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    Subject[PATCH 3.18 119/134] ext2: Fix underflow in ext2_max_size()
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jan Kara <jack@suse.cz>

    commit 1c2d14212b15a60300a2d4f6364753e87394c521 upstream.

    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: yangerkun <yangerkun@huawei.com>
    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext2/super.c | 41 ++++++++++++++++++++++++++---------------
    1 file changed, 26 insertions(+), 15 deletions(-)

    --- a/fs/ext2/super.c
    +++ b/fs/ext2/super.c
    @@ -701,7 +701,8 @@ 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
    @@ -715,24 +716,34 @@ static loff_t ext2_max_size(int bits)
    /* total blocks in file system block size */
    upper_limit >>= (bits - 9);

    -
    - /* indirect blocks */
    - meta_blocks = 1;
    - /* 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;
    -
    + /* 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 */
    + 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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