packet: compat support for sock_fprog

Socket option PACKET_FANOUT_DATA takes a struct sock_fprog as argument
if PACKET_FANOUT has mode PACKET_FANOUT_CBPF. This structure contains
a pointer into user memory. If userland is 32-bit and kernel is 64-bit
the two disagree about the layout of struct sock_fprog.

Add compat setsockopt support to convert a 32-bit compat_sock_fprog to
a 64-bit sock_fprog. This is analogous to compat_sock_fprog support for
SO_REUSEPORT added in commit 1957598840f4 ("soreuseport: add compat
case for setsockopt SO_ATTACH_REUSEPORT_CBPF").

Reported-by: Daniel Borkmann <[e-mail]>
Signed-off-by: Willem de Bruijn <[e-mail]>
Acked-by: Daniel Borkmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/compat.h

···
 
 int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *,
 		      struct sockaddr __user **, struct iovec **);
+struct sock_fprog __user *get_compat_bpf_fprog(char __user *optval);
 asmlinkage long compat_sys_sendmsg(int, struct compat_msghdr __user *,
 				   unsigned int);
 asmlinkage long compat_sys_sendmmsg(int, struct compat_mmsghdr __user *,

net/compat.c

···
 	__scm_destroy(scm);
 }
 
-static int do_set_attach_filter(struct socket *sock, int level, int optname,
-				char __user *optval, unsigned int optlen)
+/* allocate a 64-bit sock_fprog on the user stack for duration of syscall. */
+struct sock_fprog __user *get_compat_bpf_fprog(char __user *optval)
 {
 	struct compat_sock_fprog __user *fprog32 = (struct compat_sock_fprog __user *)optval;
 	struct sock_fprog __user *kfprog = compat_alloc_user_space(sizeof(struct sock_fprog));
···
 	    __get_user(ptr, &fprog32->filter) ||
 	    __put_user(len, &kfprog->len) ||
 	    __put_user(compat_ptr(ptr), &kfprog->filter))
+		return NULL;
+
+	return kfprog;
+}
+EXPORT_SYMBOL_GPL(get_compat_bpf_fprog);
+
+static int do_set_attach_filter(struct socket *sock, int level, int optname,
+				char __user *optval, unsigned int optlen)
+{
+	struct sock_fprog __user *kfprog;
+
+	kfprog = get_compat_bpf_fprog(optval);
+	if (!kfprog)
 		return -EFAULT;
 
 	return sock_setsockopt(sock, level, optname, (char __user *)kfprog,

net/packet/af_packet.c

···
 #include <net/inet_common.h>
 #endif
 #include <linux/bpf.h>
+#include <net/compat.h>
 
 #include "internal.h"
 
···
 }
 
 
+#ifdef CONFIG_COMPAT
+static int compat_packet_setsockopt(struct socket *sock, int level, int optname,
+				    char __user *optval, unsigned int optlen)
+{
+	struct packet_sock *po = pkt_sk(sock->sk);
+
+	if (level != SOL_PACKET)
+		return -ENOPROTOOPT;
+
+	if (optname == PACKET_FANOUT_DATA &&
+	    po->fanout && po->fanout->type == PACKET_FANOUT_CBPF) {
+		optval = (char __user *)get_compat_bpf_fprog(optval);
+		if (!optval)
+			return -EFAULT;
+		optlen = sizeof(struct sock_fprog);
+	}
+
+	return packet_setsockopt(sock, level, optname, optval, optlen);
+}
+#endif
+
 static int packet_notifier(struct notifier_block *this,
 			   unsigned long msg, void *ptr)
 {
···
 	.shutdown =	sock_no_shutdown,
 	.setsockopt =	packet_setsockopt,
 	.getsockopt =	packet_getsockopt,
+#ifdef CONFIG_COMPAT
+	.compat_setsockopt = compat_packet_setsockopt,
+#endif
 	.sendmsg =	packet_sendmsg,
 	.recvmsg =	packet_recvmsg,
 	.mmap =		packet_mmap,