[PATCH 4.14 53/64] ext4: avoid arithemetic overflow that can trigger a BUG

From: Greg Kroah-Hartman
Date: Thu Sep 27 2018 - 05:24:00 EST


4.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@xxxxxxx>

commit bcd8e91f98c156f4b1ebcfacae675f9cfd962441 upstream.

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@xxxxxxx>
Reported-by: Wen Xu <wen.xu@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/ext4/ext4.h | 3 +++
fs/ext4/inode.c | 9 +++++++--
2 files changed, 10 insertions(+), 2 deletions(-)

--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -714,6 +714,9 @@ struct fsxattr {
/* 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
*/
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3407,11 +3407,16 @@ static int ext4_iomap_begin(struct inode
{
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
unsigned int blkbits = inode->i_blkbits;
- unsigned long first_block = offset >> blkbits;
- unsigned long last_block = (offset + length - 1) >> blkbits;
+ unsigned long first_block, last_block;
struct ext4_map_blocks map;
int ret;

+ if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK)
+ return -EINVAL;
+ first_block = offset >> blkbits;
+ last_block = min_t(loff_t, (offset + length - 1) >> blkbits,
+ EXT4_MAX_LOGICAL_BLOCK);
+
if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
return -ERANGE;