[PATCH 5.4 41/56] ext4: fix loff_t overflow in ext4_max_bitmap_size()

Greg Kroah-Hartman
2021-10-04T13:18:18Z

From: Ritesh Harjani <riteshh@linux.ibm.com>

commit 75ca6ad408f459f00b09a64f04c774559848c097 upstream.

We should use unsigned long long rather than loff_t to avoid
overflow in ext4_max_bitmap_size() for comparison before returning.
w/o this patch sbi->s_bitmap_maxbytes was becoming a negative
value due to overflow of upper_limit (with has_huge_files as true)

Below is a quick test to trigger it on a 64KB pagesize system.

sudo mkfs.ext4 -b 65536 -O ^has_extents,^64bit /dev/loop2
sudo mount /dev/loop2 /mnt
sudo echo "hello" > /mnt/hello -> This will error out with
"echo: write error: File too large"

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/594f409e2c543e90fd836b78188dfa5c575065ba.1622867594.git.riteshh@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/super.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2830,17 +2830,17 @@ static loff_t ext4_max_size(int blkbits,
*/
static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
{
- loff_t res = EXT4_NDIR_BLOCKS;
+ unsigned long long upper_limit, res = EXT4_NDIR_BLOCKS;
int meta_blocks;
- loff_t upper_limit;
- /* This is calculated to be the largest file size for a dense, block
+
+ /*
+ * This is calculated to be the largest file size for a dense, block
* mapped file such that the file's total number of 512-byte sectors,
* including data and all indirect blocks, does not exceed (2^48 - 1).
*
* __u32 i_blocks_lo and _u16 i_blocks_high represent the total
* number of 512-byte sectors of the file.
*/
-
if (!has_huge_files) {
/*
* !has_huge_files or implies that the inode i_block field
@@ -2883,7 +2883,7 @@ static loff_t ext4_max_bitmap_size(int b
if (res > MAX_LFS_FILESIZE)
res = MAX_LFS_FILESIZE;

- return res;
+ return (loff_t)res;
}

static ext4_fsblk_t descriptor_loc(struct super_block *sb,