ext4: Make the extent validity check more paranoid

Instead of just checking that the extent block number is greater or
equal than s_first_data_block, make sure it it is not pointing into
the block group descriptors, since that is clearly wrong.  This helps
prevent filesystem from getting very badly corrupted in case an extent
block is corrupted.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 6132353dcf62a5a167d62d6d34f2343fd5a4533a..c28ffe2595066b903a182dfc9ab0c175de90006f 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -326,11 +326,14 @@ ext4_ext_max_entries(struct inode *inode, int depth)
 
 static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
 {
-       ext4_fsblk_t block = ext_pblock(ext);
+       ext4_fsblk_t block = ext_pblock(ext), valid_block;
        int len = ext4_ext_get_actual_len(ext);
        struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
-       if (unlikely(block < le32_to_cpu(es->s_first_data_block) ||
-                       ((block + len) > ext4_blocks_count(es))))
+
+       valid_block = le32_to_cpu(es->s_first_data_block) +
+               EXT4_SB(inode->i_sb)->s_gdb_count;
+       if (unlikely(block <= valid_block ||
+                    ((block + len) > ext4_blocks_count(es))))
                return 0;
        else
                return 1;
@@ -339,10 +342,13 @@ static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
 static int ext4_valid_extent_idx(struct inode *inode,
                                struct ext4_extent_idx *ext_idx)
 {
-       ext4_fsblk_t block = idx_pblock(ext_idx);
+       ext4_fsblk_t block = idx_pblock(ext_idx), valid_block;
        struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
-       if (unlikely(block < le32_to_cpu(es->s_first_data_block) ||
-                       (block >= ext4_blocks_count(es))))
+
+       valid_block = le32_to_cpu(es->s_first_data_block) +
+               EXT4_SB(inode->i_sb)->s_gdb_count;
+       if (unlikely(block <= valid_block ||
+                    (block >= ext4_blocks_count(es))))
                return 0;
        else
                return 1;