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From:   Todd Kjos <tkjos@android.com>
To:     tkjos@google.com, gregkh@linuxfoundation.org, arve@android.com,
        devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org,
        maco@google.com
Cc:     joel@joelfernandes.org, kernel-team@android.com
Subject: [PATCH] binder: fix incorrect calculation for num_valid
Date:   Fri, 13 Dec 2019 12:25:31 -0800
Message-Id: <20191213202531.55010-1-tkjos@google.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

For BINDER_TYPE_PTR and BINDER_TYPE_FDA transactions, the
num_valid local was calculated incorrectly causing the
range check in binder_validate_ptr() to miss out-of-bounds
offsets.

Fixes: bde4a19fc04f ("binder: use userspace pointer as base of buffer space")
Signed-off-by: Todd Kjos <tkjos@google.com>
---
 drivers/android/binder.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index e9bc9fcc7ea5..b2dad43dbf82 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3310,7 +3310,7 @@ static void binder_transaction(struct binder_proc *proc,
 			binder_size_t parent_offset;
 			struct binder_fd_array_object *fda =
 				to_binder_fd_array_object(hdr);
-			size_t num_valid = (buffer_offset - off_start_offset) *
+			size_t num_valid = (buffer_offset - off_start_offset) /
 						sizeof(binder_size_t);
 			struct binder_buffer_object *parent =
 				binder_validate_ptr(target_proc, t->buffer,
@@ -3384,7 +3384,7 @@ static void binder_transaction(struct binder_proc *proc,
 				t->buffer->user_data + sg_buf_offset;
 			sg_buf_offset += ALIGN(bp->length, sizeof(u64));
 
-			num_valid = (buffer_offset - off_start_offset) *
+			num_valid = (buffer_offset - off_start_offset) /
 					sizeof(binder_size_t);
 			ret = binder_fixup_parent(t, thread, bp,
 						  off_start_offset,
-- 
2.24.1.735.g03f4e72817-goog