From nobody Fri Dec 19 00:21:38 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F3F6C4167B for ; Fri, 1 Dec 2023 17:22:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1378791AbjLARWn (ORCPT ); Fri, 1 Dec 2023 12:22:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58508 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230097AbjLARWe (ORCPT ); Fri, 1 Dec 2023 12:22:34 -0500 Received: from mail-pg1-x549.google.com (mail-pg1-x549.google.com [IPv6:2607:f8b0:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B5232D4A for ; Fri, 1 Dec 2023 09:22:40 -0800 (PST) Received: by mail-pg1-x549.google.com with SMTP id 41be03b00d2f7-5be10675134so806219a12.1 for ; Fri, 01 Dec 2023 09:22:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1701451360; x=1702056160; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=B/6Po4/tnNntaDAeP6ov7pxdzhgx9dRD0K+AuBuXOhY=; b=268Dr+wrvadvZwi8cLpjnW9opjet/sLNs2nmulFAaxIMtGkrEdRHHOkyuf6OaYfusB O73xjl5yRzV5J+dqi5bzFybdJQERX8+ek9LOue8xNq9TW5eoYluHNPetUNynP2GgfnKd 8OZs/jlfiTAlPn2wsDbRlBD5AlpjIU9WY/Ymub+b+W/BLQcxqSgpGvVEMAaOs5vhsYQ2 Rm9DxB1+9UKdFlqD5APNh4Ki4Id9EvclWYTXjlycPMkHmjLDSd8rbEeUqp+aGrUaa9XN cmfk4pCH93wFB2sfbCBCM9UGiv2k5ugZgFdDI/5Iyg9j0lb6YxmRAXwvkKVe1eVPGqKY XhUw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701451360; x=1702056160; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=B/6Po4/tnNntaDAeP6ov7pxdzhgx9dRD0K+AuBuXOhY=; b=FRqE9AxDo8TuuD6ZePn829Z2NyBes1Q28jephv7oAbOCHlsWEwnKUCkZnXNqUNN+jw nRQP3/mj2eGpOyqgdYfgzy0b0/palmhpS44xGstWr8fHd/d/SugmRT8HZ0LFdePnqqjD lYM/3RhUph2ZRDdtKdJ7DmQnNOYVXtjazaEecbrBJeysO6NQUpJPgD+xg34nNy3uslFf 9lH+F0RNp5AupfTvAfosRLrG6IlebJsCyOzxkYHsSDpH89otIHZ/zqIdze6f9ID0mAdz oHYMwDPL+GOv+5cXufcECcgBKiqGnb18NkKPsFGcKJogJ7Q9tuQt+vC1sDTRY5nJIBsn kxbQ== X-Gm-Message-State: AOJu0YzFmREjQD1ycPIf/d5tKN0SBuzOlZUf68rpfHWpabeb8OhyoohN RoKtYokq/zQlyGCeGqfiwuXzGoZTTmhKUw== X-Google-Smtp-Source: AGHT+IHWyvK3M0LsZmLaINPZeiMhROek+8yo/ObhMVkrkjJKvC7VWvikZ8pv3h03UnY8F3+XjwkMywJAdk2R5g== X-Received: from xllamas.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5070]) (user=cmllamas job=sendgmr) by 2002:a17:902:c40d:b0:1cf:8819:a986 with SMTP id k13-20020a170902c40d00b001cf8819a986mr5430784plk.8.1701451360090; Fri, 01 Dec 2023 09:22:40 -0800 (PST) Date: Fri, 1 Dec 2023 17:21:32 +0000 In-Reply-To: <20231201172212.1813387-1-cmllamas@google.com> Mime-Version: 1.0 References: <20231201172212.1813387-1-cmllamas@google.com> X-Mailer: git-send-email 2.43.0.rc2.451.g8631bc7472-goog Message-ID: <20231201172212.1813387-4-cmllamas@google.com> Subject: [PATCH v2 03/28] binder: fix race between mmput() and do_exit() From: Carlos Llamas To: Greg Kroah-Hartman , "=?UTF-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?=" , Todd Kjos , Martijn Coenen , Joel Fernandes , Christian Brauner , Carlos Llamas , Suren Baghdasaryan , Brian Swetland Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, Alice Ryhl , Greg Kroah-Hartman Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Task A calls binder_update_page_range() to allocate and insert pages on a remote address space from Task B. For this, Task A pins the remote mm via mmget_not_zero() first. This can race with Task B do_exit() and the final mmput() refcount decrement will come from Task A. Task A | Task B ------------------+------------------ mmget_not_zero() | | do_exit() | exit_mm() | mmput() mmput() | exit_mmap() | remove_vma() | fput() | In this case, the work of ____fput() from Task B is queued up in Task A as TWA_RESUME. So in theory, Task A returns to userspace and the cleanup work gets executed. However, Task A instead sleep, waiting for a reply from Task B that never comes (it's dead). This means the binder_deferred_release() is blocked until an unrelated binder event forces Task A to go back to userspace. All the associated death notifications will also be delayed until then. In order to fix this use mmput_async() that will schedule the work in the corresponding mm->async_put_work WQ instead of Task A. Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Reviewed-by: Alice Ryhl Signed-off-by: Carlos Llamas --- drivers/android/binder_alloc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 9d2eff70c3ba..adcec5ec0959 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -271,7 +271,7 @@ static int binder_update_page_range(struct binder_alloc= *alloc, int allocate, } if (mm) { mmap_write_unlock(mm); - mmput(mm); + mmput_async(mm); } return 0; =20 @@ -304,7 +304,7 @@ static int binder_update_page_range(struct binder_alloc= *alloc, int allocate, err_no_vma: if (mm) { mmap_write_unlock(mm); - mmput(mm); + mmput_async(mm); } return vma ? -ENOMEM : -ESRCH; } --=20 2.43.0.rc2.451.g8631bc7472-goog