ext4: avoid eh_entries overflow before insert extent_idx

If eh_entries is equal to (or greater than) eh_max, the operation of
inserting new extent_idx will make number of entries overflow.
So check eh_entries before inserting the new extent_idx.

Although there is no bug case according the code (function
ext4_ext_insert_index is called by ext4_ext_split and ext4_ext_split
is called only if the index block has free space), the right logic
should be "lookup the capacity before insertion".

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index b8acfab..9bec432 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -741,6 +741,16 @@ static int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
                                 logical, le32_to_cpu(curp->p_idx->ei_block));
                return -EIO;
        }
+
+       if (unlikely(le16_to_cpu(curp->p_hdr->eh_entries)
+                            >= le16_to_cpu(curp->p_hdr->eh_max))) {
+               EXT4_ERROR_INODE(inode,
+                                "eh_entries %d >= eh_max %d!",
+                                le16_to_cpu(curp->p_hdr->eh_entries),
+                                le16_to_cpu(curp->p_hdr->eh_max));
+               return -EIO;
+       }
+
        len = EXT_MAX_INDEX(curp->p_hdr) - curp->p_idx;
        if (logical > le32_to_cpu(curp->p_idx->ei_block)) {
                /* insert after */
@@ -770,14 +780,6 @@ static int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
        ext4_idx_store_pblock(ix, ptr);
        le16_add_cpu(&curp->p_hdr->eh_entries, 1);
 
-       if (unlikely(le16_to_cpu(curp->p_hdr->eh_entries)
-                            > le16_to_cpu(curp->p_hdr->eh_max))) {
-               EXT4_ERROR_INODE(inode,
-                                "eh_entries %d > eh_max %d!",
-                                le16_to_cpu(curp->p_hdr->eh_entries),
-                                le16_to_cpu(curp->p_hdr->eh_max));
-               return -EIO;
-       }
        if (unlikely(ix > EXT_LAST_INDEX(curp->p_hdr))) {
                EXT4_ERROR_INODE(inode, "ix > EXT_LAST_INDEX!");
                return -EIO;