Re: [PATCH v3 2/2] ima-evm-utils: log unknown keyid's as errors

[Vitaly Chikunov <vt@altlinux.org>]

Mimi,

On Tue, Jul 23, 2019 at 06:59:16PM -0400, Mimi Zohar wrote:
> On Wed, 2019-07-24 at 01:18 +0300, Vitaly Chikunov wrote:
> > On Thu, Jul 18, 2019 at 10:29:54AM -0400, Mimi Zohar wrote:
> > > Each tima a new unknown key is encountered, emit a message of the format
> > > "key #: <keyid> unknown".  The individual files using unknown keys are
> > > then only logged in verbose mode.
> > > 
> > > Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> > > ---
> > >  src/libimaevm.c | 21 +++++++++++++++++----
> > >  1 file changed, 17 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/src/libimaevm.c b/src/libimaevm.c
> > > index 43eb4ef2412c..d2194a6ca0f8 100644
> > > --- a/src/libimaevm.c
> > > +++ b/src/libimaevm.c
> > > @@ -402,13 +402,26 @@ static struct public_key_entry *public_keys = NULL;
> > >  
> > >  static EVP_PKEY *find_keyid(uint32_t keyid)
> > >  {
> > > -	struct public_key_entry *entry;
> > > +	struct public_key_entry *entry, *tail = public_keys;
> > 
> > If user specified in `-k` filename that does not exist no key is added
> > into public_keys and it remains NULL.
> 
> Right, just the keyid is added and an error message is emitted.
> 
> > 
> > > +	int i = 1;
> > >  
> > >  	for (entry = public_keys; entry != NULL; entry = entry->next) {
> > >  		if (entry->keyid == keyid)
> > >  			return entry->key;
> > > +		i++;
> > > +		tail = entry;
> > >  	}
> > > -	return NULL;
> > > +
> > > +	/* add unknown keys to list */
> > > +	entry = calloc(1, sizeof(struct public_key_entry));
> > > +	if (!entry) {
> > > +		perror("calloc");
> > > +		return 0;
> > > +	}
> > > +	entry->keyid = keyid;
> > > +	tail->next = entry;
> > 
> > In that case here is SIGSEGV when user try to ima_verify.
> 
> find_keyid() returns NULL, which is checked before being used.
>  There's only one caller of this function.

find_keyid does not return since tail is NULL, thus there is null
dereference in `tail->next`.

> Do you have a test case to reproduce this bug?

  ima-evm-utils/tests ((31b5f50...))$ rm sha1.txt
  ima-evm-utils/tests ((31b5f50...))$ touch sha1.txt
  ima-evm-utils/tests ((31b5f50...))$ evmctl ima_sign -k test-rsa1024.key -a sha1 --xattr-user sha1.txt
  ima-evm-utils/tests ((31b5f50...))$ evmctl ima_verify -k /absent --xattr-user sha1.txt
  Failed to open keyfile: /absent
  Segmentation fault

31b5f50 is head of your git next branch.

I temporary fixed like this:

-       tail->next = entry;
+       if (tail)
+               tail->next = entry;
+       else
+               public_keys = entry;