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 E99CEC433F5 for ; Sat, 8 Oct 2022 18:29:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231162AbiJHS3u (ORCPT ); Sat, 8 Oct 2022 14:29:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51692 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230424AbiJHS3q (ORCPT ); Sat, 8 Oct 2022 14:29:46 -0400 Received: from cae.in-ulm.de (cae.in-ulm.de [217.10.14.231]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6FE94D105 for ; Sat, 8 Oct 2022 11:29:41 -0700 (PDT) Received: by cae.in-ulm.de (Postfix, from userid 1000) id 4F4C414026A; Sat, 8 Oct 2022 20:29:40 +0200 (CEST) Date: Sat, 8 Oct 2022 20:29:40 +0200 From: "Christian A. Ehrhardt" To: Tejun Heo Cc: syzbot , gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Christian Brauner , Yosry Ahmed Subject: Re: [syzbot] general protection fault in kernfs_get_inode Message-ID: References: <000000000000385cbf05ea3f1862@google.com> <00000000000028a44005ea40352b@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi (from another Christian), On Fri, Oct 07, 2022 at 11:35:49AM -1000, Tejun Heo wrote: > (cc'ing Christian and quoting whole body) > > Christan, I can't repro it here but think what we need is sth like the > following. The problem is that cgroup_is_dead() check in the fork path isn't > enough as the perm check depends on cgrp->procs_file being available but > that is cleared while DYING before DEAD. So, depending on the timing, we can > end up trying to deref NULL pointer in may_write. > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 8ad2c267ff471..603b7167450a1 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -4934,6 +4934,10 @@ static int cgroup_may_write(const struct cgroup *cgrp, struct super_block *sb) > > lockdep_assert_held(&cgroup_mutex); > > + /*if @cgrp is being removed, procs_file may already be gone */ > + if (!cgrp->procs_file.kn) > + return -ENODEV; > + > inode = kernfs_get_inode(sb, cgrp->procs_file.kn); > if (!inode) > return -ENOMEM; I had syzbot hit the same crash here and as can be seen from the reproducer the root cause is that the target cgroup (specified via CLONE_INTO_CGROUP) is a version 1 cgroup. These cgroups just don't initialize ->procs_file.kn. This is a regression from v6.0 caused by f3a2aebdd6 ("cgroup: enable cgroup_get_from_file() on cgroup1") Unless we want to revert this patch the correct fix might be something like this: diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index f487c54a0087..67474b1ae087 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -6249,6 +6249,11 @@ static int cgroup_css_set_fork(struct kernel_clone_args *kargs) goto err; } + if (!cgroup_on_dfl(dst_cgrp)) { + ret = -EBADF; + goto err; + } + if (cgroup_is_dead(dst_cgrp)) { ret = -ENODEV; goto err; For reference: This is the reproducer produces by syzbot here: | r0 = fsopen(&(0x7f0000000040)='cpuset\x00', 0x0) | fsconfig$FSCONFIG_CMD_CREATE(r0, 0x6, 0x0, 0x0, 0x0) | r1 = fsmount(r0, 0x0, 0x0) | syz_clone3(&(0x7f00000009c0)={0x244000700, 0x0, 0x0, 0x0, {}, 0x0, 0x0, 0x0, 0x0, 0x0, {r1}}, 0x58) The crash is 100% reproducible on every single run, i.e. not a deletion race or similar. regards Christian > > > On Tue, Oct 04, 2022 at 07:19:34PM -0700, syzbot wrote: > > syzbot has found a reproducer for the following issue on: > > > > HEAD commit: 0326074ff465 Merge tag 'net-next-6.1' of git://git.kernel... > > git tree: upstream > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=149c92cc880000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=e1de7ca9efcc028c > > dashboard link: https://syzkaller.appspot.com/bug?extid=534ee3d24c37c411f37f > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10af2492880000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=104874f0880000 > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/43729d6ce2fc/disk-0326074f.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/1f76d6f68eb3/vmlinux-0326074f.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+534ee3d24c37c411f37f@syzkaller.appspotmail.com > > > > general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN > > KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097] > > CPU: 1 PID: 3617 Comm: syz-executor384 Not tainted 6.0.0-syzkaller-02734-g0326074ff465 #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022 > > RIP: 0010:kernfs_ino include/linux/kernfs.h:358 [inline] > > RIP: 0010:kernfs_get_inode+0x2e/0x520 fs/kernfs/inode.c:254 > > Code: 41 56 41 55 41 54 49 89 fc 53 48 89 f3 e8 1a 04 7e ff 48 8d bb 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 3a 04 00 00 48 8b b3 90 00 00 00 4c 89 e7 e8 79 > > RSP: 0018:ffffc90003c8fa30 EFLAGS: 00010206 > > RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 > > RDX: 0000000000000012 RSI: ffffffff81fd1156 RDI: 0000000000000090 > > RBP: ffffc90003c8fa50 R08: 0000000000000005 R09: 0000000000000000 > > R10: 0000000000000001 R11: 0000000000000024 R12: ffff8880224ba000 > > R13: ffff888075922000 R14: ffff88801ebf0000 R15: ffff8880211ae000 > > FS: 0000555556907300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000020000200 CR3: 000000001c179000 CR4: 00000000003506e0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > > > cgroup_may_write+0x86/0x120 kernel/cgroup/cgroup.c:4937 > > cgroup_css_set_fork kernel/cgroup/cgroup.c:6237 [inline] > > cgroup_can_fork+0x961/0xec0 kernel/cgroup/cgroup.c:6331 > > copy_process+0x43ed/0x7090 kernel/fork.c:2358 > > kernel_clone+0xe7/0xab0 kernel/fork.c:2671 > > __do_sys_clone3+0x1cd/0x2e0 kernel/fork.c:2963 > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > RIP: 0033:0x7f621d8c3e99 > > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 > > RSP: 002b:00007ffcaa952ec8 EFLAGS: 00000206 ORIG_RAX: 00000000000001b3 > > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f621d8c3e99 > > RDX: 0000000000000000 RSI: 0000000000000058 RDI: 00007ffcaa952f40 > > RBP: 0000000000000000 R08: 00007ffcaa952d60 R09: 00007ffcaa952ef0 > > R10: 00000000ffffffff R11: 0000000000000206 R12: 00007ffcaa952eec > > R13: 00007ffcaa952f00 R14: 00007ffcaa952f40 R15: 0000000000000000 > > > > Modules linked in: > > ---[ end trace 0000000000000000 ]--- > > RIP: 0010:kernfs_ino include/linux/kernfs.h:358 [inline] > > RIP: 0010:kernfs_get_inode+0x2e/0x520 fs/kernfs/inode.c:254 > > Code: 41 56 41 55 41 54 49 89 fc 53 48 89 f3 e8 1a 04 7e ff 48 8d bb 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 3a 04 00 00 48 8b b3 90 00 00 00 4c 89 e7 e8 79 > > RSP: 0018:ffffc90003c8fa30 EFLAGS: 00010206 > > RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 > > RDX: 0000000000000012 RSI: ffffffff81fd1156 RDI: 0000000000000090 > > RBP: ffffc90003c8fa50 R08: 0000000000000005 R09: 0000000000000000 > > R10: 0000000000000001 R11: 0000000000000024 R12: ffff8880224ba000 > > R13: ffff888075922000 R14: ffff88801ebf0000 R15: ffff8880211ae000 > > FS: 0000555556907300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 00007ffcaa9cb8f0 CR3: 000000001c179000 CR4: 00000000003506f0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > ---------------- > > Code disassembly (best guess): > > 0: 41 56 push %r14 > > 2: 41 55 push %r13 > > 4: 41 54 push %r12 > > 6: 49 89 fc mov %rdi,%r12 > > 9: 53 push %rbx > > a: 48 89 f3 mov %rsi,%rbx > > d: e8 1a 04 7e ff callq 0xff7e042c > > 12: 48 8d bb 90 00 00 00 lea 0x90(%rbx),%rdi > > 19: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax > > 20: fc ff df > > 23: 48 89 fa mov %rdi,%rdx > > 26: 48 c1 ea 03 shr $0x3,%rdx > > * 2a: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction > > 2e: 0f 85 3a 04 00 00 jne 0x46e > > 34: 48 8b b3 90 00 00 00 mov 0x90(%rbx),%rsi > > 3b: 4c 89 e7 mov %r12,%rdi > > 3e: e8 .byte 0xe8 > > 3f: 79 .byte 0x79 > > > > -- > tejun