Re: [Qemu-devel] [PATCH 4/4][RFC] Add logic to QEMU to read command line options from qcow2 images

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

On Wed, Aug 08, 2007 at 04:52:58PM -0300, Jorge Luc?ngeli Obes wrote:
> This patch makes QEMU check for command line options stored in qcow2 images.

I think it is a bad idea from a security POV to automatically extract & use 
command line args from  a disk image like this without the admin explicitly 
requesting this capability. 

eg If I grabbed a demo disk image from a vendors' or community website I would
certainly not trust whatever args may happen to be embedded in the disk image
and thus do not want QEMU to be automatically running using them.

I'd recommend having some command line flag to turn this capability on. For
example a '--args PATH-TO-DISK' flag,

  qemu --args $HOME/fedora.qcow

Would extract args from the disk image & us them.

While traditional

  qemu $HOME/fedora.qcow

would *not* extract args.

> diff --git a/qemu/vl.c b/qemu/vl.c
> index 4ad39f1..1d28794 100644
> --- a/qemu/vl.c
> +++ b/qemu/vl.c
> @@ -7000,6 +7012,58 @@ int main(int argc, char **argv)
>      nb_nics = 0;
>      /* default mac address of the first network interface */
> 
> +    bdrv_init();
> +
> +    drv = bdrv_find_format("qcow2");
> +
> +    if (argc > 1 && argv[1][0] != '-') {
> +        bs = bdrv_new("");
> +        if (!bs) {
> +            fprintf(stderr, "Not enough memory");
> +            exit(1);
> +        }
> +        if (bdrv_open2(bs, argv[1], 0, drv) < 0) {
> +            fprintf(stderr, "Could not open '%s'", argv[1]);
> +            bdrv_delete(bs);
> +            exit(1);
> +        }
> +
> +        tmpannot = bdrv_get_annot(bs, "commandline_args");
> +        if (tmpannot) {
> +            pstrcpy(annot, 1024, tmpannot);
> +
> +            do {
> +                tok = strtok(nbtoks == 0? tmpannot : NULL, " ");
> +
> +                if (tok != NULL)
> +                    nbtoks++;
> +                else
> +                    done = 1;
> +            } while (!done);
> +
> +            free(tmpannot);
> +
> +            if (nbtoks > 0) {
> +                char **argvprime = malloc((nbtoks + argc) * sizeof(char*));
> +
> +                for (i = 0; i < argc; i++)
> +                    argvprime[i] = argv[i];
> +
> +                for (i = 0; i < nbtoks; i++)
> +                    argvprime[i + argc] = strtok(i == 0? annot : NULL, " ");
> +
> +                argv = argvprime;
> +                argc = argc + nbtoks;
> +
> +                for (i = 0; i < nbtoks + 2; i++)
> +                    printf("argv[%d] = %s\n", i, argv[i]);
> +
> +            }
> +        }
> +
> +        bdrv_delete(bs);
> +    }
> +
>      optind = 1;
>      for(;;) {
>          if (optind >= argc)


Dan.
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