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SubjectRe: [PATCH] cifs: fix page reference leak with readv/writev
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: Jérôme 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: Jérôme 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 = 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

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