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

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Date:   Wed, 22 Mar 2023 10:59:32 +0900
From:   sangsup lee <k1rh4.lee@...il.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Amol Maheshwari <amahesh@....qualcomm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc: fastrpc: Fix a Use after-free-bug by race condition

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@...il.com>
---
 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@...aro.org>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@...il.com>
> > ---
> >   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)