ext4: avoid arithemetic overflow that can trigger a BUG

A maliciously crafted file system can cause an overflow when the
results of a 64-bit calculation is stored into a 32-bit length
parameter.

https://bugzilla.kernel.org/show_bug.cgi?id=200623

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Wen Xu <wen.xu@gatech.edu>
Cc: stable@vger.kernel.org

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 249bcee4d7b2..ac05bd86643a 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -686,6 +686,9 @@ enum {
 /* Max physical block we can address w/o extents */
 #define EXT4_MAX_BLOCK_FILE_PHYS        0xFFFFFFFF
 
+/* Max logical block we can support */
+#define EXT4_MAX_LOGICAL_BLOCK          0xFFFFFFFF
+
 /*
  * Structure of an inode on the disk
  */