From: Eric Biggers <ebiggers@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: aou@eecs.berkeley.edu,
syzbot <syzbot+6455648abc28dbdd1e7f@syzkaller.appspotmail.com>,
Palmer Dabbelt <palmer@sifive.com>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
James Morris James Morris <jmorris@namei.org>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
David Howells <dhowells@redhat.com>,
LSM List <linux-security-module@vger.kernel.org>,
keyrings@vger.kernel.org, linux-riscv@lists.infradead.org,
"Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: WARNING: refcount bug in find_key_to_update
Date: Thu, 17 Oct 2019 09:00:28 -0700 [thread overview]
Message-ID: <20191017160028.GA726@sol.localdomain> (raw)
In-Reply-To: <CAHk-=wjFozfjV34_qy3_Z155uz_Z7qFVfE8h=_9ceGU-SVk9hA@mail.gmail.com>
On Thu, Oct 17, 2019 at 08:53:06AM -0700, Linus Torvalds wrote:
> On Wed, Oct 16, 2019 at 7:42 PM syzbot
> <syzbot+6455648abc28dbdd1e7f@syzkaller.appspotmail.com> wrote:
> >
> > syzbot has bisected this bug to 0570bc8b7c9b ("Merge tag
> > 'riscv/for-v5.3-rc1' ...")
>
> Yeah, that looks unlikely. The only non-riscv changes are from
> documentation updates and moving a config variable around.
>
> Looks like the crash is quite unlikely, and only happens in one out of
> ten runs for the ones it has happened to.
>
> The backtrace looks simple enough, though:
>
> RIP: 0010:refcount_inc_checked+0x2b/0x30 lib/refcount.c:156
> __key_get include/linux/key.h:281 [inline]
> find_key_to_update+0x67/0x80 security/keys/keyring.c:1127
> key_create_or_update+0x4e5/0xb20 security/keys/key.c:905
> __do_sys_add_key security/keys/keyctl.c:132 [inline]
> __se_sys_add_key security/keys/keyctl.c:72 [inline]
> __x64_sys_add_key+0x219/0x3f0 security/keys/keyctl.c:72
> do_syscall_64+0xd0/0x540 arch/x86/entry/common.c:296
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> which to me implies that there's some locking bug, and somebody
> released the key without holding a lock.
>
> That code looks a bit confused to me. Releasing a key without holding
> a lock looks permitted, but if that's the case then __key_get() is
> complete garbage. It would need to use 'refcount_inc_not_zero()' and
> failure would require failing the caller.
>
> But I haven't followed the key locking rules, so who knows. That "put
> without lock" scenario would explain the crash, though.
>
> David?
>
Yes this is a bogus bisection.
The key is supposed to have refcount >= 1 since it's in a keyring.
So some bug is causing it to have refcount 0. Perhaps some place calling
key_put() too many times.
Unfortunately I can't get the reproducer to work locally.
Note that there are 2 other syzbot reports that look related.
No reproducers for them, though:
Title: KASAN: use-after-free Read in key_put
Last occurred: 1 day ago
Reported: 28 days ago
Branches: Mainline
Dashboard link: https://syzkaller.appspot.com/bug?id=f13750b1124e01191250cf930086dcc40740fa30
Original thread: https://lore.kernel.org/lkml/0000000000008c3e590592cf4b7f@google.com/T/#u
Title: KASAN: use-after-free Read in keyring_compare_object
Last occurred: 49 days ago
Reported: 84 days ago
Branches: Mainline
Dashboard link: https://syzkaller.appspot.com/bug?id=529ab6a98286c2a97c445988a62760a58d4a1d4b
Original thread: https://lore.kernel.org/lkml/000000000000038ef6058e6f3592@google.com/T/#u
- Eric
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next prev parent reply other threads:[~2019-10-17 16:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <000000000000830fe50595115344@google.com>
2019-10-17 2:42 ` WARNING: refcount bug in find_key_to_update syzbot
2019-10-17 15:53 ` Linus Torvalds
2019-10-17 16:00 ` Eric Biggers [this message]
2019-10-18 16:38 ` David Howells
2019-10-22 10:35 ` David Howells
2019-10-22 13:17 ` David Howells
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