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From: Max Reitz <mreitz@redhat.com>
Message-ID: <b6811e30-abd5-5f91-7b2b-7f10bd7feba5@redhat.com>
Date: Tue, 14 Nov 2017 16:27:56 +0100
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Subject: Re: [Qemu-devel] [PATCH for-2.11 4/5] qcow2: Add bounds check to
 get_refblock_offset()
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To: Alberto Garcia <berto@igalia.com>, qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org, Kevin Wolf <kwolf@redhat.com>, John Snow <jsnow@redhat.com>

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From: Max Reitz <mreitz@redhat.com>
To: Alberto Garcia <berto@igalia.com>, qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org, Kevin Wolf <kwolf@redhat.com>,
 John Snow <jsnow@redhat.com>
Message-ID: <b6811e30-abd5-5f91-7b2b-7f10bd7feba5@redhat.com>
Subject: Re: [PATCH for-2.11 4/5] qcow2: Add bounds check to
 get_refblock_offset()
References: <20171110203111.7666-1-mreitz@redhat.com>
 <20171110203111.7666-5-mreitz@redhat.com>
 <w511sl0299i.fsf@maestria.local.igalia.com>
In-Reply-To: <w511sl0299i.fsf@maestria.local.igalia.com>
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On 2017-11-14 16:02, Alberto Garcia wrote:
> On Fri 10 Nov 2017 09:31:10 PM CET, Max Reitz wrote:
>> +static int64_t get_refblock_offset(BlockDriverState *bs, uint64_t off=
set)
>> +{
>> +    BDRVQcow2State *s =3D bs->opaque;
>> +    uint32_t index =3D offset_to_reftable_index(s, offset);
>> +    int64_t covering_refblock_offset =3D 0;
>> +
>> +    if (index < s->refcount_table_size) {
>> +        covering_refblock_offset =3D s->refcount_table[index] & REFT_=
OFFSET_MASK;
>> +    }
>> +    if (!covering_refblock_offset) {
>> +        qcow2_signal_corruption(bs, true, -1, -1, "Refblock at %#" PR=
Ix64 " is "
>> +                                "not covered by the refcount structur=
es",
>> +                                offset);
>> +        return -EIO;
>> +    }
>> +
>> +    return covering_refblock_offset;
>> +}
>=20
> Isn't it simpler to do something like this instead?
>=20
>    if (index >=3D s->refcount_table_size) {
>        qcow2_signal_corruption(...);
>        return -EIO;
>    }
>    return s->refcount_table[index] & REFT_OFFSET_MASK;

But that doesn't cover the case were s->refcount_table[index] &
REFT_OFFSET_MASK is 0.

Max


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