Fix LOCAL_PEERCRED in 32-bit compat mode

Previously the cr_pid field would be incorrectly copied to userland, due
to a size mismatch between the structure as defined in 32-bit vs 64-bit
builds.  Fix it by converting the structure before copying it to
userland.

PR:		294833
Sponsored by:	ConnectWise
MFC after:	1 week
Reviewed by:	emaste
Differential Revision: https://reviews.freebsd.org/D56675

sys/kern/uipc_usrreq.c

@@ -83,6 +83,7 @@
 #include <sys/socketvar.h>
 #include <sys/signalvar.h>
 #include <sys/stat.h>
+#include <sys/sysent.h>
 #include <sys/sx.h>
 #include <sys/sysctl.h>
 #include <sys/systm.h>
@@ -2752,8 +2753,24 @@ uipc_ctloutput(struct socket *so, struct sockopt *sopt)
 					error = EINVAL;
 			}
 			UNP_PCB_UNLOCK(unp);
-			if (error == 0)
-				error = sooptcopyout(sopt, &xu, sizeof(xu));
+			if (error != 0)
+				break;
+#ifdef COMPAT_FREEBSD32
+			if (SV_PROC_FLAG(sopt->sopt_td->td_proc, SV_ILP32)) {
+				struct xucred32 xu32 = {};
+				int i;
+
+				xu32.cr_version = xu.cr_version;
+				xu32.cr_uid = xu.cr_uid;
+				xu32.cr_ngroups = xu.cr_ngroups;
+				for (i = 0; i < XU_NGROUPS; i++)
+					xu32.cr_groups[i] = xu.cr_groups[i];
+				xu32.cr_pid = xu.cr_pid;
+				error = sooptcopyout(sopt, &xu32, sizeof(xu32));
+				break;
+			}
+#endif
+			error = sooptcopyout(sopt, &xu, sizeof(xu));
 			break;
 
 		case LOCAL_CREDS:

sys/sys/ucred.h

@@ -193,6 +193,17 @@ struct setcred32 {
 	uint32_t sc_label;		/* struct mac32 [*] */
 };
 
+#ifdef COMPAT_FREEBSD32
+/* 32-bit compatible version of xucred */
+struct xucred32 {
+	u_int	cr_version;		/* structure layout version */
+	uid_t	cr_uid;			/* effective user id */
+	short	cr_ngroups;		/* number of groups (incl. cr_gid). */
+	gid_t	cr_groups[XU_NGROUPS];	/* groups */
+	pid_t	cr_pid;
+};
+#endif
+
 struct thread;
 
 /* Common native and 32-bit compatibility entry point. */