ext4: only use i_size_high for regular files

Directories are not allowed to be bigger than 2GB, so don't use
i_size_high for anything other than regular files.  E2fsck should
complain about these inodes, but the simplest thing to do for the
kernel is to only use i_size_high for regular files.

This prevents an intentially corrupted filesystem from causing the
kernel to burn a huge amount of CPU and issuing error messages such
as:

EXT4-fs warning (device loop0): ext4_block_to_path: block 135090028 > max

Thanks to David Maciejak from Fortinet's FortiGuard Global Security
Research Team for reporting this issue.

http://bugzilla.kernel.org/show_bug.cgi?id=12375

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

2 files changed, 7 insertions, 4 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index c668e4377d7..aafc9eba1c2 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1206,8 +1206,11 @@ static inline void ext4_r_blocks_count_set(struct ext4_super_block *es,
 
 static inline loff_t ext4_isize(struct ext4_inode *raw_inode)
 {
-        return ((loff_t)le32_to_cpu(raw_inode->i_size_high) << 32) |
-                le32_to_cpu(raw_inode->i_size_lo);
+        if (S_ISREG(le16_to_cpu(raw_inode->i_mode)))
+                return ((loff_t)le32_to_cpu(raw_inode->i_size_high) << 32) |
+                        le32_to_cpu(raw_inode->i_size_lo);
+        else
+                return (loff_t) le32_to_cpu(raw_inode->i_size_lo);
 }
 
 static inline void ext4_isize_set(struct ext4_inode *raw_inode, loff_t i_size)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a6444cee0c7..49484ba801c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -360,9 +360,9 @@ static int ext4_block_to_path(struct inode *inode,
                 final = ptrs;
         } else {
                 ext4_warning(inode->i_sb, "ext4_block_to_path",
-                                "block %lu > max",
+                                "block %lu > max in inode %lu",
                                 i_block + direct_blocks +
-                                indirect_blocks + double_blocks);
+                                indirect_blocks + double_blocks, inode->i_ino);
         }
         if (boundary)
                 *boundary = final - 1 - (i_block & (ptrs - 1));