udf: fix the udf_iget() vs. udf_new_inode() races

Currently udf_iget() (triggered by NFS) can race with udf_new_inode()
leading to two inode structures with the same inode number:

nfsd: iget_locked() creates inode
nfsd: try to read from disk, block on that.
udf_new_inode(): allocate inode with that inumber
udf_new_inode(): insert it into icache, set it up and dirty
udf_write_inode(): write inode into buffer cache
nfsd: get CPU again, look into buffer cache, see nice and sane on-disk
  inode, set the in-core inode from it

Fix the problem by putting inode into icache in locked state (I_NEW set)
and unlocking it only after it's fully set up.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/ialloc.c

@@ -124,7 +124,12 @@ struct inode *udf_new_inode(struct inode *dir, umode_t mode, int *err)
 		iinfo->i_alloc_type = ICBTAG_FLAG_AD_LONG;
 	inode->i_mtime = inode->i_atime = inode->i_ctime =
 		iinfo->i_crtime = current_fs_time(inode->i_sb);
-	insert_inode_hash(inode);
+	if (unlikely(insert_inode_locked(inode) < 0)) {
+		make_bad_inode(inode);
+		iput(inode);
+		*err = -EIO;
+		return NULL;
+	}
 	mark_inode_dirty(inode);
 
 	*err = 0;

fs/udf/namei.c

@@ -559,6 +559,7 @@ static int udf_add_nondir(struct dentry *dentry, struct inode *inode)
 	fi = udf_add_entry(dir, dentry, &fibh, &cfi, &err);
 	if (unlikely(!fi)) {
 		inode_dec_link_count(inode);
+		unlock_new_inode(inode);
 		iput(inode);
 		return err;
 	}
@@ -572,6 +573,7 @@ static int udf_add_nondir(struct dentry *dentry, struct inode *inode)
 	if (fibh.sbh != fibh.ebh)
 		brelse(fibh.ebh);
 	brelse(fibh.sbh);
+	unlock_new_inode(inode);
 	d_instantiate(dentry, inode);
 
 	return 0;
@@ -619,6 +621,7 @@ static int udf_tmpfile(struct inode *dir, struct dentry *dentry, umode_t mode)
 	mark_inode_dirty(inode);
 
 	d_tmpfile(dentry, inode);
+	unlock_new_inode(inode);
 	return 0;
 }
 
@@ -660,6 +663,7 @@ static int udf_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	fi = udf_add_entry(inode, NULL, &fibh, &cfi, &err);
 	if (!fi) {
 		inode_dec_link_count(inode);
+		unlock_new_inode(inode);
 		iput(inode);
 		goto out;
 	}
@@ -678,6 +682,7 @@ static int udf_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	if (!fi) {
 		clear_nlink(inode);
 		mark_inode_dirty(inode);
+		unlock_new_inode(inode);
 		iput(inode);
 		goto out;
 	}
@@ -689,6 +694,7 @@ static int udf_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	udf_write_fi(dir, &cfi, fi, &fibh, NULL, NULL);
 	inc_nlink(dir);
 	mark_inode_dirty(dir);
+	unlock_new_inode(inode);
 	d_instantiate(dentry, inode);
 	if (fibh.sbh != fibh.ebh)
 		brelse(fibh.ebh);
@@ -996,6 +1002,7 @@ static int udf_symlink(struct inode *dir, struct dentry *dentry,
 out_no_entry:
 	up_write(&iinfo->i_data_sem);
 	inode_dec_link_count(inode);
+	unlock_new_inode(inode);
 	iput(inode);
 	goto out;
 }