linux-kernel - Re: [syzbot] [crypto?] KCSAN: data-race in random_recv_done / virtio

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Message-ID: <ZFI102tIiZFiZNK4@gondor.apana.org.au>
Date:   Wed, 3 May 2023 18:22:11 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+726dc8c62c3536431ceb@...kaller.appspotmail.com>,
        davem@...emloft.net, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, olivia@...enic.com,
        syzkaller-bugs@...glegroups.com, Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Laurent Vivier <lvivier@...hat.com>
Subject: Re: [syzbot] [crypto?] KCSAN: data-race in random_recv_done /
 virtio_read (3)

On Fri, Apr 21, 2023 at 04:52:13PM +0200, Dmitry Vyukov wrote:
>
> Here this:
> 
> size = min_t(unsigned int, size, vi->data_avail);
> memcpy(buf, vi->data + vi->data_idx, size);
> vi->data_idx += size;
> vi->data_avail -= size;
> 
> runs concurrently with:
> 
> if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
>     return;
> vi->data_idx = 0;
> 
> I did not fully grasp how/where vi->data is populated, but it looks
> like it can lead to use of uninit/stale random data, or even to out of
> bounds access, say if vi->data_avail is already updated, but
> vi->data_idx is not yet reset to 0. Then concurrent reading will read
> not where it's supposed to read.

This appears to be a genuine bug.  I'll look into it.

Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt