ACK/Cmnt: [PATCH][eoan] UBUNTU: SAUCE: apparmor: fix nnp subset test for unconfined

[Stefan Bader]

On 03.10.19 21:14, John Johansen wrote:
> The subset test is not taking into account the unconfined exception
> which will cause profile transitions in the stacked confinement
> case to fail when no_new_privs is applied.
> 
> This fixes a regression introduced in the 4.17 kernel caused by the
> reworking of domain transitions.
> 
> Fixes: 9fcf78cca1986 ("apparmor: update domain transitions that are subsets of confinement at nnp")
> BugLink: https://bugs.launchpad.net/bugs/1844186
> Signed-off-by: John Johansen <john.johansen at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

With some more background info it is still mind bending due to the many levels
of inversion in the logic. Like aa_subset_is_unconfined_subset() which takes
quite some time to parse. I think in the end it is a "subset does not add
further restrictions". This is tested with !confined.
Then that result is taken inverted again to fail when switching profiles. So in
the end its a "allow additional unconfined profiles" thing.

-Stefan

>  security/apparmor/domain.c        |  8 ++++----
>  security/apparmor/include/label.h |  1 +
>  security/apparmor/label.c         | 33 +++++++++++++++++++++++++++++++
>  3 files changed, 38 insertions(+), 4 deletions(-)
> 
> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
> index 9e0492795267..776e8f76aef3 100644
> --- a/security/apparmor/domain.c
> +++ b/security/apparmor/domain.c
> @@ -931,7 +931,7 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
>  	 * aways results in a further reduction of permissions.
>  	 */
>  	if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
> -	    !unconfined(label) && !aa_label_is_subset(new, ctx->nnp)) {
> +	    !unconfined(label) && !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>  		error = -EPERM;
>  		info = "no new privs";
>  		goto audit;
> @@ -1209,7 +1209,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>  		 * reduce restrictions.
>  		 */
>  		if (task_no_new_privs(current) && !unconfined(label) &&
> -		    !aa_label_is_subset(new, ctx->nnp)) {
> +		    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>  			/* not an apparmor denial per se, so don't log it */
>  			AA_DEBUG("no_new_privs - change_hat denied");
>  			error = -EPERM;
> @@ -1230,7 +1230,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>  		 * reduce restrictions.
>  		 */
>  		if (task_no_new_privs(current) && !unconfined(label) &&
> -		    !aa_label_is_subset(previous, ctx->nnp)) {
> +		    !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
>  			/* not an apparmor denial per se, so don't log it */
>  			AA_DEBUG("no_new_privs - change_hat denied");
>  			error = -EPERM;
> @@ -1426,7 +1426,7 @@ int aa_change_profile(const char *fqname, int flags)
>  		 * reduce restrictions.
>  		 */
>  		if (task_no_new_privs(current) && !unconfined(label) &&
> -		    !aa_label_is_subset(new, ctx->nnp)) {
> +		    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>  			/* not an apparmor denial per se, so don't log it */
>  			AA_DEBUG("no_new_privs - change_hat denied");
>  			error = -EPERM;
> diff --git a/security/apparmor/include/label.h b/security/apparmor/include/label.h
> index 56be4412d84e..b1aeb282ca22 100644
> --- a/security/apparmor/include/label.h
> +++ b/security/apparmor/include/label.h
> @@ -281,6 +281,7 @@ bool aa_label_init(struct aa_label *label, int size);
>  struct aa_label *aa_label_alloc(int size, struct aa_proxy *proxy, gfp_t gfp);
>  
>  bool aa_label_is_subset(struct aa_label *set, struct aa_label *sub);
> +bool aa_label_is_unconfined_subset(struct aa_label *set, struct aa_label *sub);
>  struct aa_profile *__aa_label_next_not_in_set(struct label_it *I,
>  					     struct aa_label *set,
>  					     struct aa_label *sub);
> diff --git a/security/apparmor/label.c b/security/apparmor/label.c
> index 3fa3e56f0e05..d94cf3d10877 100644
> --- a/security/apparmor/label.c
> +++ b/security/apparmor/label.c
> @@ -551,6 +551,39 @@ bool aa_label_is_subset(struct aa_label *set, struct aa_label *sub)
>  	return __aa_label_next_not_in_set(&i, set, sub) == NULL;
>  }
>  
> +/**
> + * aa_label_is_unconfined_subset - test if @sub is a subset of @set
> + * @set: label to test against
> + * @sub: label to test if is subset of @set
> + *
> + * This checks for subset but taking into account unconfined. IF
> + * @sub contains an unconfined profile that does not have a matching
> + * unconfined in @set then this will not cause the test to fail.
> + * Conversely we don't care about an unconfined in @set that is not in
> + * @sub
> + *
> + * Returns: true if @sub is special_subset of @set
> + *     else false
> + */
> +bool aa_label_is_unconfined_subset(struct aa_label *set, struct aa_label *sub)
> +{
> +	struct label_it i = { };
> +	struct aa_profile *p;
> +
> +	AA_BUG(!set);
> +	AA_BUG(!sub);
> +
> +	if (sub == set)
> +		return true;
> +
> +	do {
> +		p = __aa_label_next_not_in_set(&i, set, sub);
> +		if (p && !profile_unconfined(p))
> +			break;
> +	} while (p);
> +
> +	return p == NULL;
> +}
>  
>  
>  /**
> 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: OpenPGP digital signature
URL: <https://lists.ubuntu.com/archives/kernel-team/attachments/20191009/1ca05038/attachment-0001.sig>