[Libguestfs] [PATCH 2/2] builder: use a disposable GPG keyring for every Sigchecker

[Richard W.M. Jones]

On Thu, Feb 20, 2014 at 11:53:17AM +0100, Pino Toscano wrote:
> Create a temporary directory and tell gpg to use it as homedir, so
> imported keys do not get into the user's keyring. This also avoid
> importing the default key when a different one is needed to check the
> signature.
> 
> The only exception is when a non-default fingerprint is used: in this
> case, that key is read from the user's keyring, since it is where it is.

The mkdtemp part is fine.  You could spin that off into a separate
commit, so it could be a candidate for backporting.

The rest I found a bit confusing.  What does it do exactly?

> diff --git a/builder/sigchecker.ml b/builder/sigchecker.ml
> index b20a186..10e342e 100644
> --- a/builder/sigchecker.ml
> +++ b/builder/sigchecker.ml
> @@ -95,21 +95,38 @@ ZvXkQ3FVJwZoLmHw47vvlVpLD/4gi1SuHWieRvZ+UdDq00E348pm
>  =neBW
>  -----END PGP PUBLIC KEY BLOCK-----
>  "
> -let key_imported = ref false
>  
>  type t = {
>    debug : bool;
>    gpg : string;
>    fingerprint : string;
>    check_signature : bool;
> +  gpghome : string;
> +  mutable key_imported : bool;
>  }
>  
>  let create ~debug ~gpg ~fingerprint ~check_signature =
> +  (* Create a temporary directory for gnupg. *)
> +  let tmpdir = Mkdtemp.mkdtemp (Filename.temp_dir_name // "vb.gpghome.XXXXXX") in
> +  rmdir_on_exit tmpdir;
> +  (* Run gpg once, so it can setup its own home directory, failing
> +   * if it cannot.
> +   *)
> +  let cmd = sprintf "%s --homedir %s --list-keys%s"
> +    gpg tmpdir (if debug then "" else " >/dev/null 2>&1") in
> +  if debug then eprintf "%s\n%!" cmd;
> +  let r = Sys.command cmd in
> +  if r <> 0 then (
> +    eprintf (f_"virt-builder: error: GPG failure: could not run GPG the first time\nUse the '-v' option and look for earlier error messages.\n");
> +    exit 1
> +  );
>    {
>      debug = debug;
>      gpg = gpg;
>      fingerprint = fingerprint;
>      check_signature = check_signature;
> +    gpghome = tmpdir;
> +    key_imported = false;
>    }
>  
>  (* Compare two strings of hex digits ignoring whitespace and case. *)
> @@ -159,8 +176,9 @@ and do_verify t args =
>    let status_file = Filename.temp_file "vbstat" ".txt" in
>    unlink_on_exit status_file;
>    let cmd =
> -    sprintf "%s --verify%s --status-file %s %s"
> -        t.gpg (if t.debug then "" else " -q --logger-file /dev/null")
> +    sprintf "%s --homedir %s --verify%s --status-file %s %s"
> +        t.gpg t.gpghome
> +        (if t.debug then "" else " -q --logger-file /dev/null")
>          (quote status_file) args in
>    if t.debug then eprintf "%s\n%!" cmd;
>    let r = Sys.command cmd in
> @@ -188,23 +206,40 @@ and do_verify t args =
>      exit 1
>    )
>  
> -(* Import the default public key. *)
> +(* Import the requested public key. *)
>  and import_key t =
> -  if not !key_imported then (
> -    let filename, chan = Filename.open_temp_file "vbpubkey" ".asc" in
> -    unlink_on_exit filename;
> -    output_string chan default_pubkey;
> -    close_out chan;
> -
> -    let cmd = sprintf "%s --import %s%s"
> -      t.gpg (quote filename)
> +  if not t.key_imported then (
> +    let keyfile = ref "" in
> +    if equal_fingerprints default_fingerprint t.fingerprint then (
> +      let filename, chan = Filename.open_temp_file "vbpubkey" ".asc" in
> +      unlink_on_exit filename;
> +      output_string chan default_pubkey;
> +      close_out chan;
> +      keyfile := filename
> +    ) else (
> +      let filename = Filename.temp_file "vbpubkey" ".asc" in
> +      unlink_on_exit filename;
> +      let cmd = sprintf "%s --yes --armor --output %s --export %s%s"
> +        t.gpg (quote filename) (quote t.fingerprint)
> +        (if t.debug then "" else " >/dev/null 2>&1") in
> +      if t.debug then eprintf "%s\n%!" cmd;
> +      let r = Sys.command cmd in
> +      if r <> 0 then (
> +        eprintf (f_"virt-builder: error: could not export public key\nUse the '-v' option and look for earlier error messages.\n");
> +        exit 1
> +      );
> +      keyfile := filename
> +    );
> +
> +    let cmd = sprintf "%s --homedir %s --import %s%s"
> +      t.gpg t.gpghome (quote !keyfile)
>        (if t.debug then "" else " >/dev/null 2>&1") in
>      let r = Sys.command cmd in
>      if r <> 0 then (
>        eprintf (f_"virt-builder: error: could not import public key\nUse the '-v' option and look for earlier error messages.\n");
>        exit 1
>      );
> -    key_imported := true
> +    t.key_imported <- true
>    )
>  
>  type csum_t = SHA512 of string

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/