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 X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT 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 110B1C04A6B for ; Fri, 10 May 2019 10:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB2DA217D7 for ; Fri, 10 May 2019 10:50:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=brauner.io header.i=@brauner.io header.b="GlZI7T1W" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727393AbfEJKuw (ORCPT ); Fri, 10 May 2019 06:50:52 -0400 Received: from mail-ed1-f68.google.com ([209.85.208.68]:41765 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727049AbfEJKuv (ORCPT ); Fri, 10 May 2019 06:50:51 -0400 Received: by mail-ed1-f68.google.com with SMTP id m4so4719993edd.8 for ; Fri, 10 May 2019 03:50:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=brauner.io; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=yBUeJbZyUrlht1SFBwi6imTZ/NYy8ameJGgWrSP1vis=; b=GlZI7T1WnjFL/pCE6RL90JiD3HomfRyuzRWfXP8khwqfvE1O6jQ0EJT7SLdL1uV/NR XQmpo0W9B9YA0jvl4Yac4pBrlmAo4bPEhoSFOasnOgaegfebiqLi//LpoHp6KpdEtzbT SlkXhMj6zigiMw8w1+kEGXBDwLSrVLL3YhvmRoIXIqd/3Au14Kq78BtvSre3p+lEoyKJ 8YBhMKSqHIt0xrhsePlpnvDjL/w8ChHGEk7h7nEJe8URf3Th+c2dgzNSOSFQvMMmouwH Pgo7GDsXGiQG5fp4yGsSTdpqUvc4Yrw6KcO+8UL15xOuWaCu/k3BZB/bU7JHtJJ83cXI eUhw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=yBUeJbZyUrlht1SFBwi6imTZ/NYy8ameJGgWrSP1vis=; b=hz4hrqJNEE05E0iqnYYllLhtOVGT6hF1PrikGBerSHhUoOyYEzskFuN3F7kqErxUTz EZUJpH+lHymXdBoyGgFn/Vrx5HxiAPPNFp9qSClCCjxZCuqfRGTrizyKS813rVOa0gbi y+Vl5aQAxebgmJSnshDcrT09xVPoBHpZFR9G0Q5aVfJp32IZUGpm7p1da3MmtvaS5Dls 2RK4vMnB/R/Td9ZjdRY3jGT1vILp/5fgwS4dcFUDYkP4BgmhHOvwgw9TI9iPr95Pw/1Q KF2wbaON8T9hu/agdWmUi9bCuWAtEeR6cRcYKU4ktT1aJ9CaqvWLL/8uIUMSrbnixiBd p1lQ== X-Gm-Message-State: APjAAAVDByyaCirOAUq+ouvM2ZNElLsSQNHFpWBkgWKsFZQVUa+ZkO0U qBz2neuseKhrz8R17m4fBxegVg== X-Google-Smtp-Source: APXvYqx6c5SkAxkvR6E61Q2AtV20gSOHa2PQkwc1IXDfDbCR3sG9xcU6m4gnZhy4jJvHFeqqTuhIcw== X-Received: by 2002:a17:906:b789:: with SMTP id dt9mr7831653ejb.244.1557485448979; Fri, 10 May 2019 03:50:48 -0700 (PDT) Received: from brauner.io ([178.19.218.101]) by smtp.gmail.com with ESMTPSA id r18sm684027ejh.92.2019.05.10.03.50.47 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 10 May 2019 03:50:48 -0700 (PDT) Date: Fri, 10 May 2019 12:50:47 +0200 From: Christian Brauner To: jannh@google.com, oleg@redhat.com, viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, arnd@arndb.de, arunks@codeaurora.org, cyphar@cyphar.com, dhowells@redhat.com, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, keescook@chromium.org, luto@amacapital.net, luto@kernel.org, mhocko@suse.com, mingo@kernel.org, mtk.manpages@gmail.com, namit@vmware.com, peterz@infradead.org, riel@surriel.com, shakeelb@google.com, syzkaller-bugs@googlegroups.com, tglx@linutronix.de, wad@chromium.org, syzbot+3286e58549edc479faae@syzkaller.appspotmail.com Subject: Re: [PATCH] fork: do not release lock that wasn't taken Message-ID: <20190510105046.jdox22ytlhojw37q@brauner.io> References: <20190510104913.27143-1-christian@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190510104913.27143-1-christian@brauner.io> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 10, 2019 at 12:49:13PM +0200, Christian Brauner wrote: > Avoid calling cgroup_threadgroup_change_end() without having called > cgroup_threadgroup_change_begin() first. > > During process creation we need to check whether the cgroup we are in > allows us to fork. To perform this check the cgroup needs to guard itself > against threadgroup changes and takes a lock. > Prior to CLONE_PIDFD the cleanup target "bad_fork_free_pid" would also need > to call cgroup_threadgroup_change_end() because said lock had already been > taken. > However, this is not the case anymore with the addition of CLONE_PIDFD. We > are now allocating a pidfd before we check whether the cgroup we're in can > fork and thus prior to taking the lock. So when copy_process() fails at the > right step it would release a lock we haven't taken. > This bug is not even very subtle to be honest. It's just not very clear > from the naming of cgroup_threadgroup_change_{begin,end}() that a lock is > taken. > > Here's the relevant splat: > > entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139 > RIP: 0023:0xf7fec849 > Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90 > 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 > 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 > RSP: 002b:00000000ffed5a8c EFLAGS: 00000246 ORIG_RAX: 0000000000000078 > RAX: ffffffffffffffda RBX: 0000000000003ffc RCX: 0000000000000000 > RDX: 00000000200005c0 RSI: 0000000000000000 RDI: 0000000000000000 > RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > ------------[ cut here ]------------ > DEBUG_LOCKS_WARN_ON(depth <= 0) > WARNING: CPU: 1 PID: 7744 at kernel/locking/lockdep.c:4052 __lock_release > kernel/locking/lockdep.c:4052 [inline] > WARNING: CPU: 1 PID: 7744 at kernel/locking/lockdep.c:4052 > lock_release+0x667/0xa00 kernel/locking/lockdep.c:4321 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 1 PID: 7744 Comm: syz-executor007 Not tainted 5.1.0+ #4 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x172/0x1f0 lib/dump_stack.c:113 > panic+0x2cb/0x65c kernel/panic.c:214 > __warn.cold+0x20/0x45 kernel/panic.c:566 > report_bug+0x263/0x2b0 lib/bug.c:186 > fixup_bug arch/x86/kernel/traps.c:179 [inline] > fixup_bug arch/x86/kernel/traps.c:174 [inline] > do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272 > do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291 > invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:972 > RIP: 0010:__lock_release kernel/locking/lockdep.c:4052 [inline] > RIP: 0010:lock_release+0x667/0xa00 kernel/locking/lockdep.c:4321 > Code: 0f 85 a0 03 00 00 8b 35 77 66 08 08 85 f6 75 23 48 c7 c6 a0 55 6b 87 > 48 c7 c7 40 25 6b 87 4c 89 85 70 ff ff ff e8 b7 a9 eb ff <0f> 0b 4c 8b 85 > 70 ff ff ff 4c 89 ea 4c 89 e6 4c 89 c7 e8 52 63 ff > RSP: 0018:ffff888094117b48 EFLAGS: 00010086 > RAX: 0000000000000000 RBX: 1ffff11012822f6f RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffffffff815af236 RDI: ffffed1012822f5b > RBP: ffff888094117c00 R08: ffff888092bfc400 R09: fffffbfff113301d > R10: fffffbfff113301c R11: ffffffff889980e3 R12: ffffffff8a451df8 > R13: ffffffff8142e71f R14: ffffffff8a44cc80 R15: ffff888094117bd8 > percpu_up_read.constprop.0+0xcb/0x110 include/linux/percpu-rwsem.h:92 > cgroup_threadgroup_change_end include/linux/cgroup-defs.h:712 [inline] > copy_process.part.0+0x47ff/0x6710 kernel/fork.c:2222 > copy_process kernel/fork.c:1772 [inline] > _do_fork+0x25d/0xfd0 kernel/fork.c:2338 > __do_compat_sys_x86_clone arch/x86/ia32/sys_ia32.c:240 [inline] > __se_compat_sys_x86_clone arch/x86/ia32/sys_ia32.c:236 [inline] > __ia32_compat_sys_x86_clone+0xbc/0x140 arch/x86/ia32/sys_ia32.c:236 > do_syscall_32_irqs_on arch/x86/entry/common.c:334 [inline] > do_fast_syscall_32+0x281/0xd54 arch/x86/entry/common.c:405 > entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139 > RIP: 0023:0xf7fec849 > Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90 > 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 > 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 > RSP: 002b:00000000ffed5a8c EFLAGS: 00000246 ORIG_RAX: 0000000000000078 > RAX: ffffffffffffffda RBX: 0000000000003ffc RCX: 0000000000000000 > RDX: 00000000200005c0 RSI: 0000000000000000 RDI: 0000000000000000 > RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > Kernel Offset: disabled > Rebooting in 86400 seconds.. > > Reported-by: syzbot+3286e58549edc479faae@syzkaller.appspotmail.com > Fixes: b3e583825266 ("clone: add CLONE_PIDFD") > Signed-off-by: Christian Brauner Assuming we agree that this is correct I bundle this into my pidfd tree together with the pidfd-metadata fix for .gitignore that Linus pointed out beginning of this week and send pr later today. Christian > --- > kernel/fork.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 5359facf9867..737db1828437 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -2102,7 +2102,7 @@ static __latent_entropy struct task_struct *copy_process( > */ > retval = cgroup_can_fork(p); > if (retval) > - goto bad_fork_put_pidfd; > + goto bad_fork_cgroup_threadgroup_change_end; > > /* > * From this point on we must avoid any synchronous user-space > @@ -2217,11 +2217,12 @@ static __latent_entropy struct task_struct *copy_process( > spin_unlock(¤t->sighand->siglock); > write_unlock_irq(&tasklist_lock); > cgroup_cancel_fork(p); > +bad_fork_cgroup_threadgroup_change_end: > + cgroup_threadgroup_change_end(current); > bad_fork_put_pidfd: > if (clone_flags & CLONE_PIDFD) > ksys_close(pidfd); > bad_fork_free_pid: > - cgroup_threadgroup_change_end(current); > if (pid != &init_struct_pid) > free_pid(pid); > bad_fork_cleanup_thread: > -- > 2.21.0 >