linux-kernel - Re: [PATCH 1/4] staging: kpc2000: Unpin partial pinned pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAFqt6zYHXmoCrWLEru2FZsRnXptFERJv1qiDFPip=q_cZaZEBg@mail.gmail.com>
Date:   Wed, 17 Jun 2020 23:13:32 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, jane.pnx9@...il.com,
        pakki001@....edu, ldufour@...ux.ibm.com, harshjain32@...il.com,
        Simon Sandström <simon@...anor.nu>,
        Michel Lespinasse <walken@...gle.com>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        linux-kernel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Bharath Vedartham <linux.bhar@...il.com>
Subject: Re: [PATCH 1/4] staging: kpc2000: Unpin partial pinned pages

On Wed, Jun 17, 2020 at 4:43 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> On Wed, Jun 17, 2020 at 07:57:20AM +0530, Souptick Joarder wrote:
> > There is a bug, when get_user_pages() failed but partially pinned
> > pages are not unpinned. Fixed it.
> >
> > Also, int is more appropriate type for rv. Changed it.
> >
> > Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Cc: Bharath Vedartham <linux.bhar@...il.com>
> > Cc: Dan Carpenter <dan.carpenter@...cle.com>
> > ---
> >  drivers/staging/kpc2000/kpc_dma/fileops.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c b/drivers/staging/kpc2000/kpc_dma/fileops.c
> > index 8975346..b136353 100644
> > --- a/drivers/staging/kpc2000/kpc_dma/fileops.c
> > +++ b/drivers/staging/kpc2000/kpc_dma/fileops.c
> > @@ -35,7 +35,7 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
> >                           unsigned long iov_base, size_t iov_len)
> >  {
> >       unsigned int i = 0;
> > -     long rv = 0;
> > +     int rv = 0;
> >       struct kpc_dma_device *ldev;
> >       struct aio_cb_data *acd;
> >       DECLARE_COMPLETION_ONSTACK(done);
> > @@ -193,6 +193,10 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
> >               put_page(acd->user_pages[i]);
>                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> >   err_get_user_pages:
> > +     if (rv > 0) {
> > +             for (i = 0; i < rv; i++)
> > +                     put_pages(acd->user_pages[i])
>                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> > +     }
>
> This isn't a complete fix.  "rv" is the negative error code but here we
> are returning a positive value on this path.

In case of error of get_user_pages(), it will return -errno, 0 and 3rd one is
(rv > 0 && rv != acd->page_count). When rv is -errno or 0 there is no need
to call put_pages() in error path. But for 3rd case partially mapped pages
need to unpin.

Correct me if I am missing anything.

>Also it's ugly to have
> same put_page() loop repeated twice.

Yes, I agree, but these are intermediate steps. Patch [4/4] of this series
finally did the same.

>
> It would be better to write it like this:
>
>         rv = get_user_pages(iov_base, acd->page_count, FOLL_TOUCH | FOLL_WRITE | FOLL_GET, acd->user_pages, NULL);
>         mmap_read_unlock(current->mm);        /*  release the semaphore */
>         if (rv < 0)
>                 goto free_pages;
>         if (rv != acd->page_count) {
>                 acd->page_count = rv;
>                 rv = -EFAULT;
>                 goto put_pages;
>         }
>
>         ...
>
> put_pages:
>         for (i = 0 ; i < acd->page_count ; i++)
>                 put_pages(acd->user_pages[i]);
> free_pages:
>         kfree(acd->user_pages);
>
> regards,
> dan carpenter
>