Commit 1c2d1421 authored by Jan Kara's avatar Jan Kara
Browse files

ext2: Fix underflow in ext2_max_size() 



When ext2 filesystem is created with 64k block size, ext2_max_size()
will return value less than 0. Also, we cannot write any file in this fs
since the sb->maxbytes is less than 0. The core of the problem is that
the size of block index tree for such large block size is more than
i_blocks can carry. So fix the computation to count with this
possibility.

File size limits computed with the new function for the full range of
possible block sizes look like:

bits file_size
10     17247252480
11    275415851008
12   2196873666560
13   2197948973056
14   2198486220800
15   2198754754560
16   2198888906752

CC: stable@vger.kernel.org
Reported-by: default avataryangerkun <yangerkun@huawei.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
parent 4bc74ba1

fs/ext2/super.c

+25 −14
Original line number Diff line number Diff line
@@ -757,7 +757,8 @@ static loff_t ext2_max_size(int bits) 
{

	loff_t res = EXT2_NDIR_BLOCKS;

	int meta_blocks;

	loff_t upper_limit;

	unsigned int upper_limit;

	unsigned int ppb = 1 << (bits-2);



	/* This is calculated to be the largest file size for a

	 * dense, file such that the total number of
@@ -771,24 +772,34 @@ static loff_t ext2_max_size(int bits) 
	/* total blocks in file system block size */

	upper_limit >>= (bits - 9);



	/* Compute how many blocks we can address by block tree */

	res += 1LL << (bits-2);

	res += 1LL << (2*(bits-2));

	res += 1LL << (3*(bits-2));

	/* Does block tree limit file size? */

	if (res < upper_limit)

		goto check_lfs;



	res = upper_limit;

	/* How many metadata blocks are needed for addressing upper_limit? */

	upper_limit -= EXT2_NDIR_BLOCKS;

	/* indirect blocks */

	meta_blocks = 1;

	upper_limit -= ppb;

	/* double indirect blocks */

	meta_blocks += 1 + (1LL << (bits-2));

	/* tripple indirect blocks */

	meta_blocks += 1 + (1LL << (bits-2)) + (1LL << (2*(bits-2)));



	upper_limit -= meta_blocks;

	upper_limit <<= bits;



	res += 1LL << (bits-2);

	res += 1LL << (2*(bits-2));

	res += 1LL << (3*(bits-2));

	if (upper_limit < ppb * ppb) {

		meta_blocks += 1 + DIV_ROUND_UP(upper_limit, ppb);

		res -= meta_blocks;

		goto check_lfs;

	}

	meta_blocks += 1 + ppb;

	upper_limit -= ppb * ppb;

	/* tripple indirect blocks for the rest */

	meta_blocks += 1 + DIV_ROUND_UP(upper_limit, ppb) +

		DIV_ROUND_UP(upper_limit, ppb*ppb);

	res -= meta_blocks;

check_lfs:

	res <<= bits;

	if (res > upper_limit)

		res = upper_limit;



	if (res > MAX_LFS_FILESIZE)

		res = MAX_LFS_FILESIZE;

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