sockptr: fix usize check in copy_struct_from_sockptr() for user pointers

copy_struct_from_user will never hit the check_zeroed_user() call
and will never return -E2BIG if new userspace passed new bits in a
larger structure than the current kernel structure.

As far as I can there are no critical/related uapi changes in

- include/net/bluetooth/bluetooth.h and net/bluetooth/sco.c
  after the use of copy_struct_from_sockptr in v6.13-rc3
- include/uapi/linux/tcp.h and net/ipv4/tcp_ao.c
  after the use of copy_struct_from_sockptr in v6.6-rc1

So that new callers will get the correct behavior from the start.

Fixes: 4954f17dde ("net/tcp: Introduce TCP_AO setsockopt()s")
Fixes: ef84703a91 ("net/tcp: Add TCP-AO getsockopt()s")
Fixes: faadfaba5e ("net/tcp: Add TCP_AO_REPAIR")
Fixes: 3e643e4efa ("Bluetooth: Improve setsockopt() handling of malformed user input")
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: Francesco Ruggeri <fruggeri@arista.com>
Cc: Salam Noureddine <noureddine@arista.com>
Cc: David Ahern <dsahern@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Michal Luczaj <mhal@rbox.co>
Cc: David Wei <dw@davidwei.uk>
Cc: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Cc: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Simon Horman <horms@kernel.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Christian Brauner <brauner@kernel.org>
CC: Kees Cook <keescook@chromium.org>
Cc: netdev@vger.kernel.org
Cc: linux-bluetooth@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Link: https://patch.msgid.link/cfaedbc33ae9d36adaabf04fa79424f30ff1efdd.1775576651.git.metze@samba.org
Reviewed-by: Aleksa Sarai <aleksa@amutable.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

include/linux/sockptr.h

@@ -91,7 +91,7 @@ static inline int copy_struct_from_sockptr(void *dst, size_t ksize,
 	size_t rest = max(ksize, usize) - size;
 
 	if (!sockptr_is_kernel(src))
-		return copy_struct_from_user(dst, ksize, src.user, size);
+		return copy_struct_from_user(dst, ksize, src.user, usize);
 
 	if (usize < ksize) {
 		memset(dst + size, 0, rest);