• Willy Tarreau's avatar
    lzo: check for length overrun in variable length encoding. · 72cf9012
    Willy Tarreau authored
    This fix ensures that we never meet an integer overflow while adding
    255 while parsing a variable length encoding. It works differently from
    commit 206a81c1 ("lzo: properly check for overruns") because instead of
    ensuring that we don't overrun the input, which is tricky to guarantee
    due to many assumptions in the code, it simply checks that the cumulated
    number of 255 read cannot overflow by bounding this number.
    
    The MAX_255_COUNT is the maximum number of times we can add 255 to a base
    count without overflowing an integer. The multiply will overflow when
    multiplying 255 by more than MAXINT/255. The sum will overflow earlier
    depending on the base count. Since the base count is taken from a u8
    and a few bits, it is safe to assume that it will always be lower than
    or equal to 2*255, thus we can always prevent any overflow by accepting
    two less 255 steps.
    
    This patch also reduces the CPU overhead and actually increases performance
    by 1.1% compared to the initial code, while the previous fix costs 3.1%
    (measured on x86_64).
    
    The fix needs to be backported to all currently supported stable kernels.
    Reported-by: 's avatarWillem Pinckaers <willem@lekkertech.net>
    Cc: "Don A. Bailey" <donb@securitymouse.com>
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: 's avatarWilly Tarreau <w@1wt.eu>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    72cf9012