linux-kernel - [PATCH 3.12 014/127] ANDROID: binder: Add strong ref checks

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Date:   Fri, 25 Nov 2016 09:28:47 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Arve Hjønnevåg <arve@...roid.com>,
        Martijn Coenen <maco@...roid.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 014/127] ANDROID: binder: Add strong ref checks

From: Arve Hjønnevåg <arve@...roid.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 0a3ffab93fe52530602fe47cd74802cffdb19c05 upstream.

Prevent using a binder_ref with only weak references where a strong
reference is required.

Signed-off-by: Arve Hjønnevåg <arve@...roid.com>
Signed-off-by: Martijn Coenen <maco@...roid.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/staging/android/binder.c | 30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c
index 69fd236345cb..8a436dae9b77 100644
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -994,7 +994,7 @@ static int binder_dec_node(struct binder_node *node, int strong, int internal)
 
 
 static struct binder_ref *binder_get_ref(struct binder_proc *proc,
-					 uint32_t desc)
+					 u32 desc, bool need_strong_ref)
 {
 	struct rb_node *n = proc->refs_by_desc.rb_node;
 	struct binder_ref *ref;
@@ -1002,12 +1002,16 @@ static struct binder_ref *binder_get_ref(struct binder_proc *proc,
 	while (n) {
 		ref = rb_entry(n, struct binder_ref, rb_node_desc);
 
-		if (desc < ref->desc)
+		if (desc < ref->desc) {
 			n = n->rb_left;
-		else if (desc > ref->desc)
+		} else if (desc > ref->desc) {
 			n = n->rb_right;
-		else
+		} else if (need_strong_ref && !ref->strong) {
+			binder_user_error("tried to use weak ref as strong ref\n");
+			return NULL;
+		} else {
 			return ref;
+		}
 	}
 	return NULL;
 }
@@ -1270,7 +1274,10 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
 		} break;
 		case BINDER_TYPE_HANDLE:
 		case BINDER_TYPE_WEAK_HANDLE: {
-			struct binder_ref *ref = binder_get_ref(proc, fp->handle);
+			struct binder_ref *ref;
+
+			ref = binder_get_ref(proc, fp->handle,
+					     fp->type == BINDER_TYPE_HANDLE);
 			if (ref == NULL) {
 				pr_err("transaction release %d bad handle %d\n",
 				 debug_id, fp->handle);
@@ -1362,7 +1369,7 @@ static void binder_transaction(struct binder_proc *proc,
 	} else {
 		if (tr->target.handle) {
 			struct binder_ref *ref;
-			ref = binder_get_ref(proc, tr->target.handle);
+			ref = binder_get_ref(proc, tr->target.handle, true);
 			if (ref == NULL) {
 				binder_user_error("%d:%d got transaction to invalid handle\n",
 					proc->pid, thread->pid);
@@ -1546,7 +1553,10 @@ static void binder_transaction(struct binder_proc *proc,
 		} break;
 		case BINDER_TYPE_HANDLE:
 		case BINDER_TYPE_WEAK_HANDLE: {
-			struct binder_ref *ref = binder_get_ref(proc, fp->handle);
+			struct binder_ref *ref;
+
+			ref = binder_get_ref(proc, fp->handle,
+					     fp->type == BINDER_TYPE_HANDLE);
 			if (ref == NULL) {
 				binder_user_error("%d:%d got transaction with invalid handle, %d\n",
 						proc->pid,
@@ -1739,7 +1749,9 @@ int binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
 						ref->desc);
 				}
 			} else
-				ref = binder_get_ref(proc, target);
+				ref = binder_get_ref(proc, target,
+						     cmd == BC_ACQUIRE ||
+						     cmd == BC_RELEASE);
 			if (ref == NULL) {
 				binder_user_error("%d:%d refcount change on invalid ref %d\n",
 					proc->pid, thread->pid, target);
@@ -1934,7 +1946,7 @@ int binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
 			if (get_user(cookie, (void __user * __user *)ptr))
 				return -EFAULT;
 			ptr += sizeof(void *);
-			ref = binder_get_ref(proc, target);
+			ref = binder_get_ref(proc, target, false);
 			if (ref == NULL) {
 				binder_user_error("%d:%d %s invalid ref %d\n",
 					proc->pid, thread->pid,
-- 
2.10.2