• Nicolai Stange's avatar
    lib/mpi: mpi_read_raw_from_sgl(): fix nbits calculation · 64c09b0b
    Nicolai Stange authored
    The number of bits, nbits, is calculated in mpi_read_raw_from_sgl() as
    follows:
    
      nbits = nbytes * 8;
    
    Afterwards, the number of leading zero bits of the first byte get
    subtracted:
    
      nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
    
    However, count_leading_zeros() takes an unsigned long and thus,
    the u8 gets promoted to an unsigned long.
    
    Thus, the above doesn't subtract the number of leading zeros in the most
    significant nonzero input byte from nbits, but the number of leading
    zeros of the most significant nonzero input byte promoted to unsigned long,
    i.e. BITS_PER_LONG - 8 too many.
    
    Fix this by subtracting
    
      count_leading_zeros(...) - (BITS_PER_LONG - 8)
    
    from nbits only.
    
    Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
    Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    64c09b0b
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