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

[Ondrej Mosnacek]

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>
---
 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