Re: [Qemu-devel] [PATCH] hw/9pfs: Handle Security model parsing

["M. Mohan Kumar" <mohan@in.ibm.com>]

-- 
Regards,
M. Mohan Kumar
On Wednesday, October 12, 2011 01:58:00 PM Daniel P. Berrange wrote:
> On Wed, Oct 12, 2011 at 01:24:16PM +0530, M. Mohan Kumar wrote:
> > Security model is needed only for 'local' fs driver.
> > 
> > Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
> > ---
> > 
> >  fsdev/qemu-fsdev.c         |    6 +----
> >  fsdev/qemu-fsdev.h         |    1 +
> >  hw/9pfs/virtio-9p-device.c |   47
> >  ++++++++++++++++++++++--------------------- vl.c                      
> >  |   20 +++++++++++++++--
> >  4 files changed, 43 insertions(+), 31 deletions(-)
> > 
> > --- a/fsdev/qemu-fsdev.h
> > +++ b/fsdev/qemu-fsdev.h
> > @@ -40,6 +40,7 @@ typedef struct FsTypeTable {
> > 
> >  typedef struct FsTypeEntry {
> >  
> >      char *fsdev_id;
> >      char *path;
> > 
> > +    char *fsdriver;
> > 
> >      char *security_model;
> >      int cache_flags;
> >      FileOperations *ops;
> > 
> > diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> > index aac58ad..1846e36 100644
> > --- a/hw/9pfs/virtio-9p-device.c
> > +++ b/hw/9pfs/virtio-9p-device.c
> > @@ -83,29 +83,30 @@ VirtIODevice *virtio_9p_init(DeviceState *dev,
> > V9fsConf *conf)
> > 
> >          exit(1);
> >      
> >      }
> > 
> > -    if (!strcmp(fse->security_model, "passthrough")) {
> > -        /* Files on the Fileserver set to client user credentials */
> > -        s->ctx.fs_sm = SM_PASSTHROUGH;
> > -        s->ctx.xops = passthrough_xattr_ops;
> > -    } else if (!strcmp(fse->security_model, "mapped")) {
> > -        /* Files on the fileserver are set to QEMU credentials.
> > -         * Client user credentials are saved in extended attributes.
> > -         */
> > -        s->ctx.fs_sm = SM_MAPPED;
> > -        s->ctx.xops = mapped_xattr_ops;
> > -    } else if (!strcmp(fse->security_model, "none")) {
> > -        /*
> > -         * Files on the fileserver are set to QEMU credentials.
> > -         */
> > -        s->ctx.fs_sm = SM_NONE;
> > -        s->ctx.xops = none_xattr_ops;
> > -    } else {
> > -        fprintf(stderr, "Default to security_model=none. You may want"
> > -                " enable advanced security model using "
> > -                "security option:\n\t security_model=passthrough\n\t "
> > -                "security_model=mapped\n");
> > -        s->ctx.fs_sm = SM_NONE;
> > -        s->ctx.xops = none_xattr_ops;
> > +    /* security models is needed only for local fs driver */
> > +    if (!strcmp(fse->fsdriver, "local")) {
> > +        if (!strcmp(fse->security_model, "passthrough")) {
> > +            /* Files on the Fileserver set to client user credentials */
> > +            s->ctx.fs_sm = SM_PASSTHROUGH;
> > +            s->ctx.xops = passthrough_xattr_ops;
> > +        } else if (!strcmp(fse->security_model, "mapped")) {
> > +            /* Files on the fileserver are set to QEMU credentials.
> > +            * Client user credentials are saved in extended attributes.
> > +            */
> > +            s->ctx.fs_sm = SM_MAPPED;
> > +            s->ctx.xops = mapped_xattr_ops;
> > +        } else if (!strcmp(fse->security_model, "none")) {
> > +            /*
> > +            * Files on the fileserver are set to QEMU credentials.
> > +            */
> > +            s->ctx.fs_sm = SM_NONE;
> > +            s->ctx.xops = none_xattr_ops;
> > +        } else {
> > +            fprintf(stderr, "Invalid security_model %s specified.\n"
> > +                    "Available security models are:\t "
> > +                    "passthrough,mapped or none\n",
> > fse->security_model); +            exit(1);
> > +        }
> 
> Are you sure there aren't use cases where people would like to
> choose between  passthrough & mapped, even when using the 'proxy'
> or 'handle' security drivers.
>
Proxy FS driver is added to overcome the limit imposed by local + passthrough 
security model combination that needs qemu to be started by root user. Mapped 
and none secuiry model can be used by non root user also.

So Proxy FS driver does not need any security model(its pass-through only)
 
> Both of the security models seem pretty generally useful to me,
> regardless of the driver type.
>