Re: [PATCH 6/6] misc: fastrpc: Restrict untrusted app to attach to privileged PD

[Joel Selvaraj]

Hi greg k-h,

The git commit id is: bab2f5e8fd5d2f759db26b78d9db57412888f187

But I am bit hesitant if we should revert it because there is a CVE 
attached to it: https://ubuntu.com/security/CVE-2024-41024

Also, I am ok with changing userspace if it's necessary. It would be 
nice if the authors can clarify the ideal fix here.

Regards,
Joel Selvaraj

On 8/15/24 00:15, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> On Thu, Aug 15, 2024 at 02:34:18AM +0000, Selvaraj, Joel (MU-Student) wrote:
> > Hi Srinivas Kandagatla and Ekansh Gupta,
> >
> > On 6/28/24 06:45, srinivas.kandagatla@xxxxxxxxxx wrote:
> > > From: Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx>
> > >
> > > Untrusted application with access to only non-secure fastrpc device
> > > node can attach to root_pd or static PDs if it can make the respective
> > > init request. This can cause problems as the untrusted application
> > > can send bad requests to root_pd or static PDs. Add changes to reject
> > > attach to privileged PDs if the request is being made using non-secure
> > > fastrpc device node.
> > >
> > > Fixes: 0871561055e6 ("misc: fastrpc: Add support for audiopd")
> > > Cc: stable <stable@xxxxxxxxxx>
> > > Signed-off-by: Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx>
> > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > > ---
> > >    drivers/misc/fastrpc.c      | 22 +++++++++++++++++++---
> > >    include/uapi/misc/fastrpc.h |  3 +++
> > >    2 files changed, 22 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > > index 5680856c0fb8..a7a2bcedb37e 100644
> > > --- a/drivers/misc/fastrpc.c
> > > +++ b/drivers/misc/fastrpc.c
> > > @@ -2087,6 +2087,16 @@ static int fastrpc_req_mem_map(struct fastrpc_user *fl, char __user *argp)
> > >      return err;
> > >    }
> > >
> > > +static int is_attach_rejected(struct fastrpc_user *fl)
> > > +{
> > > +   /* Check if the device node is non-secure */
> > > +   if (!fl->is_secure_dev) {
> > > +           dev_dbg(&fl->cctx->rpdev->dev, "untrusted app trying to attach to privileged DSP PD\n");
> > > +           return -EACCES;
> > > +   }
> > > +   return 0;
> > > +}
> >
> > This broke userspace for us. Sensors stopped working in SDM845 and other
> > qcom SoC devices running postmarketOS. Trying to communicate with the
> > fastrpc device just ends up with a permission denied error. This was
> > previously working. I am not sure if this is intended. Here are my two
> > observations:
> >
> > 1. if change the if condition to
> >
> > `if (!fl->is_secure_dev && fl->cctx->secure)`
> >
> > similar to how it's done in fastrpc's `is_session_rejected()` function,
> > then it works. But I am not sure if this is an valid fix. But currently,
> > fastrpc will simply deny access to all fastrpc device that contains the
> > `qcom,non-secure-domain` dt property. Is that the intended change?
> > Because I see a lot of adsp, cdsp and sdsp fastrpc nodes have that dt
> > property.
> >
> > 2. In the `fastrpc_rpmsg_probe()` function, it is commented that,
> >
> > "Unsigned PD offloading is only supported on CDSP"
> >
> > Does this mean adsp and sdsp shouldn't have the `qcom,non-secure-domain`
> > dt property? In fact, it was reported that removing this dt property and
> > using the `/dev/fastrpc-sdsp-secure` node instead works fine too. Is
> > this the correct way to fix it?
> >
> > I don't know much about fastrpc, just reporting the issue and guessing
> > here. It would be really if this can be fixed before the stable release.
>
> I will be glad to revert it, what was the git id for this in the tree
> now?
>
> thanks,
>
> greg k-h