Re: [PATCH] ext4: Fix loff_t overflow in ext4_max_bitmap_size()
From: Jan Kara <jack@suse.cz>
Date: 2021-06-07 10:00:30
On Sat 05-06-21 10:39:32, Ritesh Harjani wrote:
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 <redacted>
OK, this works (although it's really tight ;). Won't it be somewhat safer if we compared upper_limit and res before shifting both by blocksize_bits to the left? Basically we need to shift only for comparison with MAX_LFS_FILESIZE which is in bytes... But either way feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza
quoted hunk ↗ jump to hunk
--- fs/ext4/super.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 7dc94f3e18e6..bedb66386966 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c@@ -3189,17 +3189,17 @@ 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@@ -3242,7 +3242,7 @@ 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,-- 2.31.1
-- Jan Kara [off-list ref] SUSE Labs, CR