binder: fix incorrect calculation for num_valid

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: c12ae700d42e ("binder: use userspace pointer as base of buffer space")
Signed-off-by: Todd Kjos <tkjos@google.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191213202531.55010-1-tkjos@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index e9bc9fcc7ea5cb8213fdf73bc855b86f2c947341..b2dad43dbf82962b76c47c0a87d44bd15541e1de 100644 (file)
--- 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,