From patchwork Mon May 24 21:36:59 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 446836 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=ham 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 6596CC04FF3 for ; Mon, 24 May 2021 21:37:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F0DF61414 for ; Mon, 24 May 2021 21:37:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232744AbhEXVia (ORCPT ); Mon, 24 May 2021 17:38:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:45248 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232547AbhEXVi3 (ORCPT ); Mon, 24 May 2021 17:38:29 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id BD231613CC; Mon, 24 May 2021 21:36:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1621892220; bh=/tJMMQZqMEdrmOS4i1BEwq/ct3JbXy9Pl7/r35gLZ+g=; h=Date:From:To:Subject:From; b=OfzhlsTjMlQAgbpPDAPP0bvu2pSDM4Uvw1T7ndnJh49b3IQkAaMIBkpeCl0uVTEnw Dgcy1ziifYR0nQKxwOakh7w5y61B1hsRYeKHJb8EPAvPZewrZ11BnkAPgdf1N3vFN7 4CruRx3dCL6xT4gMkwzZmhK9gpevFXusOvoWhECw= Date: Mon, 24 May 2021 14:36:59 -0700 From: akpm@linux-foundation.org To: christian@brauner.io, clg@fr.ibm.com, ebiederm@xmission.com, keescook@chromium.org, mark.rutland@arm.com, mm-commits@vger.kernel.org, paulus@samba.org, schwidefsky@de.ibm.com, stable@vger.kernel.org Subject: + pid-take-a-reference-when-initializing-cad_pid.patch added to -mm tree Message-ID: <20210524213659.QN1DDYpOk%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: pid: take a reference when initializing `cad_pid` has been added to the -mm tree. Its filename is pid-take-a-reference-when-initializing-cad_pid.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/pid-take-a-reference-when-initializing-cad_pid.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/pid-take-a-reference-when-initializing-cad_pid.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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 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);