linux-kernel - Re: inconsistent lock state in ima_process_queued

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Message-ID: <52f0bced-2d8b-bdf4-b65a-26689ea1aed1@linux.microsoft.com>
Date:   Tue, 14 Jan 2020 09:19:06 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Cc:     syzbot <syzbot+a4a503d7f37292ae1664@...kaller.appspotmail.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <jmorris@...ei.org>,
        linux-integrity@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: inconsistent lock state in ima_process_queued_keys

Hi Dmitry,

> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -103,17 +103,18 @@ static bool ima_queue_key(struct key *keyring,
> const void *payload,
>   {
>          bool queued = false;
>          struct ima_key_entry *entry;
> +       unsigned long flags;
> 
>          entry = ima_alloc_key_entry(keyring, payload, payload_len);
>          if (!entry)
>                  return false;
> 
> -       spin_lock(&ima_keys_lock);
> +       spin_lock_irqsave(&ima_keys_lock, flags);
>          if (!ima_process_keys) {
>                  list_add_tail(&entry->list, &ima_keys);
>                  queued = true;
>          }
> -       spin_unlock(&ima_keys_lock);
> +       spin_unlock_irqrestore(&ima_keys_lock, flags);
> 
>          if (!queued)
>                  ima_free_key_entry(entry);
> 

Using sping_lock_irqsave() and spin_lock_irqrestore() in ima_queue_key() 
is the right approach. Found a relevant blog below:

https://stackoverflow.com/questions/50637489/spin-lock-irqsave-in-interrupt-context

I think it would be safe to use the same spinlock functions in 
ima_process_queued_keys() as well, but not a must.

Could you please confirm if your change fixed the crash?
I'll post a patch shortly.

thanks,
  -lakshmi