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>

1 files changed, 10 insertions, 8 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index b8acfab00224..9bec432e2d26 100644
--- 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;