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Re: [PATCH v9 5/7] cryptodisk: Add options to cryptomount to support key


From: Glenn Washburn
Subject: Re: [PATCH v9 5/7] cryptodisk: Add options to cryptomount to support keyfiles
Date: Thu, 5 May 2022 18:03:12 -0500

On Fri, 29 Apr 2022 15:03:01 +0200
Daniel Kiper <dkiper@net-space.pl> wrote:

> On Mon, Apr 11, 2022 at 06:40:26AM +0000, Glenn Washburn wrote:
> > From: John Lane <john@lane.uk.net>
> >
> > Add the options --key-file, --keyfile-offset, and --keyfile-size to
> > cryptomount and code to put read the requested key file data and pass
> > via the cargs struct. Note, key file data is for all intents and purposes
> > equivalent to a password given to cryptomount. So there is no need to
> > enable support for key files in the various crypto backends (eg. LUKS1)
> > because the key data is passed just as if it were a password.
> >
> > Signed-off-by: John Lane <john@lane.uk.net>
> > GNUtoo@cyberdimension.org: rebase, patch split, small fixes, commit message
> > Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
> > development@efficientek.com: rebase and rework to use cryptomount arg 
> > passing,
> >   minor fixes, improve commit message
> > Signed-off-by: Glenn Washburn <development@efficientek.com>
> > ---
> >  grub-core/disk/cryptodisk.c | 85 ++++++++++++++++++++++++++++++++++++-
> >  include/grub/cryptodisk.h   |  2 +
> >  include/grub/file.h         |  2 +
> >  3 files changed, 88 insertions(+), 1 deletion(-)
> >
> > diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
> > index 063997d2f0..155cc7f0b4 100644
> > --- a/grub-core/disk/cryptodisk.c
> > +++ b/grub-core/disk/cryptodisk.c
> > @@ -43,6 +43,9 @@ static const struct grub_arg_option options[] =
> >      {"boot", 'b', 0, N_("Mount all volumes with `boot' flag set."), 0, 0},
> >      {"password", 'p', 0, N_("Password to open volumes."), 0, 
> > ARG_TYPE_STRING},
> >      {"header", 'H', 0, N_("Read header from file"), 0, ARG_TYPE_STRING},
> > +    {"key-file", 'k', 0, N_("Key file"), 0, ARG_TYPE_STRING},
> > +    {"keyfile-offset", 'O', 0, N_("Key file offset (bytes)"), 0, 
> > ARG_TYPE_INT},
> > +    {"keyfile-size", 'S', 0, N_("Key file data size (bytes)"), 0, 
> > ARG_TYPE_INT},
> >      {0, 0, 0, 0, 0, 0}
> >    };
> >
> > @@ -1185,6 +1188,84 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, 
> > int argc, char **args)
> >     return grub_errno;
> >      }
> >
> > +  if (state[5].set) /* keyfile */
> > +    {
> > +      const char *p = NULL;
> > +      grub_file_t keyfile;
> > +      int keyfile_offset;
> 
> I think this should be unsigned long if you do grub_strtoul() below.
> 
> > +      grub_size_t keyfile_size = 0;
> 
> I think this should be unsigned long too.

Ok.

> > +
> > +
> 
> Please drop this extra line.
> 
> > +      if (state[6].set) /* keyfile-offset */
> > +   {
> > +     keyfile_offset = grub_strtoul (state[6].arg, &p, 0);
> 
> Are you sure you want 0 base?

Having base 0 tells grub_strtoull that it should guess the base, which
means base 16 if a "0x" prefix, base 8 if "0" prefix, and base 10
otherwise. This is conventient for the user.

> > +     if (grub_errno != GRUB_ERR_NONE)
> > +       return grub_errno;
> > +
> > +     if (*p != '\0')
> > +       return grub_error (GRUB_ERR_BAD_ARGUMENT,
> > +                          N_("unrecognized number"));
> 
> This error check is unreliable. Please take a look at the commit
> ac8a37dda (net/http: Allow use of non-standard TCP/IP ports) how it
> should be done.

Ok.

> > +   }
> > +      else
> > +   {
> > +     keyfile_offset = 0;
> > +   }
> 
> Why do not initialize it in definition above? If not please drop {}.

I guess it was to avoid an unnecessary write if the if is true. But
yeah, I don't think it gets you much.

> > +      if (state[7].set) /* keyfile-size */
> > +   {
> > +     keyfile_size = grub_strtoul (state[7].arg, &p, 0);
> > +
> > +     if (*p != '\0')
> > +       return grub_error (GRUB_ERR_BAD_ARGUMENT,
> > +                          N_("unrecognized number"));
> > +
> > +     if (grub_errno != GRUB_ERR_NONE)
> > +       return grub_errno;
> 
> Again, these checks are not reliable...

Are you also saying grub_errno shouldn't be checked here? That doesn't
seem correct to me.

> > +     if (keyfile_size > GRUB_CRYPTODISK_MAX_KEYFILE_SIZE)

This is where the macro at the end of the patch is used.

> > +       return grub_error (GRUB_ERR_OUT_OF_RANGE,
> > +                          N_("key file size exceeds maximum (%d)"),
> > +                          GRUB_CRYPTODISK_MAX_KEYFILE_SIZE);
> > +
> > +     if (keyfile_size == 0)
> > +       return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("key file size is 0"));
> > +   }
> > +
> > +      keyfile = grub_file_open (state[5].arg,
> > +                           GRUB_FILE_TYPE_CRYPTODISK_ENCRYPTION_KEY);
> > +      if (keyfile == NULL)
> 
> Yeah, I like compare with NULL... :-)
> 
> > +   return grub_errno;
> > +
> > +      if (grub_file_seek (keyfile, keyfile_offset) == (grub_off_t)-1)
> 
> Space before -1 please...

Ok.

> > +   return grub_errno;
> > +
> > +      if (keyfile_size > 0)
> > +   {
> > +     if (keyfile_size > (keyfile->size - keyfile_offset))
> 
> What if somebody passes keyfile_offset larger than keyfile->size?
> I would use grub_sub() here and check for underflow.

Good point, I'll clamp it down to keyfile->size above.

> > +       return grub_error (GRUB_ERR_FILE_READ_ERROR,
> > +                          N_("keyfile is too small: "
> > +                             "requested %" PRIuGRUB_SIZE " bytes, "
> > +                             "but the file only has %" PRIuGRUB_UINT64_T
> > +                             " bytes"),
> > +                          keyfile_size,
> > +                          keyfile->size);
> > +
> > +     cargs.key_len = keyfile_size;
> > +   }
> > +      else
> > +   {
> > +     cargs.key_len = keyfile->size - keyfile_offset;
> 
> grub_sub() again?

With keyfile_offset <= keyfile->size, this shouldn't be a problem.

> > +   }
> 
> Please drop {} here...

Yep.

> > +      cargs.key_data = grub_malloc (cargs.key_len);
> > +      if (cargs.key_data == NULL)
> > +   return GRUB_ERR_OUT_OF_MEMORY;
> > +
> > +      if (grub_file_read (keyfile, cargs.key_data, cargs.key_len) != 
> > (grub_ssize_t) cargs.key_len)
> > +   return grub_error (GRUB_ERR_FILE_READ_ERROR, (N_("reading key file")));
> > +    }
> > +
> >    if (state[0].set) /* uuid */
> >      {
> >        int found_uuid;
> > @@ -1397,7 +1478,9 @@ GRUB_MOD_INIT (cryptodisk)
> >  {
> >    grub_disk_dev_register (&grub_cryptodisk_dev);
> >    cmd = grub_register_extcmd ("cryptomount", grub_cmd_cryptomount, 0,
> > -                         N_("[-p password] [-H file] <SOURCE|-u 
> > UUID|-a|-b>"),
> > +                         N_("[ [-p password] | [-k keyfile"
> > +                            " [-O keyoffset] [-S keysize] ] ] [-H file]"
> > +                            " <SOURCE|-u UUID|-a|-b>"),
> >                           N_("Mount a crypto device."), options);
> >    grub_procfs_register ("luks_script", &luks_script);
> >  }
> > diff --git a/include/grub/cryptodisk.h b/include/grub/cryptodisk.h
> > index 9fe451de92..d94df68b65 100644
> > --- a/include/grub/cryptodisk.h
> > +++ b/include/grub/cryptodisk.h
> > @@ -62,6 +62,8 @@ typedef enum
> >  #define GRUB_CRYPTODISK_MAX_KEYLEN 128
> >  #define GRUB_CRYPTODISK_MAX_PASSPHRASE 256
> >
> > +#define GRUB_CRYPTODISK_MAX_KEYFILE_SIZE 8192
> 
> This constant is not used here. I think it should be used in this patch
> to check limits. Probably somewhere around proposed grub_sub(). Than
> maybe we do not need grub_sub().

Yep, its used, see above.

Glenn



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