[v2] misc: fastrpc: Fix a Use after-free-bug by race condition

From: Sangsup lee <k1rh4.lee@gmail.com>

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.

Signed-off-by: Sangsup lee <k1rh4.lee@gmail.com>
---
 V1 -> V2: moving the locking to ioctl.

 drivers/misc/fastrpc.c | 2 ++
 1 file changed, 2 insertions(+)

Is there any comment for this issue?
(reference: https://www.spinics.net/lists/kernel/msg4731408.html)


2023년 3월 23일 (목) 오전 10:37, Sangsup Lee <k1rh4.lee@gmail.com>님이 작성:
>
> From: Sangsup lee <k1rh4.lee@gmail.com>
>
> 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.
>
> Signed-off-by: Sangsup lee <k1rh4.lee@gmail.com>
> ---
>  V1 -> V2: moving the locking to ioctl.
>
>  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
>

I reported fastrpc bug in
Feb,2023.(https://lore.kernel.org/lkml/20230216014120.3110-1-k1rh4.lee@gmail.com)

And Srinivas recommended this patch code for patch v2.
That's why I sent this patch v2 however, I haven't received any reply
after that.

I just want to know the next step for patching this code.
Should I just keep waiting ? Or Please let me know if I need to
provide you with more information.

(Ps. I'm sorry, i re-send this reply because of missing text-mode )

Best regards.

2023년 4월 27일 (목) 오후 6:52, Greg Kroah-Hartman <gregkh@linuxfoundation.org>님이 작성:
>
> On Thu, Apr 27, 2023 at 06:29:16PM +0900, sangsup lee wrote:
> > Is there any comment for this issue?
>
> What issue?
>
> > (reference: https://www.spinics.net/lists/kernel/msg4731408.html)
>
> Please use lore.kernel.org links, we have no control over any other
> random email archive .
>
> And the above link just points to this proposed patch.
>
> >
> >
> > 2023년 3월 23일 (목) 오전 10:37, Sangsup Lee <k1rh4.lee@gmail.com>님이 작성:
> > >
> > > From: Sangsup lee <k1rh4.lee@gmail.com>
> > >
> > > 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.
>
> How was this tested?
>
> > >
> > > Signed-off-by: Sangsup lee <k1rh4.lee@gmail.com>
> > > ---
> > >  V1 -> V2: moving the locking to ioctl.
> > >
> > >  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);
>
> Are you sure you can call this function with the lock?  If so, why isn't
> the mmap ioctl also locked?
>
> thanks,
>
> greg k-h

A: http://en.wikipedia.org/wiki/Top_post
Q: Were do I find info about this thing called top-posting?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

On Thu, Apr 27, 2023 at 08:51:48PM +0900, sangsup lee wrote:
> I reported fastrpc bug in
> Feb,2023.(https://lore.kernel.org/lkml/20230216014120.3110-1-k1rh4.lee@gmail.com)

That was a patch, not a bug report.  How was this tested?

> And Srinivas recommended this patch code for patch v2.
> That's why I sent this patch v2 however, I haven't received any reply
> after that.
> 
> I just want to know the next step for patching this code.
> Should I just keep waiting ? Or Please let me know if I need to
> provide you with more information.

Please read my comments on my last email on the patch for what you need
to address.

thanks,

greg k-h

I apologize for recognizing the email in the TOP POST format. I missed
the comment in the previous email.

2023년 4월 27일 (목) 오후 6:52, Greg Kroah-Hartman <gregkh@linuxfoundation.org>님이 작성:
>
> On Thu, Apr 27, 2023 at 06:29:16PM +0900, sangsup lee wrote:
> > Is there any comment for this issue?
>
> What issue?
>
> > (reference: https://www.spinics.net/lists/kernel/msg4731408.html)
>
> Please use lore.kernel.org links, we have no control over any other
> random email archive .
>
> And the above link just points to this proposed patch.
>
> >
> >
> > 2023년 3월 23일 (목) 오전 10:37, Sangsup Lee <k1rh4.lee@gmail.com>님이 작성:
> > >
> > > From: Sangsup lee <k1rh4.lee@gmail.com>
> > >
> > > 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.
>
> How was this tested?
>

I was unable to configure the environment in which this code is running.
Therefore, I could not go through dynamic testing for the related issue.
However, I found vulnerabilities in similar types of functions
in other drivers in the mobile environment, so I think this code is
also problematic.

> > >
> > > Signed-off-by: Sangsup lee <k1rh4.lee@gmail.com>
> > > ---
> > >  V1 -> V2: moving the locking to ioctl.
> > >
> > >  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);
>
> Are you sure you can call this function with the lock?  If so, why isn't
> the mmap ioctl also locked?

I am convinced that FASTRPC_IOCTL_MUNMAP can lead to a race condition bug.
However, as I mentioned in patch v1, I am not an expert in fastrpc.
I worried about the side effects of the code I suggested.
So, I asked you to recommend which code to use, and this is the code
that was recommended to me.
And I didn't check the mmap function because I couldn't find a bug in mmap.

>
> thanks,
>
> greg k-h