ext4: optimize ea_inode block expansion

Copy ea data from inode entry when expanding ea block if possible.
Then remove the ea entry if expansion success. Thus memcpy to a
temporary buffer may be avoided.

If the expansion fails, we do not need to recovery the removed ea
entry neither in this way.

Reported-by: syzbot+2dacb8f015bf1420155f@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=3613786cb88c93aa1c6a279b1df6a7b201347d08
Link: https://lore.kernel.org/r/20230103014517.495275-2-jun.nie@linaro.org
Cc: stable@kernel.org
Signed-off-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/xattr.c

@@ -2600,9 +2600,8 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 
 	is = kzalloc(sizeof(struct ext4_xattr_ibody_find), GFP_NOFS);
 	bs = kzalloc(sizeof(struct ext4_xattr_block_find), GFP_NOFS);
-	buffer = kvmalloc(value_size, GFP_NOFS);
 	b_entry_name = kmalloc(entry->e_name_len + 1, GFP_NOFS);
-	if (!is || !bs || !buffer || !b_entry_name) {
+	if (!is || !bs || !b_entry_name) {
 		error = -ENOMEM;
 		goto out;
 	}
@@ -2614,12 +2613,18 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 
 	/* Save the entry name and the entry value */
 	if (entry->e_value_inum) {
+		buffer = kvmalloc(value_size, GFP_NOFS);
+		if (!buffer) {
+			error = -ENOMEM;
+			goto out;
+		}
+
 		error = ext4_xattr_inode_get(inode, entry, buffer, value_size);
 		if (error)
 			goto out;
 	} else {
 		size_t value_offs = le16_to_cpu(entry->e_value_offs);
-		memcpy(buffer, (void *)IFIRST(header) + value_offs, value_size);
+		buffer = (void *)IFIRST(header) + value_offs;
 	}
 
 	memcpy(b_entry_name, entry->e_name, entry->e_name_len);
@@ -2634,25 +2639,26 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 	if (error)
 		goto out;
 
-	/* Remove the chosen entry from the inode */
-	error = ext4_xattr_ibody_set(handle, inode, &i, is);
-	if (error)
-		goto out;
-
 	i.value = buffer;
 	i.value_len = value_size;
 	error = ext4_xattr_block_find(inode, &i, bs);
 	if (error)
 		goto out;
 
-	/* Add entry which was removed from the inode into the block */
+	/* Move ea entry from the inode into the block */
 	error = ext4_xattr_block_set(handle, inode, &i, bs);
 	if (error)
 		goto out;
-	error = 0;
+
+	/* Remove the chosen entry from the inode */
+	i.value = NULL;
+	i.value_len = 0;
+	error = ext4_xattr_ibody_set(handle, inode, &i, is);
+
 out:
 	kfree(b_entry_name);
-	kvfree(buffer);
+	if (entry->e_value_inum && buffer)
+		kvfree(buffer);
 	if (is)
 		brelse(is->iloc.bh);
 	if (bs)