Forwarded: [PATCH] ext4: don't append a directory block already mapped in the inode

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Subject: [PATCH] ext4: don't append a directory block already mapped in the inode
Author: adrianox@xxxxxxxxx

#syz test: upstream 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e
---
 fs/ext4/namei.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 3b9740c1c16d..ff6013306b74 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -83,6 +83,25 @@ static struct buffer_head *ext4_append(handle_t *handle,
 	bh = ext4_bread(handle, inode, *block, EXT4_GET_BLOCKS_CREATE);
 	if (IS_ERR(bh))
 		return bh;
+
+	for (map.m_lblk = 0; map.m_lblk < *block; map.m_lblk += map.m_len) {
+		map.m_len = *block - map.m_lblk;
+		err = ext4_map_blocks(NULL, inode, &map, 0);
+		if (err < 0)
+			goto out;
+		if (err == 0) {
+			map.m_len = 1;
+			continue;
+		}
+		if (unlikely(map.m_pblk == bh->b_blocknr)) {
+			EXT4_ERROR_INODE(inode,
+					 "new block %llu already mapped",
+					 (unsigned long long)bh->b_blocknr);
+			err = -EFSCORRUPTED;
+			goto out;
+		}
+	}
+
 	inode->i_size += inode->i_sb->s_blocksize;
 	EXT4_I(inode)->i_disksize = inode->i_size;
 	err = ext4_mark_inode_dirty(handle, inode);
-- 
2.51.0