RE: [PATCH v2 3/6] ima: Fix ima digest hash table key calculation

[David Laight]

From: Roberto Sassu
> Sent: 27 April 2020 13:51
...
> > > -static inline unsigned long ima_hash_key(u8 *digest)
> > > +static inline unsigned int ima_hash_key(u8 *digest)
> > >  {
> > > -	return hash_long(*digest, IMA_HASH_BITS);
> > > +	return (*(unsigned int *)digest % IMA_MEASURE_HTABLE_SIZE);
> >
> > That almost certainly isn't right.
> > It falls foul of the *(integer_type *)ptr being almost always wrong.
> 
> I didn't find the problem. Can you please explain?

The general problem with *(int_type *)ptr is that it does completely
the wrong thing if 'ptr' is the address of a larger integer type on
a big-endian system.
You may also get a misaligned access trap.

In this case I guess that digest is actually u8[SHA1_DIGEST_SIZE].
Maybe what you should return is:
	(digest[0] | digest[1] << 8) % IMA_MEASURE_HTABLE_SIZE;
and comment that there is no point taking a hash of part of
a SHA1 digest.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)