Re: [PATCH] misc: fastrpc: Fix a Use after-free-bug by race condition

[Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>]

On 22/03/2023 01:59, sangsup lee wrote:
> Sounds great.
>
> Thank you for your recommendation.
> The patch code that you recommend is clear and simple.
> Please patch this.
>
> Signed-off-by: Sangsup lee <k1rh4.lee@xxxxxxxxx>
> ---

Please follow kernel patch submission guidelines, any changes to code 
should be send as new version of patch.

Have a look at Documentation/process/submitting-patches.rst for more 
information.

thanks,
Srini
>   drivers/misc/fastrpc.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 93ebd174d848..aa1cf0e9f4ed 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1901,7 +1901,9 @@ static long fastrpc_device_ioctl(struct file
> *file, unsigned int cmd,
>                  err = fastrpc_req_mmap(fl, argp);
>                  break;
>          case FASTRPC_IOCTL_MUNMAP:
> +               mutex_lock(&fl->mutex);
>                  err = fastrpc_req_munmap(fl, argp);
> +               mutex_unlock(&fl->mutex);
>                  break;
>          case FASTRPC_IOCTL_MEM_MAP:
>                  err = fastrpc_req_mem_map(fl, argp);
> --
> 2.25.1
>
>
> 2023년 3월 21일 (화) 오후 6:27, Srinivas Kandagatla
> <srinivas.kandagatla@xxxxxxxxxx>님이 작성:
> > Thanks Sangsup for reporting the issue and sharing the patch,
> >
> > Sorry, for some reason I missed this patch.
> >
> > On 16/02/2023 01:41, Sangsup Lee wrote:
> > > This patch adds mutex_lock for fixing an Use-after-free bug.
> > > fastrpc_req_munmap_impl can be called concurrently in multi-threded environments.
> > > The buf which is allocated by list_for_each_safe can be used after another thread frees it.
> > Commit log can be improved here to something like:
> >
> > fastrcp_munmap takes two steps to unmap the memory, first to find a
> > matching fastrpc buf in the list and second is to send request to DSP to
> > unmap it.
> > There is a potentially window of race between these two operations,
> > which can lead to user-after-free.
> >
> > Fix this by adding locking around this two operations.
> >
> > > Signed-off-by: Sangsup Lee <k1rh4.lee@xxxxxxxxx>
> > > ---
> > >    drivers/misc/fastrpc.c | 7 ++++++-
> > >    1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > > index 5310606113fe..c4b5fa4a50a6 100644
> > > --- a/drivers/misc/fastrpc.c
> > > +++ b/drivers/misc/fastrpc.c
> > > @@ -1806,10 +1806,12 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
> > >        struct fastrpc_buf *buf = NULL, *iter, *b;
> > >        struct fastrpc_req_munmap req;
> > >        struct device *dev = fl->sctx->dev;
> > > +     int err;
> > >
> > >        if (copy_from_user(&req, argp, sizeof(req)))
> > >                return -EFAULT;
> > >
> > > +     mutex_lock(&fl->mutex);
> > >        spin_lock(&fl->lock);
> > >        list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
> > >                if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
> > > @@ -1822,10 +1824,13 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
> > >        if (!buf) {
> > >                dev_err(dev, "mmap\t\tpt 0x%09llx [len 0x%08llx] not in list\n",
> > >                        req.vaddrout, req.size);
> > > +             mutex_unlock(&fl->mutex);
> > >                return -EINVAL;
> > >        }
> > >
> > > -     return fastrpc_req_munmap_impl(fl, buf);
> > > +     err = fastrpc_req_munmap_impl(fl, buf);
> > > +     mutex_unlock(&fl->mutex);
> > > +     return err;
> >
> > How about moving the locking to ioctl:
> >
> > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > index a701132638cf..2f217071a6c3 100644
> > --- a/drivers/misc/fastrpc.c
> > +++ b/drivers/misc/fastrpc.c
> > @@ -2087,7 +2087,9 @@ static long fastrpc_device_ioctl(struct file
> > *file, unsigned int cmd,
> >                   err = fastrpc_req_mmap(fl, argp);
> >                   break;
> >           case FASTRPC_IOCTL_MUNMAP:
> > +               mutex_lock(&fl->mutex);
> >                   err = fastrpc_req_munmap(fl, argp);
> > +               mutex_unlock(&fl->mutex);
> >                   break;
> >           case FASTRPC_IOCTL_MEM_MAP:
> >                   err = fastrpc_req_mem_map(fl, argp);
> >
> >
> > thanks,
> > srini
> > >    }
> > >
> > >    static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)