInodeInfo *cifsInode = CIFS_I(inode);
 	struct cifsFileInfo *wfile;
 	struct cifs_tcon *tcon;
-	const char *full_path = NULL;
+	const char *full_path;
+	void *page = alloc_dentry_path();
 	int rc = -EACCES;
 	__u32 dosattr = 0;
 	__u64 mode = NO_CHANGE_64;
@@ -2778,16 +2783,13 @@ cifs_setattr_nounix(struct dentry *direntry, struct iattr *attrs)
 		attrs->ia_valid |= ATTR_FORCE;
 
 	rc = setattr_prepare(&init_user_ns, direntry, attrs);
-	if (rc < 0) {
-		free_xid(xid);
-		return rc;
-	}
+	if (rc < 0)
+		goto cifs_setattr_exit;
 
-	full_path = build_path_from_dentry(direntry);
-	if (full_path == NULL) {
-		rc = -ENOMEM;
-		free_xid(xid);
-		return rc;
+	full_path = build_path_from_dentry(direntry, page);
+	if (IS_ERR(full_path)) {
+		rc = PTR_ERR(full_path);
+		goto cifs_setattr_exit;
 	}
 
 	/*
@@ -2937,8 +2939,8 @@ cifs_setattr_nounix(struct dentry *direntry, struct iattr *attrs)
 	mark_inode_dirty(inode);
 
 cifs_setattr_exit:
-	kfree(full_path);
 	free_xid(xid);
+	free_dentry_path(page);
 	return rc;
 }