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 <daniel@iogearbox.net>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 2 deletions

diff --git a/net/compat.c b/net/compat.c
index 1373947efb50..1cd2ec046164 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -309,8 +309,8 @@ void scm_detach_fds_compat(struct msghdr *kmsg, struct scm_cookie *scm)
         __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));
@@ -323,6 +323,19 @@ static int do_set_attach_filter(struct socket *sock, int level, int optname,
             __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,