Re: [Qemu-devel] [PATCH v2 13/13] qcrypto-luks: implement more rigorous header checking

[Maxim Levitsky]

On Fri, 2019-09-06 at 14:34 +0100, Daniel P. Berrangé wrote:
> On Mon, Aug 26, 2019 at 04:51:03PM +0300, Maxim Levitsky wrote:
> > Check that keyslots don't overlap with the data,
> > and check that keyslots don't overlap with each other.
> > (this is done using naive O(n^2) nested loops,
> > but since there are just 8 keyslots, this doesn't really matter.
> > 
> > Signed-off-by: Maxim Levitsky <address@hidden>
> > ---
> >  crypto/block-luks.c | 46 +++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 44 insertions(+), 2 deletions(-)
> > 
> > diff --git a/crypto/block-luks.c b/crypto/block-luks.c
> > index db0fb764b4..fdf4c41f8a 100644
> > --- a/crypto/block-luks.c
> > +++ b/crypto/block-luks.c
> > @@ -541,12 +541,12 @@ fail:
> >  static int
> >  qcrypto_block_luks_check_header(const QCryptoBlockLUKS *luks, Error **errp)
> >  {
> > -    int ret;
> > +    int ret = -EINVAL;
> 
> As before, no need to use errnos, just return -1 immediately.
> 
> > +    size_t i, j;
> >  
> >      if (memcmp(luks->header.magic, qcrypto_block_luks_magic,
> >                 QCRYPTO_BLOCK_LUKS_MAGIC_LEN) != 0) {
> >          error_setg(errp, "Volume is not in LUKS format");
> > -        ret = -EINVAL;
> >          goto fail;
> >      }
> >  
> > @@ -557,6 +557,48 @@ qcrypto_block_luks_check_header(const QCryptoBlockLUKS 
> > *luks, Error **errp)
> >          goto fail;
> >      }
> >  
> > +    /* Check all keyslots for corruption  */
> > +    for (i = 0 ; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS ; i++) {
> > +
> > +        const QCryptoBlockLUKSKeySlot *slot1 = &luks->header.key_slots[i];
> > +        unsigned int start1 = slot1->key_offset_sector;
> > +        unsigned int len1 =
> > +            qcrypto_block_luks_splitkeylen_sectors(luks, slot1->stripes);
> > +
> > +        if (slot1->stripes == 0) {
> > +            error_setg(errp, "Keyslot %zu is corrupted (stripes == 0)", i);
> > +            goto fail;
> > +        }
> 
> How about checking stripes != QCRYPTO_BLOCK_LUKS_STRIPES because
> AFAIR, you're required to use 4k stripes in luks v1.
I see that spec does allow for user defined number of stripes.

> 
> Also how about  checking    iters >= MIN_SLOT_KEY_ITERS
Also this is only a suggested minimum

> 
> > +
> > +        if (slot1->active != QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED &&
> > +                slot1->active != QCRYPTO_BLOCK_LUKS_KEY_SLOT_ENABLED) {
> 
> Align the two lines with (
Done
> 
> > +            error_setg(errp,
> > +                       "Keyslot %zu state (active/disable) is corrupted", 
> > i);
> > +            goto fail;
> > +        }
> > +
> > +        if (start1 + len1 > luks->header.payload_offset_sector) {
> > +            error_setg(errp,
> > +                       "Keyslot %zu is overlapping with the encrypted 
> > payload",
> > +                       i);
> > +            goto fail;
> > +        }
> > +
> > +        for (j = i + 1 ; j < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS ; j++) {
> > +            const QCryptoBlockLUKSKeySlot *slot2 = 
> > &luks->header.key_slots[j];
> > +            unsigned int start2 = slot2->key_offset_sector;
> > +            unsigned int len2 =
> > +                qcrypto_block_luks_splitkeylen_sectors(luks, 
> > slot2->stripes);
> > +
> > +            if (start1 + len1 > start2 && start2 + len2 > start1) {
> > +                error_setg(errp,
> > +                           "Keyslots %zu and %zu are overlapping in the 
> > header",
> > +                           i, j);
> > +                goto fail;
> > +            }
> > +        }
> > +
> > +    }
> >      return 0;
> >  fail:
> >      return ret;
> > -- 
> > 2.17.2
> > 
> 
> Regards,
> Daniel

Best regards,
        Maxim Levitsky