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    Subject[PATCH 4.7 36/41] ext4: check for extents that wrap around
    Date
    4.7-stable review patch.  If anyone has any objections, please let me know.

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

    From: Vegard Nossum <vegard.nossum@oracle.com>

    commit f70749ca42943faa4d4dcce46dfdcaadb1d0c4b6 upstream.

    An extent with lblock = 4294967295 and len = 1 will pass the
    ext4_valid_extent() test:

    ext4_lblk_t last = lblock + len - 1;

    if (len == 0 || lblock > last)
    return 0;

    since last = 4294967295 + 1 - 1 = 4294967295. This would later trigger
    the BUG_ON(es->es_lblk + es->es_len < es->es_lblk) in ext4_es_end().

    We can simplify it by removing the - 1 altogether and changing the test
    to use lblock + len <= lblock, since now if len = 0, then lblock + 0 ==
    lblock and it fails, and if len > 0 then lblock + len > lblock in order
    to pass (i.e. it doesn't overflow).

    Fixes: 5946d0893 ("ext4: check for overlapping extents in ext4_valid_extent_entries()")
    Fixes: 2f974865f ("ext4: check for zero length extent explicitly")
    Cc: Eryu Guan <guaneryu@gmail.com>
    Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
    Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/extents.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    --- a/fs/ext4/extents.c
    +++ b/fs/ext4/extents.c
    @@ -381,9 +381,13 @@ static int ext4_valid_extent(struct inod
    ext4_fsblk_t block = ext4_ext_pblock(ext);
    int len = ext4_ext_get_actual_len(ext);
    ext4_lblk_t lblock = le32_to_cpu(ext->ee_block);
    - ext4_lblk_t last = lblock + len - 1;

    - if (len == 0 || lblock > last)
    + /*
    + * We allow neither:
    + * - zero length
    + * - overflow/wrap-around
    + */
    + if (lblock + len <= lblock)
    return 0;
    return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
    }

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