From patchwork Sat Jun 5 03:01:14 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12301159 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69A11C4743D for ; Sat, 5 Jun 2021 06:07:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 176746120D for ; Sat, 5 Jun 2021 06:07:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 176746120D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AE2F36B0081; Sat, 5 Jun 2021 02:07:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A92606B0082; Sat, 5 Jun 2021 02:07:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 90BE06B0083; Sat, 5 Jun 2021 02:07:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0116.hostedemail.com [216.40.44.116]) by kanga.kvack.org (Postfix) with ESMTP id 51D6B6B0081 for ; Sat, 5 Jun 2021 02:07:19 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id EFC6298BA for ; Sat, 5 Jun 2021 06:07:18 +0000 (UTC) X-FDA: 78218637756.07.3EF86DC Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf03.hostedemail.com (Postfix) with ESMTP id 8EBCCC0A46BC for ; Sat, 5 Jun 2021 06:06:33 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 54C58613FE; Sat, 5 Jun 2021 03:01:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1622862075; bh=xN24bw5gXooEM2IRZG521MnKs5Y6w5rTkRSYc0gKwr8=; h=Date:From:To:Subject:In-Reply-To:From; b=c4ejkzgHkjOm8HkpHQssd90DIQFRsn4O2WO8hjj856f4VYaHuj9uypMh1GNvg1++O xniKHBRqoodTlgRNtDs3dTsO4A+Vejsf7l3VxcWS6+Pgg72jX82SqaPi8MmB5/wUHE /ytxKu1Jc2zatvZ0eMJrLF55+Yc23tF/pa7rmwZg= Date: Fri, 04 Jun 2021 20:01:14 -0700 From: Andrew Morton To: akpm@linux-foundation.org, christian.brauner@ubuntu.com, christian@brauner.io, clg@fr.ibm.com, ebiederm@xmission.com, keescook@chromium.org, linux-mm@kvack.org, mark.rutland@arm.com, mm-commits@vger.kernel.org, paulus@samba.org, schwidefsky@de.ibm.com, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 03/13] pid: take a reference when initializing `cad_pid` Message-ID: <20210605030114.E2boaQwOv%akpm@linux-foundation.org> In-Reply-To: <20210604200040.d8d0406caf195525620c0f3d@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 8EBCCC0A46BC Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=c4ejkzgH; dmarc=none; spf=pass (imf03.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Stat-Signature: h9k31641pfn98cpbdjdpustah3k9ihkx X-HE-Tag: 1622873193-108154 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Mark Rutland Subject: pid: take a reference when initializing `cad_pid` During boot, kernel_init_freeable() initializes `cad_pid` to the init task's struct pid. Later on, we may change `cad_pid` via a sysctl, and when this happens proc_do_cad_pid() will increment the refcount on the new pid via get_pid(), and will decrement the refcount on the old pid via put_pid(). As we never called get_pid() when we initialized `cad_pid`, we decrement a reference we never incremented, can therefore free the init task's struct pid early. As there can be dangling references to the struct pid, we can later encounter a use-after-free (e.g. when delivering signals). This was spotted when fuzzing v5.13-rc3 with Syzkaller, but seems to have been around since the conversion of `cad_pid` to struct pid in commit: 9ec52099e4b8678a ("[PATCH] replace cad_pid by a struct pid") ... from the pre-KASAN stone age of v2.6.19. Fix this by getting a reference to the init task's struct pid when we assign it to `cad_pid`. Full KASAN splat below. ================================================================== BUG: KASAN: use-after-free in ns_of_pid include/linux/pid.h:153 [inline] BUG: KASAN: use-after-free in task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509 Read of size 4 at addr ffff23794dda0004 by task syz-executor.0/273 CPU: 1 PID: 273 Comm: syz-executor.0 Not tainted 5.12.0-00001-g9aef892b2d15 #1 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x4a8 arch/arm64/kernel/stacktrace.c:105 show_stack+0x34/0x48 arch/arm64/kernel/stacktrace.c:191 __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x1d4/0x2a0 lib/dump_stack.c:120 print_address_description.constprop.11+0x60/0x3a8 mm/kasan/report.c:232 __kasan_report mm/kasan/report.c:399 [inline] kasan_report+0x1e8/0x200 mm/kasan/report.c:416 __asan_report_load4_noabort+0x30/0x48 mm/kasan/report_generic.c:308 ns_of_pid include/linux/pid.h:153 [inline] task_active_pid_ns+0xc0/0xc8 kernel/pid.c:509 do_notify_parent+0x308/0xe60 kernel/signal.c:1950 exit_notify kernel/exit.c:682 [inline] do_exit+0x2334/0x2bd0 kernel/exit.c:845 do_group_exit+0x108/0x2c8 kernel/exit.c:922 get_signal+0x4e4/0x2a88 kernel/signal.c:2781 do_signal arch/arm64/kernel/signal.c:882 [inline] do_notify_resume+0x300/0x970 arch/arm64/kernel/signal.c:936 work_pending+0xc/0x2dc Allocated by task 0: kasan_save_stack+0x28/0x58 mm/kasan/common.c:38 kasan_set_track mm/kasan/common.c:46 [inline] set_alloc_info mm/kasan/common.c:427 [inline] __kasan_slab_alloc+0x88/0xa8 mm/kasan/common.c:460 kasan_slab_alloc include/linux/kasan.h:223 [inline] slab_post_alloc_hook+0x50/0x5c0 mm/slab.h:516 slab_alloc_node mm/slub.c:2907 [inline] slab_alloc mm/slub.c:2915 [inline] kmem_cache_alloc+0x1f4/0x4c0 mm/slub.c:2920 alloc_pid+0xdc/0xc00 kernel/pid.c:180 copy_process+0x2794/0x5e18 kernel/fork.c:2129 kernel_clone+0x194/0x13c8 kernel/fork.c:2500 kernel_thread+0xd4/0x110 kernel/fork.c:2552 rest_init+0x44/0x4a0 init/main.c:687 arch_call_rest_init+0x1c/0x28 start_kernel+0x520/0x554 init/main.c:1064 0x0 Freed by task 270: kasan_save_stack+0x28/0x58 mm/kasan/common.c:38 kasan_set_track+0x28/0x40 mm/kasan/common.c:46 kasan_set_free_info+0x28/0x50 mm/kasan/generic.c:357 ____kasan_slab_free mm/kasan/common.c:360 [inline] ____kasan_slab_free mm/kasan/common.c:325 [inline] __kasan_slab_free+0xf4/0x148 mm/kasan/common.c:367 kasan_slab_free include/linux/kasan.h:199 [inline] slab_free_hook mm/slub.c:1562 [inline] slab_free_freelist_hook+0x98/0x260 mm/slub.c:1600 slab_free mm/slub.c:3161 [inline] kmem_cache_free+0x224/0x8e0 mm/slub.c:3177 put_pid.part.4+0xe0/0x1a8 kernel/pid.c:114 put_pid+0x30/0x48 kernel/pid.c:109 proc_do_cad_pid+0x190/0x1b0 kernel/sysctl.c:1401 proc_sys_call_handler+0x338/0x4b0 fs/proc/proc_sysctl.c:591 proc_sys_write+0x34/0x48 fs/proc/proc_sysctl.c:617 call_write_iter include/linux/fs.h:1977 [inline] new_sync_write+0x3ac/0x510 fs/read_write.c:518 vfs_write fs/read_write.c:605 [inline] vfs_write+0x9c4/0x1018 fs/read_write.c:585 ksys_write+0x124/0x240 fs/read_write.c:658 __do_sys_write fs/read_write.c:670 [inline] __se_sys_write fs/read_write.c:667 [inline] __arm64_sys_write+0x78/0xb0 fs/read_write.c:667 __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline] invoke_syscall arch/arm64/kernel/syscall.c:49 [inline] el0_svc_common.constprop.1+0x16c/0x388 arch/arm64/kernel/syscall.c:129 do_el0_svc+0xf8/0x150 arch/arm64/kernel/syscall.c:168 el0_svc+0x28/0x38 arch/arm64/kernel/entry-common.c:416 el0_sync_handler+0x134/0x180 arch/arm64/kernel/entry-common.c:432 el0_sync+0x154/0x180 arch/arm64/kernel/entry.S:701 The buggy address belongs to the object at ffff23794dda0000 which belongs to the cache pid of size 224 The buggy address is located 4 bytes inside of 224-byte region [ffff23794dda0000, ffff23794dda00e0) The buggy address belongs to the page: page:(____ptrval____) refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4dda0 head:(____ptrval____) order:1 compound_mapcount:0 flags: 0x3fffc0000010200(slab|head) raw: 03fffc0000010200 dead000000000100 dead000000000122 ffff23794d40d080 raw: 0000000000000000 0000000000190019 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff23794dd9ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff23794dd9ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff23794dda0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff23794dda0080: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc ffff23794dda0100: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00 ================================================================== Link: https://lkml.kernel.org/r/20210524172230.38715-1-mark.rutland@arm.com Fixes: 9ec52099e4b8678a ("[PATCH] replace cad_pid by a struct pid") Signed-off-by: Mark Rutland Acked-by: Christian Brauner Cc: Cedric Le Goater Cc: Christian Brauner Cc: Eric W. Biederman Cc: Kees Cook Cc: Paul Mackerras Cc: Signed-off-by: Andrew Morton --- init/main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/init/main.c~pid-take-a-reference-when-initializing-cad_pid +++ a/init/main.c @@ -1537,7 +1537,7 @@ static noinline void __init kernel_init_ */ set_mems_allowed(node_states[N_MEMORY]); - cad_pid = task_pid(current); + cad_pid = get_pid(task_pid(current)); smp_prepare_cpus(setup_max_cpus);