binder: read pre-translated fds from sender buffer

This patch is to prepare for an up coming patch where we read
pre-translated fds from the sender buffer and translate them before
copying them to the target.  It does not change run time.

The patch adds two new parameters to binder_translate_fd_array() to
hold the sender buffer and sender buffer parent.  These parameters let
us call copy_from_user() directly from the sender instead of using
binder_alloc_copy_from_buffer() to copy from the target.  Also the patch
adds some new alignment checks.  Previously the alignment checks would
have been done in a different place, but this lets us print more
useful error messages.
Reviewed-by: NMartijn Coenen <maco@android.com>
Acked-by: NChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: NTodd Kjos <tkjos@google.com>
Link: https://lore.kernel.org/r/20211130185152.437403-4-tkjos@google.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder.c

@@ -2234,15 +2234,17 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset,
 }
 
 static int binder_translate_fd_array(struct binder_fd_array_object *fda,
+				     const void __user *sender_ubuffer,
 				     struct binder_buffer_object *parent,
+				     struct binder_buffer_object *sender_uparent,
 				     struct binder_transaction *t,
 				     struct binder_thread *thread,
 				     struct binder_transaction *in_reply_to)
 {
 	binder_size_t fdi, fd_buf_size;
 	binder_size_t fda_offset;
+	const void __user *sender_ufda_base;
 	struct binder_proc *proc = thread->proc;
-	struct binder_proc *target_proc = t->to_proc;
 
 	fd_buf_size = sizeof(u32) * fda->num_fds;
 	if (fda->num_fds >= SIZE_MAX / sizeof(u32)) {
@@ -2266,7 +2268,10 @@ static int binder_translate_fd_array(struct binder_fd_array_object *fda,
 	 */
 	fda_offset = (parent->buffer - (uintptr_t)t->buffer->user_data) +
 		fda->parent_offset;
-	if (!IS_ALIGNED((unsigned long)fda_offset, sizeof(u32))) {
+	sender_ufda_base = (void __user *)sender_uparent->buffer + fda->parent_offset;
+
+	if (!IS_ALIGNED((unsigned long)fda_offset, sizeof(u32)) ||
+	    !IS_ALIGNED((unsigned long)sender_ufda_base, sizeof(u32))) {
 		binder_user_error("%d:%d parent offset not aligned correctly.\n",
 				  proc->pid, thread->pid);
 		return -EINVAL;
@@ -2275,10 +2280,9 @@ static int binder_translate_fd_array(struct binder_fd_array_object *fda,
 		u32 fd;
 		int ret;
 		binder_size_t offset = fda_offset + fdi * sizeof(fd);
+		binder_size_t sender_uoffset = fdi * sizeof(fd);
 
-		ret = binder_alloc_copy_from_buffer(&target_proc->alloc,
-						    &fd, t->buffer,
-						    offset, sizeof(fd));
+		ret = copy_from_user(&fd, sender_ufda_base + sender_uoffset, sizeof(fd));
 		if (!ret)
 			ret = binder_translate_fd(fd, offset, t, thread,
 						  in_reply_to);
@@ -2951,6 +2955,8 @@ static void binder_transaction(struct binder_proc *proc,
 		case BINDER_TYPE_FDA: {
 			struct binder_object ptr_object;
 			binder_size_t parent_offset;
+			struct binder_object user_object;
+			size_t user_parent_size;
 			struct binder_fd_array_object *fda =
 				to_binder_fd_array_object(hdr);
 			size_t num_valid = (buffer_offset - off_start_offset) /
@@ -2982,8 +2988,27 @@ static void binder_transaction(struct binder_proc *proc,
 				return_error_line = __LINE__;
 				goto err_bad_parent;
 			}
-			ret = binder_translate_fd_array(fda, parent, t, thread,
-							in_reply_to);
+			/*
+			 * We need to read the user version of the parent
+			 * object to get the original user offset
+			 */
+			user_parent_size =
+				binder_get_object(proc, user_buffer, t->buffer,
+						  parent_offset, &user_object);
+			if (user_parent_size != sizeof(user_object.bbo)) {
+				binder_user_error("%d:%d invalid ptr object size: %zd vs %zd\n",
+						  proc->pid, thread->pid,
+						  user_parent_size,
+						  sizeof(user_object.bbo));
+				return_error = BR_FAILED_REPLY;
+				return_error_param = -EINVAL;
+				return_error_line = __LINE__;
+				goto err_bad_parent;
+			}
+			ret = binder_translate_fd_array(fda, user_buffer,
+							parent,
+							&user_object.bbo, t,
+							thread, in_reply_to);
 			if (!ret)
 				ret = binder_alloc_copy_to_buffer(&target_proc->alloc,
 								  t->buffer,