From mboxrd@z Thu Jan 1 00:00:00 1970 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 48929C433FE for ; Tue, 8 Nov 2022 13:57:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234770AbiKHN5z (ORCPT ); Tue, 8 Nov 2022 08:57:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234305AbiKHN5y (ORCPT ); Tue, 8 Nov 2022 08:57:54 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADF1860EB1 for ; Tue, 8 Nov 2022 05:57:53 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6DEA8B816DD for ; Tue, 8 Nov 2022 13:57:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9301DC433D6; Tue, 8 Nov 2022 13:57:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1667915871; bh=ACQcIMZT9yIl/kr96IyqLQTV/N7asKEOLVM0IcDc3Ys=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=zyQYXkKofrAjulfqqx3GTQ+1kXHsUzh8Gpi9RDQARTHhUEw4UU4XNd2dcP0ZZXQmz xP84gv5r5afnfUgCpx5uMErVnta8YNQZlQJb4IT6eVSS2RwLC3iCfnP4HV7/dY3xkU PJboGmHVPbrI+HTpUMFCYJcEgZ9V1rc41hzB2a+0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jann Horn , Minchan Kim , Yang Shi , Liam Howlett , Carlos Llamas , Todd Kjos Subject: [PATCH 5.10 086/118] binder: fix UAF of alloc->vma in race with munmap() Date: Tue, 8 Nov 2022 14:39:24 +0100 Message-Id: <20221108133344.451318926@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221108133340.718216105@linuxfoundation.org> References: <20221108133340.718216105@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Carlos Llamas In commit 720c24192404 ("ANDROID: binder: change down_write to down_read") binder assumed the mmap read lock is sufficient to protect alloc->vma inside binder_update_page_range(). This used to be accurate until commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap"), which now downgrades the mmap_lock after detaching the vma from the rbtree in munmap(). Then it proceeds to teardown and free the vma with only the read lock held. This means that accesses to alloc->vma in binder_update_page_range() now will race with vm_area_free() in munmap() and can cause a UAF as shown in the following KASAN trace: ================================================================== BUG: KASAN: use-after-free in vm_insert_page+0x7c/0x1f0 Read of size 8 at addr ffff16204ad00600 by task server/558 CPU: 3 PID: 558 Comm: server Not tainted 5.10.150-00001-gdc8dcf942daa #1 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x2a0 show_stack+0x18/0x2c dump_stack+0xf8/0x164 print_address_description.constprop.0+0x9c/0x538 kasan_report+0x120/0x200 __asan_load8+0xa0/0xc4 vm_insert_page+0x7c/0x1f0 binder_update_page_range+0x278/0x50c binder_alloc_new_buf+0x3f0/0xba0 binder_transaction+0x64c/0x3040 binder_thread_write+0x924/0x2020 binder_ioctl+0x1610/0x2e5c __arm64_sys_ioctl+0xd4/0x120 el0_svc_common.constprop.0+0xac/0x270 do_el0_svc+0x38/0xa0 el0_svc+0x1c/0x2c el0_sync_handler+0xe8/0x114 el0_sync+0x180/0x1c0 Allocated by task 559: kasan_save_stack+0x38/0x6c __kasan_kmalloc.constprop.0+0xe4/0xf0 kasan_slab_alloc+0x18/0x2c kmem_cache_alloc+0x1b0/0x2d0 vm_area_alloc+0x28/0x94 mmap_region+0x378/0x920 do_mmap+0x3f0/0x600 vm_mmap_pgoff+0x150/0x17c ksys_mmap_pgoff+0x284/0x2dc __arm64_sys_mmap+0x84/0xa4 el0_svc_common.constprop.0+0xac/0x270 do_el0_svc+0x38/0xa0 el0_svc+0x1c/0x2c el0_sync_handler+0xe8/0x114 el0_sync+0x180/0x1c0 Freed by task 560: kasan_save_stack+0x38/0x6c kasan_set_track+0x28/0x40 kasan_set_free_info+0x24/0x4c __kasan_slab_free+0x100/0x164 kasan_slab_free+0x14/0x20 kmem_cache_free+0xc4/0x34c vm_area_free+0x1c/0x2c remove_vma+0x7c/0x94 __do_munmap+0x358/0x710 __vm_munmap+0xbc/0x130 __arm64_sys_munmap+0x4c/0x64 el0_svc_common.constprop.0+0xac/0x270 do_el0_svc+0x38/0xa0 el0_svc+0x1c/0x2c el0_sync_handler+0xe8/0x114 el0_sync+0x180/0x1c0 [...] ================================================================== To prevent the race above, revert back to taking the mmap write lock inside binder_update_page_range(). One might expect an increase of mmap lock contention. However, binder already serializes these calls via top level alloc->mutex. Also, there was no performance impact shown when running the binder benchmark tests. Note this patch is specific to stable branches 5.4 and 5.10. Since in newer kernel releases binder no longer caches a pointer to the vma. Instead, it has been refactored to use vma_lookup() which avoids the issue described here. This switch was introduced in commit a43cfc87caaf ("android: binder: stop saving a pointer to the VMA"). Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Reported-by: Jann Horn Cc: # 5.10.x Cc: Minchan Kim Cc: Yang Shi Cc: Liam Howlett Signed-off-by: Carlos Llamas Acked-by: Todd Kjos Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder_alloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -212,7 +212,7 @@ static int binder_update_page_range(stru mm = alloc->vma_vm_mm; if (mm) { - mmap_read_lock(mm); + mmap_write_lock(mm); vma = alloc->vma; } @@ -270,7 +270,7 @@ static int binder_update_page_range(stru trace_binder_alloc_page_end(alloc, index); } if (mm) { - mmap_read_unlock(mm); + mmap_write_unlock(mm); mmput(mm); } return 0; @@ -303,7 +303,7 @@ err_page_ptr_cleared: } err_no_vma: if (mm) { - mmap_read_unlock(mm); + mmap_write_unlock(mm); mmput(mm); } return vma ? -ENOMEM : -ESRCH;