binder: create node flag to request sender's security context

This change “binder: create node flag to request sender’s security context” in Linux kernel is authored by Todd Kjos <tkjos [at] android.com> on Mon Jan 14 09:10:21 2019 -0800.

binder: create node flag to request sender's security context

To allow servers to verify client identity, allow a node
flag to be set that causes the sender's security context
to be delivered with the transaction. The BR_TRANSACTION
command is extended in BR_TRANSACTION_SEC_CTX to
contain a pointer to the security context string.

Signed-off-by: Todd Kjos <tkjos@google.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit ec74136.

There are 125 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/android/binder.c            | 106 ++++++++++++++++++++++++++++--------
 include/uapi/linux/android/binder.h |  19 +++++++
 2 files changed, 102 insertions(+), 23 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index cdfc876..5f6ef5e 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -329,6 +329,8 @@ struct binder_error {
  *                        (invariant after initialized)
  * @min_priority:         minimum scheduling priority
  *                        (invariant after initialized)
+ * @txn_security_ctx:     require sender's security context
+ *                        (invariant after initialized)
  * @async_todo:           list of async work items
  *                        (protected by @proc->inner_lock)
  *
@@ -365,6 +367,7 @@ struct binder_node {
 		 * invariant after initialization
 		 */
 		u8 accept_fds:1;
+		u8 txn_security_ctx:1;
 		u8 min_priority;
 	};
 	bool has_async_transaction;
@@ -615,6 +618,7 @@ struct binder_transaction {
 	long	saved_priority;
 	kuid_t	sender_euid;
 	struct list_head fd_fixups;
+	binder_uintptr_t security_ctx;
 	/**
 	 * @lock:  protects @from, @to_proc, and @to_thread
 	 *
@@ -1152,6 +1156,7 @@ static struct binder_node *binder_init_node_ilocked(
 	node->work.type = BINDER_WORK_NODE;
 	node->min_priority = flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
 	node->accept_fds = !!(flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
+	node->txn_security_ctx = !!(flags & FLAT_BINDER_FLAG_TXN_SECURITY_CTX);
 	spin_lock_init(&node->lock);
 	INIT_LIST_HEAD(&node->work.entry);
 	INIT_LIST_HEAD(&node->async_todo);
@@ -2778,6 +2783,8 @@ static void binder_transaction(struct binder_proc *proc,
 	binder_size_t last_fixup_min_off = 0;
 	struct binder_context *context = proc->context;
 	int t_debug_id = atomic_inc_return(&binder_last_id);
+	char *secctx = NULL;
+	u32 secctx_sz = 0;
 
 	e = binder_transaction_log_add(&binder_transaction_log);
 	e->debug_id = t_debug_id;
@@ -3020,6 +3027,20 @@ static void binder_transaction(struct binder_proc *proc,
 	t->flags = tr->flags;
 	t->priority = task_nice(current);
 
+	if (target_node && target_node->txn_security_ctx) {
+		u32 secid;
+
+		security_task_getsecid(proc->tsk, &secid);
+		ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
+		if (ret) {
+			return_error = BR_FAILED_REPLY;
+			return_error_param = ret;
+			return_error_line = __LINE__;
+			goto err_get_secctx_failed;
+		}
+		extra_buffers_size += ALIGN(secctx_sz, sizeof(u64));
+	}
+
 	trace_binder_transaction(reply, t, target_node);
 
 	t->buffer = binder_alloc_new_buf(&target_proc->alloc, tr->data_size,
@@ -3036,6 +3057,19 @@ static void binder_transaction(struct binder_proc *proc,
 		t->buffer = NULL;
 		goto err_binder_alloc_buf_failed;
 	}
+	if (secctx) {
+		size_t buf_offset = ALIGN(tr->data_size, sizeof(void *)) +
+				    ALIGN(tr->offsets_size, sizeof(void *)) +
+				    ALIGN(extra_buffers_size, sizeof(void *)) -
+				    ALIGN(secctx_sz, sizeof(u64));
+		char *kptr = t->buffer->data + buf_offset;
+
+		t->security_ctx = (uintptr_t)kptr +
+		    binder_alloc_get_user_buffer_offset(&target_proc->alloc);
+		memcpy(kptr, secctx, secctx_sz);
+		security_release_secctx(secctx, secctx_sz);
+		secctx = NULL;
+	}
 	t->buffer->debug_id = t->debug_id;
 	t->buffer->transaction = t;
 	t->buffer->target_node = target_node;
@@ -3305,6 +3339,9 @@ static void binder_transaction(struct binder_proc *proc,
 	t->buffer->transaction = NULL;
 	binder_alloc_free_buf(&target_proc->alloc, t->buffer);
 err_binder_alloc_buf_failed:
+	if (secctx)
+		security_release_secctx(secctx, secctx_sz);
+err_get_secctx_failed:
 	kfree(tcomplete);
 	binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
 err_alloc_tcomplete_failed:
@@ -4036,11 +4073,13 @@ static int binder_thread_read(struct binder_proc *proc,
 
 	while (1) {
 		uint32_t cmd;
-		struct binder_transaction_data tr;
+		struct binder_transaction_data_secctx tr;
+		struct binder_transaction_data *trd = &tr.transaction_data;
 		struct binder_work *w = NULL;
 		struct list_head *list = NULL;
 		struct binder_transaction *t = NULL;
 		struct binder_thread *t_from;
+		size_t trsize = sizeof(*trd);
 
 		binder_inner_proc_lock(proc);
 		if (!binder_worklist_empty_ilocked(&thread->todo))
@@ -4240,8 +4279,8 @@ static int binder_thread_read(struct binder_proc *proc,
 		if (t->buffer->target_node) {
 			struct binder_node *target_node = t->buffer->target_node;
 
-			tr.target.ptr = target_node->ptr;
-			tr.cookie =  target_node->cookie;
+			trd->target.ptr = target_node->ptr;
+			trd->cookie =  target_node->cookie;
 			t->saved_priority = task_nice(current);
 			if (t->priority < target_node->min_priority &&
 			    !(t->flags & TF_ONE_WAY))
@@ -4251,22 +4290,23 @@ static int binder_thread_read(struct binder_proc *proc,
 				binder_set_nice(target_node->min_priority);
 			cmd = BR_TRANSACTION;
 		} else {
-			tr.target.ptr = 0;
-			tr.cookie = 0;
+			trd->target.ptr = 0;
+			trd->cookie = 0;
 			cmd = BR_REPLY;
 		}
-		tr.code = t->code;
-		tr.flags = t->flags;
-		tr.sender_euid = from_kuid(current_user_ns(), t->sender_euid);
+		trd->code = t->code;
+		trd->flags = t->flags;
+		trd->sender_euid = from_kuid(current_user_ns(), t->sender_euid);
 
 		t_from = binder_get_txn_from(t);
 		if (t_from) {
 			struct task_struct *sender = t_from->proc->tsk;
 
-			tr.sender_pid = task_tgid_nr_ns(sender,
-							task_active_pid_ns(current));
+			trd->sender_pid =
+				task_tgid_nr_ns(sender,
+						task_active_pid_ns(current));
 		} else {
-			tr.sender_pid = 0;
+			trd->sender_pid = 0;
 		}
 
 		ret = binder_apply_fd_fixups(t);
@@ -4297,15 +4337,20 @@ static int binder_thread_read(struct binder_proc *proc,
 			}
 			continue;
 		}
-		tr.data_size = t->buffer->data_size;
-		tr.offsets_size = t->buffer->offsets_size;
-		tr.data.ptr.buffer = (binder_uintptr_t)
+		trd->data_size = t->buffer->data_size;
+		trd->offsets_size = t->buffer->offsets_size;
+		trd->data.ptr.buffer = (binder_uintptr_t)
 			((uintptr_t)t->buffer->data +
 			binder_alloc_get_user_buffer_offset(&proc->alloc));
-		tr.data.ptr.offsets = tr.data.ptr.buffer +
+		trd->data.ptr.offsets = trd->data.ptr.buffer +
 					ALIGN(t->buffer->data_size,
 					    sizeof(void *));
 
+		tr.secctx = t->security_ctx;
+		if (t->security_ctx) {
+			cmd = BR_TRANSACTION_SEC_CTX;
+			trsize = sizeof(tr);
+		}
 		if (put_user(cmd, (uint32_t __user *)ptr)) {
 			if (t_from)
 				binder_thread_dec_tmpref(t_from);
@@ -4316,7 +4361,7 @@ static int binder_thread_read(struct binder_proc *proc,
 			return -EFAULT;
 		}
 		ptr += sizeof(uint32_t);
-		if (copy_to_user(ptr, &tr, sizeof(tr))) {
+		if (copy_to_user(ptr, &tr, trsize)) {
 			if (t_from)
 				binder_thread_dec_tmpref(t_from);
 
@@ -4325,7 +4370,7 @@ static int binder_thread_read(struct binder_proc *proc,
 
 			return -EFAULT;
 		}
-		ptr += sizeof(tr);
+		ptr += trsize;
 
 		trace_binder_transaction_received(t);
 		binder_stat_br(proc, thread, cmd);
@@ -4333,16 +4378,18 @@ static int binder_thread_read(struct binder_proc *proc,
 			     "%d:%d %s %d %d:%d, cmd %d size %zd-%zd ptr %016llx-%016llxn",
 			     proc->pid, thread->pid,
 			     (cmd == BR_TRANSACTION) ? "BR_TRANSACTION" :
-			     "BR_REPLY",
+				(cmd == BR_TRANSACTION_SEC_CTX) ?
+				     "BR_TRANSACTION_SEC_CTX" : "BR_REPLY",
 			     t->debug_id, t_from ? t_from->proc->pid : 0,
 			     t_from ? t_from->pid : 0, cmd,
 			     t->buffer->data_size, t->buffer->offsets_size,
-			     (u64)tr.data.ptr.buffer, (u64)tr.data.ptr.offsets);
+			     (u64)trd->data.ptr.buffer,
+			     (u64)trd->data.ptr.offsets);
 
 		if (t_from)
 			binder_thread_dec_tmpref(t_from);
 		t->buffer->allow_user_free = 1;
-		if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
+		if (cmd != BR_REPLY && !(t->flags & TF_ONE_WAY)) {
 			binder_inner_proc_lock(thread->proc);
 			t->to_parent = thread->transaction_stack;
 			t->to_thread = thread;
@@ -4690,7 +4737,8 @@ static int binder_ioctl_write_read(struct file *filp,
 	return ret;
 }
 
-static int binder_ioctl_set_ctx_mgr(struct file *filp)
+static int binder_ioctl_set_ctx_mgr(struct file *filp,
+				    struct flat_binder_object *fbo)
 {
 	int ret = 0;
 	struct binder_proc *proc = filp->private_data;
@@ -4719,7 +4767,7 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
 	} else {
 		context->binder_context_mgr_uid = curr_euid;
 	}
-	new_node = binder_new_node(proc, NULL);
+	new_node = binder_new_node(proc, fbo);
 	if (!new_node) {
 		ret = -ENOMEM;
 		goto out;
@@ -4842,8 +4890,20 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		binder_inner_proc_unlock(proc);
 		break;
 	}
+	case BINDER_SET_CONTEXT_MGR_EXT: {
+		struct flat_binder_object fbo;
+
+		if (copy_from_user(&fbo, ubuf, sizeof(fbo))) {
+			ret = -EINVAL;
+			goto err;
+		}
+		ret = binder_ioctl_set_ctx_mgr(filp, &fbo);
+		if (ret)
+			goto err;
+		break;
+	}
 	case BINDER_SET_CONTEXT_MGR:
-		ret = binder_ioctl_set_ctx_mgr(filp);
+		ret = binder_ioctl_set_ctx_mgr(filp, NULL);
 		if (ret)
 			goto err;
 		break;
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index b9ba520..2832134 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -41,6 +41,14 @@ enum {
 enum {
 	FLAT_BINDER_FLAG_PRIORITY_MASK = 0xff,
 	FLAT_BINDER_FLAG_ACCEPTS_FDS = 0x100,
+
+	/**
+	 * @FLAT_BINDER_FLAG_TXN_SECURITY_CTX: request security contexts
+	 *
+	 * Only when set, causes senders to include their security
+	 * context
+	 */
+	FLAT_BINDER_FLAG_TXN_SECURITY_CTX = 0x1000,
 };
 
 #ifdef BINDER_IPC_32BIT
@@ -218,6 +226,7 @@ struct binder_node_info_for_ref {
 #define BINDER_VERSION			_IOWR('b', 9, struct binder_version)
 #define BINDER_GET_NODE_DEBUG_INFO	_IOWR('b', 11, struct binder_node_debug_info)
 #define BINDER_GET_NODE_INFO_FOR_REF	_IOWR('b', 12, struct binder_node_info_for_ref)
+#define BINDER_SET_CONTEXT_MGR_EXT	_IOW('b', 13, struct flat_binder_object)
 
 /*
  * NOTE: Two special error codes you should check for when calling
@@ -276,6 +285,11 @@ struct binder_transaction_data {
 	} data;
 };
 
+struct binder_transaction_data_secctx {
+	struct binder_transaction_data transaction_data;
+	binder_uintptr_t secctx;
+};
+
 struct binder_transaction_data_sg {
 	struct binder_transaction_data transaction_data;
 	binder_size_t buffers_size;
@@ -311,6 +325,11 @@ enum binder_driver_return_protocol {
 	BR_OK = _IO('r', 1),
 	/* No parameters! */
 
+	BR_TRANSACTION_SEC_CTX = _IOR('r', 2,
+				      struct binder_transaction_data_secctx),
+	/*
+	 * binder_transaction_data_secctx: the received command.
+	 */
 	BR_TRANSACTION = _IOR('r', 2, struct binder_transaction_data),
 	BR_REPLY = _IOR('r', 3, struct binder_transaction_data),
 	/*

The commit for this change in Linux stable tree is ec74136 (patch).

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