Re: [Qemu-devel] [PATCH 06/13] qcrypto-luks: implement more rigorous header checking

["Daniel P. Berrangé" <berrange@redhat.com>]

On Sun, Aug 25, 2019 at 07:08:00PM +0300, Maxim Levitsky wrote:
> On Sun, 2019-08-25 at 18:40 +0300, Maxim Levitsky wrote:
> > On Thu, 2019-08-22 at 12:04 +0100, Daniel P. Berrangé wrote:
> > > On Wed, Aug 14, 2019 at 11:22:12PM +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 doens't really matter.
> > > > 
> > > > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > > > ---
> > > >  crypto/block-luks.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> > > >  1 file changed, 42 insertions(+)
> > > > 
> > > > diff --git a/crypto/block-luks.c b/crypto/block-luks.c
> > > > index 336e633df4..1997e92fe1 100644
> > > > --- a/crypto/block-luks.c
> > > > +++ b/crypto/block-luks.c
> > > > @@ -551,6 +551,8 @@ static int
> > > >  qcrypto_block_luks_check_header(QCryptoBlockLUKS *luks, Error **errp)
> > > >  {
> > > >      int ret;
> > > > +    int i, j;
> > > > +
> > > >  
> > > >      if (memcmp(luks->header.magic, qcrypto_block_luks_magic,
> > > >                 QCRYPTO_BLOCK_LUKS_MAGIC_LEN) != 0) {
> > > > @@ -566,6 +568,46 @@ qcrypto_block_luks_check_header(QCryptoBlockLUKS *luks, Error **errp)
> > > >          goto fail;
> > > >      }
> > > >  
> > > > +    /* Check all keyslots for corruption  */
> > > > +    for (i = 0 ; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS ; i++) {
> > > > +
> > > > +        QCryptoBlockLUKSKeySlot *slot1 = &luks->header.key_slots[i];
> > > > +        uint start1 = slot1->key_offset;
> > > > +        uint len1 = splitkeylen_sectors(luks, slot1->stripes);
> > > 
> > > Using 'uint' is not normal QEMU style.
> > > 
> > > Either use 'unsigned int'  or if a specific size is needed
> > > then one of the 'guintNN' types from glib.
> > > 
> > > This applies elsewhere in this patch series too, but
> > > I'll only comment here & let you find the other cases.
> > 
> > Fixed. Sorry for the noise.
> > 
> > > 
> > > > +
> > > > +        if (slot1->stripes == 0 ||
> > > > +                (slot1->active != QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED &&
> > > > +                slot1->active != QCRYPTO_BLOCK_LUKS_KEY_SLOT_ENABLED)) {
> > > > +
> > > 
> > > Redundant blank line
> > 
> > Fixed
> > > 
> > > > +            error_setg(errp, "Keyslot %i is corrupted", i);
> > > 
> > > I'd do a separate check for stripes and active fields, and then give a
> > > specific error message for each. That way if this does ever trigger
> > > in practice will immediately understand which check failed.
> > > 
> > > Also using '%d' rather than '%i' is more common convention
> > 
> > Done.
> 
> Note that I switched i,j to be size_t since you said that you prefer this,
> and to print this I apparently need %lu.

For size_t, you need %zu to be 32/64-bit agnostic  (ssize_t is %zd)


Regards,
Daniel
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