[PATCH net 2/3] ixgbe: avoid premature Rx buffer reuse

[Björn Töpel]

From: Björn Töpel <bjorn.to...@intel.com>

The page recycle code, incorrectly, relied on that a page fragment
could not be freed inside xdp_do_redirect(). This assumption leads to
that page fragments that are used by the stack/XDP redirect can be
reused and overwritten.

To avoid this, store the page count prior invoking xdp_do_redirect().

Fixes: 6453073987ba ("ixgbe: add initial support for xdp redirect")
Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 28 ++++++++++++++-----
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c 
b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 2f8a4cfc5fa1..fb5c311d72b6 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1945,7 +1945,8 @@ static inline bool ixgbe_page_is_reserved(struct page 
*page)
        return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
-static bool ixgbe_can_reuse_rx_page(struct ixgbe_rx_buffer *rx_buffer)
+static bool ixgbe_can_reuse_rx_page(struct ixgbe_rx_buffer *rx_buffer,
+                                   int rx_buffer_pgcnt)
 {
        unsigned int pagecnt_bias = rx_buffer->pagecnt_bias;
        struct page *page = rx_buffer->page;
@@ -1956,7 +1957,7 @@ static bool ixgbe_can_reuse_rx_page(struct 
ixgbe_rx_buffer *rx_buffer)
 
 #if (PAGE_SIZE < 8192)
        /* if we are only owner of page we can reuse it */
-       if (unlikely((page_ref_count(page) - pagecnt_bias) > 1))
+       if (unlikely((rx_buffer_pgcnt - pagecnt_bias) > 1))
                return false;
 #else
        /* The last offset is a bit aggressive in that we assume the
@@ -2018,14 +2019,25 @@ static void ixgbe_add_rx_frag(struct ixgbe_ring 
*rx_ring,
 #endif
 }
 
+static int ixgbe_rx_buffer_page_count(struct ixgbe_rx_buffer *rx_buffer)
+{
+#if (PAGE_SIZE < 8192)
+       return page_count(rx_buffer->page);
+#else
+       return 0;
+#endif
+}
+
 static struct ixgbe_rx_buffer *ixgbe_get_rx_buffer(struct ixgbe_ring *rx_ring,
                                                   union ixgbe_adv_rx_desc 
*rx_desc,
                                                   struct sk_buff **skb,
-                                                  const unsigned int size)
+                                                  const unsigned int size,
+                                                  int *rx_buffer_pgcnt)
 {
        struct ixgbe_rx_buffer *rx_buffer;
 
        rx_buffer = &rx_ring->rx_buffer_info[rx_ring->next_to_clean];
+       *rx_buffer_pgcnt = ixgbe_rx_buffer_page_count(rx_buffer);
        prefetchw(rx_buffer->page);
        *skb = rx_buffer->skb;
 
@@ -2055,9 +2067,10 @@ static struct ixgbe_rx_buffer 
*ixgbe_get_rx_buffer(struct ixgbe_ring *rx_ring,
 
 static void ixgbe_put_rx_buffer(struct ixgbe_ring *rx_ring,
                                struct ixgbe_rx_buffer *rx_buffer,
-                               struct sk_buff *skb)
+                               struct sk_buff *skb,
+                               int rx_buffer_pgcnt)
 {
-       if (ixgbe_can_reuse_rx_page(rx_buffer)) {
+       if (ixgbe_can_reuse_rx_page(rx_buffer, rx_buffer_pgcnt)) {
                /* hand second half of page back to the ring */
                ixgbe_reuse_rx_page(rx_ring, rx_buffer);
        } else {
@@ -2296,6 +2309,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector 
*q_vector,
        u16 cleaned_count = ixgbe_desc_unused(rx_ring);
        unsigned int xdp_xmit = 0;
        struct xdp_buff xdp;
+       int rx_buffer_pgcnt;
 
        xdp.rxq = &rx_ring->xdp_rxq;
 
@@ -2327,7 +2341,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector 
*q_vector,
                 */
                dma_rmb();
 
-               rx_buffer = ixgbe_get_rx_buffer(rx_ring, rx_desc, &skb, size);
+               rx_buffer = ixgbe_get_rx_buffer(rx_ring, rx_desc, &skb, size, 
&rx_buffer_pgcnt);
 
                /* retrieve a buffer from the ring */
                if (!skb) {
@@ -2372,7 +2386,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector 
*q_vector,
                        break;
                }
 
-               ixgbe_put_rx_buffer(rx_ring, rx_buffer, skb);
+               ixgbe_put_rx_buffer(rx_ring, rx_buffer, skb, rx_buffer_pgcnt);
                cleaned_count++;
 
                /* place incomplete frames back on ring for completion */
-- 
2.25.1