net: fix compat pointer in get_compat_msghdr()

A previous change enabled external users to copy the data before
calling __get_compat_msghdr(), but didn't modify get_compat_msghdr() or
__io_compat_recvmsg_copy_hdr() to take that into account. They are both
stil passing in the __user pointer rather than the copied version.

Ensure we pass in the kernel struct, not the pointer to the user data.

Link: https://lore.kernel.org/all/46439555-644d-08a1-7d66-16f8f9a320f0@samsung.com/
Fixes: 1a3e4e94a1b9 ("net: copy from user before calling __get_compat_msghdr")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net.c

@@ -398,7 +398,7 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
 	if (copy_from_user(&msg, sr->umsg_compat, sizeof(msg)))
 		return -EFAULT;
 
-	ret = __get_compat_msghdr(&iomsg->msg, sr->umsg_compat, &iomsg->uaddr);
+	ret = __get_compat_msghdr(&iomsg->msg, &msg, &iomsg->uaddr);
 	if (ret)
 		return ret;
 

net/compat.c

@@ -89,7 +89,7 @@ int get_compat_msghdr(struct msghdr *kmsg,
 	if (copy_from_user(&msg, umsg, sizeof(*umsg)))
 		return -EFAULT;
 
-	err = __get_compat_msghdr(kmsg, umsg, save_addr);
+	err = __get_compat_msghdr(kmsg, &msg, save_addr);
 	if (err)
 		return err;