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References: <20190410193747.25302-1-jglisse@redhat.com>
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From:   Steve French <smfrench@gmail.com>
Date:   Wed, 10 Apr 2019 21:47:01 -0500
Message-ID: <CAH2r5ms-Y3FWhrabPEFt7T8MvC8Pwi1jjPFS7viWWRzx5rbVDw@mail.gmail.com>
Subject: Re: [PATCH] cifs: fix page reference leak with readv/writev
To:     jglisse@redhat.com
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Steve French <sfrench@samba.org>,
        CIFS <linux-cifs@vger.kernel.org>,
        samba-technical <samba-technical@lists.samba.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Stable <stable@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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How was this discovered? Does it address a reported user problem?

On Wed, Apr 10, 2019 at 2:38 PM <jglisse@redhat.com> wrote:
>
> From: J=C3=A9r=C3=B4me Glisse <jglisse@redhat.com>
>
> CIFS can leak pages reference gotten through GUP (get_user_pages*()
> through iov_iter_get_pages()). This happen if cifs_send_async_read()
> or cifs_write_from_iter() calls fail from within __cifs_readv() and
> __cifs_writev() respectively. This patch move page unreference to
> cifs_aio_ctx_release() which will happens on all code paths this is
> all simpler to follow for correctness.
>
> Signed-off-by: J=C3=A9r=C3=B4me Glisse <jglisse@redhat.com>
> Cc: Steve French <sfrench@samba.org>
> Cc: linux-cifs@vger.kernel.org
> Cc: samba-technical@lists.samba.org
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Stable <stable@vger.kernel.org>
> ---
>  fs/cifs/file.c | 15 +--------------
>  fs/cifs/misc.c | 23 ++++++++++++++++++++++-
>  2 files changed, 23 insertions(+), 15 deletions(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 89006e044973..a756a4d3f70f 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2858,7 +2858,6 @@ static void collect_uncached_write_data(struct cifs=
_aio_ctx *ctx)
>         struct cifs_tcon *tcon;
>         struct cifs_sb_info *cifs_sb;
>         struct dentry *dentry =3D ctx->cfile->dentry;
> -       unsigned int i;
>         int rc;
>
>         tcon =3D tlink_tcon(ctx->cfile->tlink);
> @@ -2922,10 +2921,6 @@ static void collect_uncached_write_data(struct cif=
s_aio_ctx *ctx)
>                 kref_put(&wdata->refcount, cifs_uncached_writedata_releas=
e);
>         }
>
> -       if (!ctx->direct_io)
> -               for (i =3D 0; i < ctx->npages; i++)
> -                       put_page(ctx->bv[i].bv_page);
> -
>         cifs_stats_bytes_written(tcon, ctx->total_len);
>         set_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(dentry->d_inode)->flags=
);
>
> @@ -3563,7 +3558,6 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx=
)
>         struct iov_iter *to =3D &ctx->iter;
>         struct cifs_sb_info *cifs_sb;
>         struct cifs_tcon *tcon;
> -       unsigned int i;
>         int rc;
>
>         tcon =3D tlink_tcon(ctx->cfile->tlink);
> @@ -3647,15 +3641,8 @@ collect_uncached_read_data(struct cifs_aio_ctx *ct=
x)
>                 kref_put(&rdata->refcount, cifs_uncached_readdata_release=
);
>         }
>
> -       if (!ctx->direct_io) {
> -               for (i =3D 0; i < ctx->npages; i++) {
> -                       if (ctx->should_dirty)
> -                               set_page_dirty(ctx->bv[i].bv_page);
> -                       put_page(ctx->bv[i].bv_page);
> -               }
> -
> +       if (!ctx->direct_io)
>                 ctx->total_len =3D ctx->len - iov_iter_count(to);
> -       }
>
>         /* mask nodata case */
>         if (rc =3D=3D -ENODATA)
> diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
> index bee203055b30..9bc0d17a9d77 100644
> --- a/fs/cifs/misc.c
> +++ b/fs/cifs/misc.c
> @@ -768,6 +768,11 @@ cifs_aio_ctx_alloc(void)
>  {
>         struct cifs_aio_ctx *ctx;
>
> +       /*
> +        * Must use kzalloc to initialize ctx->bv to NULL and ctx->direct=
_io
> +        * to false so that we know when we have to unreference pages wit=
hin
> +        * cifs_aio_ctx_release()
> +        */
>         ctx =3D kzalloc(sizeof(struct cifs_aio_ctx), GFP_KERNEL);
>         if (!ctx)
>                 return NULL;
> @@ -786,7 +791,23 @@ cifs_aio_ctx_release(struct kref *refcount)
>                                         struct cifs_aio_ctx, refcount);
>
>         cifsFileInfo_put(ctx->cfile);
> -       kvfree(ctx->bv);
> +
> +       /*
> +        * ctx->bv is only set if setup_aio_ctx_iter() was call successfu=
ly
> +        * which means that iov_iter_get_pages() was a success and thus t=
hat
> +        * we have taken reference on pages.
> +        */
> +       if (ctx->bv) {
> +               unsigned i;
> +
> +               for (i =3D 0; i < ctx->npages; i++) {
> +                       if (ctx->should_dirty)
> +                               set_page_dirty(ctx->bv[i].bv_page);
> +                       put_page(ctx->bv[i].bv_page);
> +               }
> +               kvfree(ctx->bv);
> +       }
> +
>         kfree(ctx);
>  }
>
> --
> 2.20.1
>


--=20
Thanks,

Steve