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Message-ID: <CAHC9VhS_Bfywhp+6H03bY7LrQsBz+io672pSS0DpiZKFiz4L6g@mail.gmail.com>
Date: Tue, 28 Jan 2020 08:39:00 -0500
From: Paul Moore <paul@...l-moore.com>
To: jeffv@...gle.com, omosnace@...hat.com,
Stephen Smalley <sds@...ho.nsa.gov>
Cc: Eric Paris <eparis@...isplace.org>, jannh@...gle.com,
keescook@...omium.org, linux-kernel@...r.kernel.org,
paulmck@...nel.org, selinux@...r.kernel.org,
syzkaller-bugs@...glegroups.com,
syzbot <syzbot+61cba5033e2072d61806@...kaller.appspotmail.com>
Subject: Re: possible deadlock in sidtab_sid2str_put
On Tue, Jan 28, 2020 at 7:50 AM syzbot
<syzbot+61cba5033e2072d61806@...kaller.appspotmail.com> wrote:
>
> syzbot has found a reproducer for the following crash on:
>
> HEAD commit: b0be0eff Merge tag 'x86-pti-2020-01-28' of git://git.kerne..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1432aebee00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=9784e57c96a92f20
> dashboard link: https://syzkaller.appspot.com/bug?extid=61cba5033e2072d61806
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10088e95e00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13fa605ee00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+61cba5033e2072d61806@...kaller.appspotmail.com
>
> =====================================================
> WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
> 5.5.0-syzkaller #0 Not tainted
> -----------------------------------------------------
> syz-executor305/10624 [HC0[0]:SC0[2]:HE1:SE0] is trying to acquire:
> ffff888098c14098 (&(&s->cache_lock)->rlock){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
> ffff888098c14098 (&(&s->cache_lock)->rlock){+.+.}, at: sidtab_sid2str_put.part.0+0x36/0x880 security/selinux/ss/sidtab.c:533
>
> and this task is already holding:
> ffffffff89865770 (&(&nf_conntrack_locks[i])->rlock){+.-.}, at: spin_lock include/linux/spinlock.h:338 [inline]
> ffffffff89865770 (&(&nf_conntrack_locks[i])->rlock){+.-.}, at: nf_conntrack_lock+0x17/0x70 net/netfilter/nf_conntrack_core.c:91
> which would create a new lock dependency:
> (&(&nf_conntrack_locks[i])->rlock){+.-.} -> (&(&s->cache_lock)->rlock){+.+.}
>
> but this new dependency connects a SOFTIRQ-irq-safe lock:
> (&(&nf_conntrack_locks[i])->rlock){+.-.}
>
> ... which became SOFTIRQ-irq-safe at:
> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:338 [inline]
> nf_conntrack_lock+0x17/0x70 net/netfilter/nf_conntrack_core.c:91
...
> to a SOFTIRQ-irq-unsafe lock:
> (&(&s->cache_lock)->rlock){+.+.}
>
> ... which became SOFTIRQ-irq-unsafe at:
> ...
> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:338 [inline]
> sidtab_sid2str_put.part.0+0x36/0x880 security/selinux/ss/sidtab.c:533
> sidtab_sid2str_put+0xa0/0xc0 security/selinux/ss/sidtab.c:566
> sidtab_entry_to_string security/selinux/ss/services.c:1279 [inline]
> sidtab_entry_to_string+0xf2/0x110 security/selinux/ss/services.c:1266
> security_sid_to_context_core+0x2c6/0x3c0 security/selinux/ss/services.c:1361
> security_sid_to_context+0x34/0x40 security/selinux/ss/services.c:1384
> avc_audit_post_callback+0x102/0x790 security/selinux/avc.c:709
> common_lsm_audit+0x5ac/0x1e00 security/lsm_audit.c:466
> slow_avc_audit+0x16a/0x1f0 security/selinux/avc.c:782
> avc_audit security/selinux/include/avc.h:140 [inline]
> avc_has_perm+0x543/0x610 security/selinux/avc.c:1185
> inode_has_perm+0x1a8/0x230 security/selinux/hooks.c:1631
> selinux_mmap_file+0x10a/0x1d0 security/selinux/hooks.c:3701
> security_mmap_file+0xa4/0x1e0 security/security.c:1482
> vm_mmap_pgoff+0xf0/0x230 mm/util.c:502
...
> other info that might help us debug this:
>
> Possible interrupt unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&(&s->cache_lock)->rlock);
> local_irq_disable();
> lock(&(&nf_conntrack_locks[i])->rlock);
> lock(&(&s->cache_lock)->rlock);
> <Interrupt>
> lock(&(&nf_conntrack_locks[i])->rlock);
>
> *** DEADLOCK ***
>
> 4 locks held by syz-executor305/10624:
> #0: ffffffff8c1acc68 (&table[i].mutex){+.+.}, at: nfnl_lock net/netfilter/nfnetlink.c:62 [inline]
> #0: ffffffff8c1acc68 (&table[i].mutex){+.+.}, at: nfnetlink_rcv_msg+0x9ee/0xfb0 net/netfilter/nfnetlink.c:224
> #1: ffff8880836415d8 (nlk_cb_mutex-NETFILTER){+.+.}, at: netlink_dump+0xe7/0xfb0 net/netlink/af_netlink.c:2199
> #2: ffffffff89865770 (&(&nf_conntrack_locks[i])->rlock){+.-.}, at: spin_lock include/linux/spinlock.h:338 [inline]
> #2: ffffffff89865770 (&(&nf_conntrack_locks[i])->rlock){+.-.}, at: nf_conntrack_lock+0x17/0x70 net/netfilter/nf_conntrack_core.c:91
> #3: ffffffff8b7df008 (&selinux_ss.policy_rwlock){.+.?}, at: security_sid_to_context_core+0x1ca/0x3c0 security/selinux/ss/services.c:1344
I think this is going to be tricky to fix due to the differing
contexts from which sidtab_sid2str_put() may be called. We already
have a check for !in_task() in sidtab_sid2str_put(), do we want to add
a check for !in_serving_softirq() too?
--
paul moore
www.paul-moore.com
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