[PATCH ghak82 v2] audit: Fix extended comparison of GID/EGID

[Richard Guy Briggs]

On 2018-05-31 09:19, Ondrej Mosnacek wrote:
> The audit_filter_rules() function in auditsc.c used the in_[e]group_p()
> functions to check GID/EGID match, but these functions use the current
> task's credentials, while the comparison should use the credentials of
> the task given to audit_filter_rules() as a parameter (tsk).
> 
> Note that we can use group_search(cred->group_info, ...) as a
> replacement for both in_group_p and in_egroup_p as these functions only
> compare the parameter to cred->fsgid/egid and then call group_search.
> 
> In fact, the usage of in_group_p was even more incorrect: it compares to
> cred->fsgid (which is usually equal to cred->egid) and not cred->gid.
> 
> GitHub issue:
> https://github.com/linux-audit/audit-kernel/issues/82
> 
> Fixes: 37eebe39c973 ("audit: improve GID/EGID comparation logic")
> Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>

Given what you've turned up while investigating this, I'm comfortable
with the solution you've presented.

Reviewed-by: Richard Guy Briggs <rgb at redhat.com>

> ---
>  kernel/auditsc.c | 26 ++++++++++++--------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index ceb1c4596c51..3a324ca2fd20 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -492,23 +492,21 @@ static int audit_filter_rules(struct task_struct *tsk,
>  			break;
>  		case AUDIT_GID:
>  			result = audit_gid_comparator(cred->gid, f->op, f->gid);
> -			if (f->op == Audit_equal) {
> -				if (!result)
> -					result = in_group_p(f->gid);
> -			} else if (f->op == Audit_not_equal) {
> -				if (result)
> -					result = !in_group_p(f->gid);
> -			}
> +			if (f->op == Audit_equal)
> +				result = result ||
> +					groups_search(cred->group_info, f->gid);
> +			else if (f->op == Audit_not_equal)
> +				result = result &&
> +					!groups_search(cred->group_info, f->gid);
>  			break;
>  		case AUDIT_EGID:
>  			result = audit_gid_comparator(cred->egid, f->op, f->gid);
> -			if (f->op == Audit_equal) {
> -				if (!result)
> -					result = in_egroup_p(f->gid);
> -			} else if (f->op == Audit_not_equal) {
> -				if (result)
> -					result = !in_egroup_p(f->gid);
> -			}
> +			if (f->op == Audit_equal)
> +				result = result ||
> +					groups_search(cred->group_info, f->gid);
> +			else if (f->op == Audit_not_equal)
> +				result = result &&
> +					!groups_search(cred->group_info, f->gid);
>  			break;
>  		case AUDIT_SGID:
>  			result = audit_gid_comparator(cred->sgid, f->op, f->gid);
> -- 
> 2.17.0
> 

- RGB

--
Richard Guy Briggs <rgb at redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635