audit: add saddr_fam filter field

Provide a method to filter out sockaddr and bind calls by network
address family.

Existing SOCKADDR records are listed for any network activity.
Implement the AUDIT_SADDR_FAM field selector to be able to classify or
limit records to specific network address families, such as AF_INET or
AF_INET6.

An example of a network record that is unlikely to be useful and flood
the logs:

type=SOCKADDR msg=audit(07/27/2017 12:18:27.019:845) : saddr={ fam=local
path=/var/run/nscd/socket }
type=SYSCALL msg=audit(07/27/2017 12:18:27.019:845) : arch=x86_64
syscall=connect success=no exit=ENOENT(No such file or directory) a0=0x3
a1=0x7fff229c4980 a2=0x6e a3=0x6 items=1 ppid=3301 pid=6145 auid=sgrubb
uid=sgrubb gid=sgrubb euid=sgrubb suid=sgrubb fsuid=sgrubb egid=sgrubb
sgid=sgrubb fsgid=sgrubb tty=pts3 ses=4 comm=bash exe=/usr/bin/bash
subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
key=network-test

Please see the audit-testsuite PR at
https://github.com/linux-audit/audit-testsuite/pull/87
Please see the github issue
https://github.com/linux-audit/audit-kernel/issues/64
Please see the github issue for the accompanying userspace support
https://github.com/linux-audit/audit-userspace/issues/93

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: merge fuzz in auditfilter.c]
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/auditfilter.c

@@ -391,6 +391,7 @@ static int audit_field_valid(struct audit_entry *entry, struct audit_field *f)
 	case AUDIT_SUBJ_CLR:
 	case AUDIT_OBJ_LEV_LOW:
 	case AUDIT_OBJ_LEV_HIGH:
+	case AUDIT_SADDR_FAM:
 		/* bit ops are only useful on syscall args */
 		if (f->op == Audit_bitmask || f->op == Audit_bittest)
 			return -EINVAL;
@@ -438,6 +439,10 @@ static int audit_field_valid(struct audit_entry *entry, struct audit_field *f)
 		if (f->val > AUDIT_MAX_FIELD_COMPARE)
 			return -EINVAL;
 		break;
+	case AUDIT_SADDR_FAM:
+		if (f->val >= AF_MAX)
+			return -EINVAL;
+		break;
 	default:
 		break;
 	}