Re: [PATCH] cifs: fix page reference leak with readv/writev

[Steve French]

How was this discovered? Does it address a reported user problem?

On Wed, Apr 10, 2019 at 2:38 PM <jglisse@xxxxxxxxxx> wrote:
>
> From: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
>
> 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: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
> Cc: Steve French <sfrench@xxxxxxxxx>
> Cc: linux-cifs@xxxxxxxxxxxxxxx
> Cc: samba-technical@xxxxxxxxxxxxxxx
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Stable <stable@xxxxxxxxxxxxxxx>
> ---
>  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 = ctx->cfile->dentry;
> -       unsigned int i;
>         int rc;
>
>         tcon = tlink_tcon(ctx->cfile->tlink);
> @@ -2922,10 +2921,6 @@ static void collect_uncached_write_data(struct cifs_aio_ctx *ctx)
>                 kref_put(&wdata->refcount, cifs_uncached_writedata_release);
>         }
>
> -       if (!ctx->direct_io)
> -               for (i = 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 = &ctx->iter;
>         struct cifs_sb_info *cifs_sb;
>         struct cifs_tcon *tcon;
> -       unsigned int i;
>         int rc;
>
>         tcon = tlink_tcon(ctx->cfile->tlink);
> @@ -3647,15 +3641,8 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
>                 kref_put(&rdata->refcount, cifs_uncached_readdata_release);
>         }
>
> -       if (!ctx->direct_io) {
> -               for (i = 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 = ctx->len - iov_iter_count(to);
> -       }
>
>         /* mask nodata case */
>         if (rc == -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 within
> +        * cifs_aio_ctx_release()
> +        */
>         ctx = 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 successfuly
> +        * which means that iov_iter_get_pages() was a success and thus that
> +        * we have taken reference on pages.
> +        */
> +       if (ctx->bv) {
> +               unsigned i;
> +
> +               for (i = 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
>


-- 
Thanks,

Steve