From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.prgmr.com ([71.19.149.6]:50782 "EHLO mail.prgmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753037AbeCEVKh (ORCPT ); Mon, 5 Mar 2018 16:10:37 -0500 Subject: Re: [PATCH] net/mlx4_en: fix potential use-after-free with dma_unmap_page To: Tariq Toukan , Yishai Hadas Cc: netdev@vger.kernel.org References: <1520223607-17560-1-git-send-email-srn@prgmr.com> <1cee1792-52ae-f408-15f0-ee42c1fb2ea3@mellanox.com> From: Sarah Newman Message-ID: <2a726e89-8411-380e-3809-2dd71bceb7a7@prgmr.com> Date: Mon, 5 Mar 2018 13:10:36 -0800 MIME-Version: 1.0 In-Reply-To: <1cee1792-52ae-f408-15f0-ee42c1fb2ea3@mellanox.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org List-ID: On 03/05/2018 02:09 AM, Tariq Toukan wrote: > > > On 05/03/2018 6:20 AM, Sarah Newman wrote: >> Take an additional reference to a page whenever it is placed >> into the rx ring and put the page again after running >> dma_unmap_page. >> >> When swiotlb is in use, calling dma_unmap_page means that >> the original page mapped with dma_map_page must still be valid, >> as swiotlb will copy data from its internal cache back to the >> originally requested DMA location. >> >> When GRO is enabled, before this patch all references to the >> original frag may be put and the page freed before dma_unmap_page >> in mlx4_en_free_frag is called. >> >> It is possible there is a path where the use-after-free occurs >> even with GRO disabled, but this has not been observed so far. >> >> The bug can be trivially detected by doing the following: >> >> * Compile the kernel with DEBUG_PAGEALLOC >> * Run the kernel as a Xen Dom0 >> * Leave GRO enabled on the interface >> * Run a 10 second or more test with iperf over the interface. >> > > Hi Sarah, thanks for your patch! > >> This bug was likely introduced in >> commit 4cce66cdd14a ("mlx4_en: map entire pages to increase throughput"), >> first part of u3.6. >> >> It was incidentally fixed in >> commit 34db548bfb95 ("mlx4: add page recycling in receive path"), >> first part of v4.12. >> >> This version applies to the v4.9 series. >> >> Signed-off-by: Sarah Newman >> Tested-by: Sarah Newman >> --- >>   drivers/net/ethernet/mellanox/mlx4/en_rx.c   | 39 +++++++++++++++++++++------- >>   drivers/net/ethernet/mellanox/mlx4/en_tx.c   |  3 ++- >>   drivers/net/ethernet/mellanox/mlx4/mlx4_en.h |  1 + >>   3 files changed, 32 insertions(+), 11 deletions(-) >> >> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c >> index bcbb80f..d1fb087 100644 >> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c >> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c >> @@ -80,10 +80,14 @@ static int mlx4_alloc_pages(struct mlx4_en_priv *priv, >>       page_alloc->page = page; >>       page_alloc->dma = dma; >>       page_alloc->page_offset = 0; >> +    page_alloc->page_owner = true; > > Do we really need this boolean? I believe the issue can be fixed without it. We need to make sure we hold the correct refcnt at every stage, and > maintain symmetry between a flow and its inverse. The reason this was added is because the page address needs to stay around until after dma unmap_page is called, and right now setting page to NULL is used to indicate that put_page should not be called when frags are freed in mlx4_en_free_frag. So either the code needs to be rearranged so that dma_unmap_page while page is still set, or some variable needed to be used to indicate whether put_page should be called when the frags are freed. If dma_unmap_page was called before page was set to NULL, then this variable doesn't need to be added, yes. Then the call to dma_unmap_page in mlx4_en_free_frag would also be contingent on frags[i].page being set. There are two places where page is set to NULL without calling dma_unmap_page first, mlx4_en_complete_rx_desc and mlx4_en_xmit_frame. Is mlx4_en_complete_rx_desc the only place where a call to dma_unmap_page would need to be added? The other place page is set to NULL without a call to dma_unmap_page first is in mlx4_en_xmit_frame, and I believe there is no call to mlx4_en_free_frag if mlx4_en_xmit_frame executes. > > Upon alloc, refcnt is 1. This alloc refcnt should be inverted by a call to put_page. We might want to introduce a page free API (symmetric to > mlx4_alloc_pages), that does: dma unmap the page, call put_page, nullify pointer. That seems reasonable. > Once alloced, page refcnt is bumped up by the amount of possible frags populating it, which is (page_size / frag_stride), as you do here. > >>       /* Not doing get_page() for each frag is a big win >>        * on asymetric workloads. Note we can not use atomic_set(). >>        */ >> -    page_ref_add(page, page_alloc->page_size / frag_info->frag_stride - 1); >> +    /* Since the page must be valid until after dma_unmap_page is called, >> +     * take an additional reference we would not have otherwise. >> +     */ >> +    page_ref_add(page, page_alloc->page_size / frag_info->frag_stride); >>       return 0; >>   } >>   @@ -105,9 +109,13 @@ static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv, >>           page_alloc[i].page_offset += frag_info->frag_stride; >>             if (page_alloc[i].page_offset + frag_info->frag_stride <= >> -            ring_alloc[i].page_size) >> -            continue; >> - >> +            ring_alloc[i].page_size) { >> +            WARN_ON(!page_alloc[i].page); >> +            WARN_ON(!page_alloc[i].page_owner); > > Why WARN before the likely() check? > Move after the check, for a better performance. No particular reason. > >> +            if (likely(page_alloc[i].page && >> +                   page_alloc[i].page_owner)) >> +                continue; >> +        } >>           if (unlikely(mlx4_alloc_pages(priv, &page_alloc[i], >>                             frag_info, gfp))) >>               goto out; >> @@ -131,7 +139,7 @@ static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv, >>               page = page_alloc[i].page; >>               /* Revert changes done by mlx4_alloc_pages */ >>               page_ref_sub(page, page_alloc[i].page_size / >> -                       priv->frag_info[i].frag_stride - 1); >> +                       priv->frag_info[i].frag_stride); >>               put_page(page); >>           } >>       } >> @@ -146,11 +154,13 @@ static void mlx4_en_free_frag(struct mlx4_en_priv *priv, >>       u32 next_frag_end = frags[i].page_offset + 2 * frag_info->frag_stride; >>     -    if (next_frag_end > frags[i].page_size) >> +    if (next_frag_end > frags[i].page_size) { >>           dma_unmap_page(priv->ddev, frags[i].dma, frags[i].page_size, >>                      frag_info->dma_dir); >> +        put_page(frags[i].page); >> +    } >>   -    if (frags[i].page) >> +    if (frags[i].page_owner) >>           put_page(frags[i].page); >>   } >>   @@ -184,9 +194,10 @@ static int mlx4_en_init_allocator(struct mlx4_en_priv *priv, >>           page = page_alloc->page; >>           /* Revert changes done by mlx4_alloc_pages */ >>           page_ref_sub(page, page_alloc->page_size / >> -                   priv->frag_info[i].frag_stride - 1); >> +                   priv->frag_info[i].frag_stride); >>           put_page(page); >>           page_alloc->page = NULL; >> +        page_alloc->page_owner = false; >>       } >>       return -ENOMEM; >>   } >> @@ -206,12 +217,14 @@ static void mlx4_en_destroy_allocator(struct mlx4_en_priv *priv, >>             dma_unmap_page(priv->ddev, page_alloc->dma, >>                   page_alloc->page_size, frag_info->dma_dir); >> +        put_page(page_alloc->page); > > for symmetry, i'd move this after the while loop. Or use the wrapper function you suggested for dma_unmap_page? > >>           while (page_alloc->page_offset + frag_info->frag_stride < >>                  page_alloc->page_size) { >>               put_page(page_alloc->page); >>               page_alloc->page_offset += frag_info->frag_stride; >>           } >>           page_alloc->page = NULL; >> +        page_alloc->page_owner = false; >>       } >>   } >>   @@ -251,6 +264,11 @@ static int mlx4_en_prepare_rx_desc(struct mlx4_en_priv *priv, >>       if (ring->page_cache.index > 0) { >>           frags[0] = ring->page_cache.buf[--ring->page_cache.index]; >>           rx_desc->data[0].addr = cpu_to_be64(frags[0].dma); >> +        WARN_ON(frags[0].page_owner); >> +        if (likely(!frags[0].page_owner)) { >> +            page_ref_inc(frags[0].page); >> +            frags[0].page_owner = true; >> +        } > > Why? If I'm not mistaken, the page is cached with refcnt == 2. No? In mlx4_en_deactivate_rx_ring, pages assigned to frames in the page_cache are only put once. If refcnt == 2 when it's inserted, isn't that a memory leak? I can confirm one way or another if you haven't already. > >>           return 0; >>       } >>   @@ -569,6 +587,7 @@ void mlx4_en_deactivate_rx_ring(struct mlx4_en_priv *priv, >>             dma_unmap_page(priv->ddev, frame->dma, frame->page_size, >>                      priv->frag_info[0].dma_dir); >> +        WARN_ON(frame->page_owner); >>           put_page(frame->page); >>       } >>       ring->page_cache.index = 0; >> @@ -595,7 +614,7 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv, >>           frag_info = &priv->frag_info[nr]; >>           if (length <= frag_info->frag_prefix_size) >>               break; >> -        if (unlikely(!frags[nr].page)) >> +        if (unlikely(!frags[nr].page_owner)) >>               goto fail; >>             dma = be64_to_cpu(rx_desc->data[nr].addr); >> @@ -607,7 +626,7 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv, >>           skb_frag_size_set(&skb_frags_rx[nr], frag_info->frag_size); >>           skb_frags_rx[nr].page_offset = frags[nr].page_offset; >>           skb->truesize += frag_info->frag_stride; >> -        frags[nr].page = NULL; >> +        frags[nr].page_owner = false; >>       } >>       /* Adjust size of last fragment to match actual length */ >>       if (nr > 0) >> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c >> index e2509bb..25f7f9e 100644 >> --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c >> +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c >> @@ -356,6 +356,7 @@ u32 mlx4_en_recycle_tx_desc(struct mlx4_en_priv *priv, >>           .dma = tx_info->map0_dma, >>           .page_offset = 0, >>           .page_size = PAGE_SIZE, >> +        .page_owner = false, > > I don't understand why this is needed. Not strictly needed but there for clarity. > >>       }; >>         if (!mlx4_en_rx_recycle(ring->recycle_ring, &frame)) { >> @@ -1128,7 +1129,7 @@ netdev_tx_t mlx4_en_xmit_frame(struct mlx4_en_rx_alloc *frame, >>       dma = frame->dma; >>         tx_info->page = frame->page; >> -    frame->page = NULL; >> +    frame->page_owner = false; >>       tx_info->map0_dma = dma; >>       tx_info->map0_byte_count = length; >>       tx_info->nr_txbb = nr_txbb; >> diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h >> index df0f396..2c9d9a6 100644 >> --- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h >> +++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h >> @@ -261,6 +261,7 @@ struct mlx4_en_rx_alloc { >>       dma_addr_t    dma; >>       u32        page_offset; >>       u32        page_size; >> +    bool        page_owner; >>   }; >>     #define MLX4_EN_CACHE_SIZE (2 * NAPI_POLL_WEIGHT) >> > > Thanks, > Tariq Thanks, Sarah