linux-kernel - Re: [RFC PATCH v2] keys: update key quotas in key

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Date: Mon, 29 Jan 2024 11:23:59 +0000
From: Luis Henriques <lhenriques@...e.de>
To: Eric Biggers <ebiggers@...nel.org>
Cc: David Howells <dhowells@...hat.com>,  Jarkko Sakkinen
 <jarkko@...nel.org>,  keyrings@...r.kernel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] keys: update key quotas in key_put()

Eric Biggers <ebiggers@...nel.org> writes:

> On Fri, Jan 26, 2024 at 04:12:59PM +0000, Luis Henriques wrote:
>> Eric Biggers <ebiggers@...nel.org> writes:
>> 
>> > On Mon, Jan 15, 2024 at 12:03:00PM +0000, Luis Henriques wrote:
>> >> Delaying key quotas update when key's refcount reaches 0 in key_put() has
>> >> been causing some issues in fscrypt testing.  This patches fixes this test
>> >> flakiness by dealing with the quotas immediately, but leaving all the other
>> >> clean-ups to the key garbage collector.  Unfortunately, this means that we
>> >> also need to switch to the irq-version of the spinlock that protects quota.
>> >> 
>> >> Signed-off-by: Luis Henriques <lhenriques@...e.de>
>> >> ---
>> >> Hi David!
>> >> 
>> >> I have these changes in my local disk for a while; I wanted to send them
>> >> before EOY break but... yeah, it didn't happen.  Anyway, I'm still sending
>> >> it as an RFC as I'm probably missing something.
>> >> 
>> >>  security/keys/gc.c     |  8 --------
>> >>  security/keys/key.c    | 32 ++++++++++++++++++++++----------
>> >>  security/keys/keyctl.c | 11 ++++++-----
>> >>  3 files changed, 28 insertions(+), 23 deletions(-)
>> >
>> > This patch seems reasonable to me, though I'm still thinking about changing
>> > fs/crypto/ to manage its key quotas itself which would avoid the issue entirely.
>> >
>> > Note that as I said before, fs/crypto/ does key_put() on a whole keyring at
>> > once, in order to release the quota of the keys in the keyring.  Do you plan to
>> > also change fs/crypto/ to keyring_clear() the keyring before putting it?
>> > Without that, I don't think the problem is solved, as the quota release will
>> > still happen asynchronously due to the keyring being cleared asynchronously.
>> 
>> Ah, good point.  In the meantime I had forgotten everything about this
>> code and missed that.  So, I can send another patch to fs/crypto to add
>> that extra call once (or if) this patch is accepted.
>> 
>> If I'm reading the code correctly, the only place where this extra call is
>> required is on fscrypt_put_master_key():
>> 
>> diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
>> index 0edf0b58daa7..4afd32f1aed9 100644
>> --- a/fs/crypto/keyring.c
>> +++ b/fs/crypto/keyring.c
>> @@ -74,6 +74,7 @@ void fscrypt_put_master_key(struct fscrypt_master_key *mk)
>>  	 * that concurrent keyring lookups can no longer find it.
>>  	 */
>>  	WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0);
>> +	keyring_clear(mk->mk_users);
>>  	key_put(mk->mk_users);
>>  	mk->mk_users = NULL;
>
> This will need a NULL check, since keyring_clear() doesn't accept NULL:
>
> 	if (mk->mk_users) {
> 		keyring_clear(mk->mk_users);
> 		key_put(mk->mk_users);
> 		mk->mk_users = NULL;
> 	}
>

Ah, good point.  Makes sense.

>>  	call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
>> 
>> On the other hand, if you're really working towards dropping this code
>> entirely, maybe there's not point doing that.
>
> Well, it depends whether this patch (the one for security/keys/) is accepted or
> not.  If it's accepted, I think it makes sense to add the keyring_clear() and
> otherwise keep the fs/crypto/ code as-is.  If it's not accepted, I think I'll
> have to make fs/crypto/ handle the quotas itself.

Awesome, thank.

David, do you have any feedback on this patch or would you rather have me
send v3, addressing Jarkko comments regarding the commit message?

Cheers,
-- 
Luís