binder: Add support for file-descriptor arrays

This patch introduces a new binder_fd_array object,
that allows us to support one or more file descriptors
embedded in a buffer that is scatter-gathered.

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Martijn Coenen <[e-mail]>
Cc: Arve Hjønnevåg <[e-mail]>
Cc: Amit Pundir <[e-mail]>
Cc: Serban Constantinescu <[e-mail]>
Cc: Dmitry Shmidt <[e-mail]>
Cc: Rom Lemarchand <[e-mail]>
Cc: Android Kernel Team <[e-mail]>
Signed-off-by: Martijn Coenen <[e-mail]>
Signed-off-by: John Stultz <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/android/binder.c

···
 #define to_binder_buffer_object(hdr) \
 	container_of(hdr, struct binder_buffer_object, hdr)
 
+#define to_binder_fd_array_object(hdr) \
+	container_of(hdr, struct binder_fd_array_object, hdr)
+
 enum binder_stat_types {
 	BINDER_STAT_PROC,
 	BINDER_STAT_THREAD,
···
 	case BINDER_TYPE_PTR:
 		object_size = sizeof(struct binder_buffer_object);
 		break;
+	case BINDER_TYPE_FDA:
+		object_size = sizeof(struct binder_fd_array_object);
+		break;
 	default:
 		return 0;
 	}
···
 			 * transaction buffer gets freed
 			 */
 			break;
+		case BINDER_TYPE_FDA: {
+			struct binder_fd_array_object *fda;
+			struct binder_buffer_object *parent;
+			uintptr_t parent_buffer;
+			u32 *fd_array;
+			size_t fd_index;
+			binder_size_t fd_buf_size;
+
+			fda = to_binder_fd_array_object(hdr);
+			parent = binder_validate_ptr(buffer, fda->parent,
+						     off_start,
+						     offp - off_start);
+			if (!parent) {
+				pr_err("transaction release %d bad parent offset",
+				       debug_id);
+				continue;
+			}
+			/*
+			 * Since the parent was already fixed up, convert it
+			 * back to kernel address space to access it
+			 */
+			parent_buffer = parent->buffer -
+				proc->user_buffer_offset;
+
+			fd_buf_size = sizeof(u32) * fda->num_fds;
+			if (fda->num_fds >= SIZE_MAX / sizeof(u32)) {
+				pr_err("transaction release %d invalid number of fds (%lld)\n",
+				       debug_id, (u64)fda->num_fds);
+				continue;
+			}
+			if (fd_buf_size > parent->length ||
+			    fda->parent_offset > parent->length - fd_buf_size) {
+				/* No space for all file descriptors here. */
+				pr_err("transaction release %d not enough space for %lld fds in buffer\n",
+				       debug_id, (u64)fda->num_fds);
+				continue;
+			}
+			fd_array = (u32 *)(parent_buffer + fda->parent_offset);
+			for (fd_index = 0; fd_index < fda->num_fds; fd_index++)
+				task_close_fd(proc, fd_array[fd_index]);
+		} break;
 		default:
 			pr_err("transaction release %d bad object type %x\n",
 				debug_id, hdr->type);
···
 err_fget:
 err_fd_not_accepted:
 	return ret;
+}
+
+static int binder_translate_fd_array(struct binder_fd_array_object *fda,
+				     struct binder_buffer_object *parent,
+				     struct binder_transaction *t,
+				     struct binder_thread *thread,
+				     struct binder_transaction *in_reply_to)
+{
+	binder_size_t fdi, fd_buf_size, num_installed_fds;
+	int target_fd;
+	uintptr_t parent_buffer;
+	u32 *fd_array;
+	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)) {
+		binder_user_error("%d:%d got transaction with invalid number of fds (%lld)\n",
+				  proc->pid, thread->pid, (u64)fda->num_fds);
+		return -EINVAL;
+	}
+	if (fd_buf_size > parent->length ||
+	    fda->parent_offset > parent->length - fd_buf_size) {
+		/* No space for all file descriptors here. */
+		binder_user_error("%d:%d not enough space to store %lld fds in buffer\n",
+				  proc->pid, thread->pid, (u64)fda->num_fds);
+		return -EINVAL;
+	}
+	/*
+	 * Since the parent was already fixed up, convert it
+	 * back to the kernel address space to access it
+	 */
+	parent_buffer = parent->buffer - target_proc->user_buffer_offset;
+	fd_array = (u32 *)(parent_buffer + fda->parent_offset);
+	if (!IS_ALIGNED((unsigned long)fd_array, sizeof(u32))) {
+		binder_user_error("%d:%d parent offset not aligned correctly.\n",
+				  proc->pid, thread->pid);
+		return -EINVAL;
+	}
+	for (fdi = 0; fdi < fda->num_fds; fdi++) {
+		target_fd = binder_translate_fd(fd_array[fdi], t, thread,
+						in_reply_to);
+		if (target_fd < 0)
+			goto err_translate_fd_failed;
+		fd_array[fdi] = target_fd;
+	}
+	return 0;
+
+err_translate_fd_failed:
+	/*
+	 * Failed to allocate fd or security error, free fds
+	 * installed so far.
+	 */
+	num_installed_fds = fdi;
+	for (fdi = 0; fdi < num_installed_fds; fdi++)
+		task_close_fd(target_proc, fd_array[fdi]);
+	return target_fd;
 }
 
 static int binder_fixup_parent(struct binder_transaction *t,
···
 			fp->pad_binder = 0;
 			fp->fd = target_fd;
 		} break;
+		case BINDER_TYPE_FDA: {
+			struct binder_fd_array_object *fda =
+				to_binder_fd_array_object(hdr);
+			struct binder_buffer_object *parent =
+				binder_validate_ptr(t->buffer, fda->parent,
+						    off_start,
+						    offp - off_start);
+			if (!parent) {
+				binder_user_error("%d:%d got transaction with invalid parent offset or type\n",
+						  proc->pid, thread->pid);
+				return_error = BR_FAILED_REPLY;
+				goto err_bad_parent;
+			}
+			if (!binder_validate_fixup(t->buffer, off_start,
+						   parent, fda->parent_offset,
+						   last_fixup_obj,
+						   last_fixup_min_off)) {
+				binder_user_error("%d:%d got transaction with out-of-order buffer fixup\n",
+						  proc->pid, thread->pid);
+				return_error = BR_FAILED_REPLY;
+				goto err_bad_parent;
+			}
+			ret = binder_translate_fd_array(fda, parent, t, thread,
+							in_reply_to);
+			if (ret < 0) {
+				return_error = BR_FAILED_REPLY;
+				goto err_translate_failed;
+			}
+			last_fixup_obj = parent;
+			last_fixup_min_off =
+				fda->parent_offset + sizeof(u32) * fda->num_fds;
+		} break;
 		case BINDER_TYPE_PTR: {
 			struct binder_buffer_object *bp =
 				to_binder_buffer_object(hdr);
···
 err_translate_failed:
 err_bad_object_type:
 err_bad_offset:
+err_bad_parent:
 err_copy_data_failed:
 	trace_binder_transaction_failed_buffer_release(t->buffer);
 	binder_transaction_buffer_release(target_proc, t->buffer, offp);

include/uapi/linux/android/binder.h

···
 	BINDER_TYPE_HANDLE	= B_PACK_CHARS('s', 'h', '*', B_TYPE_LARGE),
 	BINDER_TYPE_WEAK_HANDLE	= B_PACK_CHARS('w', 'h', '*', B_TYPE_LARGE),
 	BINDER_TYPE_FD		= B_PACK_CHARS('f', 'd', '*', B_TYPE_LARGE),
+	BINDER_TYPE_FDA		= B_PACK_CHARS('f', 'd', 'a', B_TYPE_LARGE),
 	BINDER_TYPE_PTR		= B_PACK_CHARS('p', 't', '*', B_TYPE_LARGE),
 };
 
···
 
 enum {
 	BINDER_BUFFER_FLAG_HAS_PARENT = 0x01,
+};
+
+/* struct binder_fd_array_object - object describing an array of fds in a buffer
+ * @hdr:		common header structure
+ * @num_fds:		number of file descriptors in the buffer
+ * @parent:		index in offset array to buffer holding the fd array
+ * @parent_offset:	start offset of fd array in the buffer
+ *
+ * A binder_fd_array object represents an array of file
+ * descriptors embedded in a binder_buffer_object. It is
+ * different from a regular binder_buffer_object because it
+ * describes a list of file descriptors to fix up, not an opaque
+ * blob of memory, and hence the kernel needs to treat it differently.
+ *
+ * An example of how this would be used is with Android's
+ * native_handle_t object, which is a struct with a list of integers
+ * and a list of file descriptors. The native_handle_t struct itself
+ * will be represented by a struct binder_buffer_objct, whereas the
+ * embedded list of file descriptors is represented by a
+ * struct binder_fd_array_object with that binder_buffer_object as
+ * a parent.
+ */
+struct binder_fd_array_object {
+	struct binder_object_header	hdr;
+	binder_size_t			num_fds;
+	binder_size_t			parent;
+	binder_size_t			parent_offset;
 };
 
 /*