ext4: fix loff_t overflow in ext4_max_bitmap_size()

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>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a52f1572daa535d5c3dc0b49b0accddb9f09b1ad..9b5b2f63b470839ea7342e7eb51e0af8aaac8da1 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3030,17 +3030,17 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)
  */
 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
@@ -3083,7 +3083,7 @@ static loff_t ext4_max_bitmap_size(int bits, int has_huge_files)
        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,