ext4: make sure ext4_append() always allocates new block

ext4_append() must always allocate a new block, otherwise we run the
risk of overwriting existing directory block corrupting the directory
tree in the process resulting in all manner of problems later on.

Add a sanity check to see if the logical block is already allocated and
error out if it is.

Cc: stable@kernel.org
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20220704142721.157985-2-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 7fced54e289113e50baa7d23947f61d76278e9eb..3a31b662f6619a57d7f82ce7db16dabdcb449ace 100644 (file)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -54,6 +54,7 @@ static struct buffer_head *ext4_append(handle_t *handle,
                                        struct inode *inode,
                                        ext4_lblk_t *block)
 {
+       struct ext4_map_blocks map;
        struct buffer_head *bh;
        int err;
 
@@ -63,6 +64,21 @@ static struct buffer_head *ext4_append(handle_t *handle,
                return ERR_PTR(-ENOSPC);
 
        *block = inode->i_size >> inode->i_sb->s_blocksize_bits;
+       map.m_lblk = *block;
+       map.m_len = 1;
+
+       /*
+        * We're appending new directory block. Make sure the block is not
+        * allocated yet, otherwise we will end up corrupting the
+        * directory.
+        */
+       err = ext4_map_blocks(NULL, inode, &map, 0);
+       if (err < 0)
+               return ERR_PTR(err);
+       if (err) {
+               EXT4_ERROR_INODE(inode, "Logical block already allocated");
+               return ERR_PTR(-EFSCORRUPTED);
+       }
 
        bh = ext4_bread(handle, inode, *block, EXT4_GET_BLOCKS_CREATE);
        if (IS_ERR(bh))