On Fri, 2020-01-31 at 14:02 +0000, Roberto Sassu wrote: > > -----Original Message----- > > From: linux-integrity-owner@xxxxxxxxxxxxxxx [mailto:linux-integrity- > > owner@xxxxxxxxxxxxxxx] On Behalf Of Mimi Zohar > > Sent: Thursday, January 30, 2020 11:26 PM > > To: Roberto Sassu <roberto.sassu@xxxxxxxxxx>; > > jarkko.sakkinen@xxxxxxxxxxxxxxx; > > james.bottomley@xxxxxxxxxxxxxxxxxxxxx; linux-integrity@xxxxxxxxxxxxxxx > > Cc: linux-security-module@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > Silviu Vlasceanu <Silviu.Vlasceanu@xxxxxxxxxx> > > Subject: Re: [PATCH 7/8] ima: use ima_hash_algo for collision detection in > > the measurement list > > > > On Mon, 2020-01-27 at 18:04 +0100, Roberto Sassu wrote: > > > Before calculating a digest for each PCR bank, collisions were detected > > > with a SHA1 digest. This patch includes ima_hash_algo among the > > algorithms > > > used to calculate the template digest and checks collisions on that digest. > > > > > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > Definitely needed to protect against a sha1 collision attack. > > > > <snip> > > > > > > > > diff --git a/security/integrity/ima/ima_api.c > > b/security/integrity/ima/ima_api.c > > > index ebaf0056735c..a9bb45de6db9 100644 > > > --- a/security/integrity/ima/ima_api.c > > > +++ b/security/integrity/ima/ima_api.c > > > @@ -51,7 +51,7 @@ int ima_alloc_init_template(struct ima_event_data > > *event_data, > > > if (!*entry) > > > return -ENOMEM; > > > > > > - (*entry)->digests = kcalloc(ima_tpm_chip->nr_allocated_banks + 1, > > > + (*entry)->digests = kcalloc(ima_tpm_chip->nr_allocated_banks + 2, > > > sizeof(*(*entry)->digests), GFP_NOFS); > > > if (!(*entry)->digests) { > > > result = -ENOMEM; > > > > I would prefer not having to allocate and use "nr_allocated_banks + 1" > > everywhere, but I understand the need for it. I'm not sure this patch > > warrants allocating +2. Perhaps, if a TPM bank doesn't exist for the > > IMA default hash algorithm, use a different algorithm or, worst case, > > continue using the ima_sha1_idx. > > We could introduce a new option called ima_hash_algo_tpm to specify > the algorithm of an allocated bank. We can use this for boot_aggregate > and hash collision detection. I don't think that would work in the case where the IMA default hash is set to sha256, but the system has a TPM 1.2 chip. We would be left using SHA1 for the file hash collision detection. With my suggestion of defining an "extra" variable, I kind of back tracked here. There are two problems that I'm trying to address - hard coding the number of additional "banks" and unnecessarily allocating more memory than necessary. By pre-walking the list, calculating the "extra" banks, you'll resolve both issues. Mimi
