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From: David Howells <dhowells@redhat.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: dhowells@redhat.com, Eric Biggers <ebiggers@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	syzbot <syzbot+6455648abc28dbdd1e7f@syzkaller.appspotmail.com>,
	keyrings@vger.kernel.org,
	LSM List <linux-security-module@vger.kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: WARNING: refcount bug in find_key_to_update
Date: Fri, 18 Oct 2019 17:45:41 +0100	[thread overview]
Message-ID: <31946.1571417141@warthog.procyon.org.uk> (raw)
In-Reply-To: <b211005b-75de-7936-c97a-817f7100415a@I-love.SAKURA.ne.jp>

Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:

> I don't know about keys, but I rather suspect lack of serialization locks
> between "looking up for checking existing keys" versus "looking up for
> garbage collection".

The garbage collector holds key_serial_lock when walking key_serial_tree
looking for keys to destroy.

As the gc is the *only* thing that is permitted to remove a key from
key_serial_tree, it can safely keep a cursor pointer to the node it was
looking at when it drops the lock - and then resume scanning once it has taken
the lock again.

When find_key_to_update() is looking for a key that might be updated, the
caller *must* be holding the destination keyring lock and every key in the
keyring should have at least one ref on it held by the keyring - so none of
them should get destroyed by the garbage collector.

David

  parent reply	other threads:[~2019-10-18 16:45 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-17  1:42 WARNING: refcount bug in find_key_to_update syzbot
2019-10-17  2:42 ` syzbot
2019-10-17 15:53   ` Linus Torvalds
2019-10-17 16:00     ` Eric Biggers
2019-10-18 10:54       ` Tetsuo Handa
2019-10-18 16:45       ` David Howells [this message]
2019-10-18 16:38   ` David Howells
2019-10-22 10:35   ` David Howells
2019-10-22 13:17   ` David Howells
2019-10-21 15:59 ` David Howells
2019-10-21 16:05   ` Dmitry Vyukov
     [not found] <20191017092428.7336-1-hdanton@sina.com>
2019-10-18 16:46 ` David Howells

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