[PATCH iwl-net 2/3] e1000e: fix ps_pages DMA map error sentinel

[Matt Vollrath <tactii@gmail.com>]

While allocating packet-split buffer pages, a failed DMA mapping would
leave DMA_MAPPING_ERROR in the ps_page->dma field.

This would have two consequences:
* The next attempt to allocate that buffer would write DMA_MAPPING_ERROR
  to h/w if all pages are allocated. If the h/w uses that buffer and is
  handling a frame large enough to touch the affected page, it would
  cause a DMA fault and be dropped. The driver would then call
  dma_unmap_page() on DMA_MAPPING_ERROR and unknowingly send the
  uninitialized page up the stack as part of the frame payload.
* On ring teardown, dma_unmap_page() would be called on
  DMA_MAPPING_ERROR.

This condition is only reachable when MTU > 1500 and PAGE_SIZE <= 16K.

Fix this by setting ps_page->dma = 0 upon mapping failure and separately
testing ->page and ->dma during allocation and teardown.

The rewrite of the ps_pages section of e1000_clean_rx_ring was necessary
to recognize the case of a mapped page without a valid DMA mapping. It
also fixes a separate bug which would potentially leak pages on ring
teardown. The cleaner stops cleaning pages when h/w reported that it did
not write to a page in the sequence, leaving the following pages
allocated and mapped. The teardown would then break early and leak the
unused mapped pages. If the ring is re-allocated with similar
configuration, it would reclaim those lost pages. This would only affect
configurations with rx_ps_pages >= 2 (MTU > PAGE_SIZE) and the same
condition of MTU > 1500 and PAGE_SIZE <= 16K.

Signed-off-by: Matt Vollrath <tactii@gmail.com>
Assisted-by: Claude:claude-5-fable
Fixes: bc7f75fa9788 ("[E1000E]: New pci-express e1000 driver (currently for ICH9 devices only)")
Cc: stable@vger.kernel.org
---
 drivers/net/ethernet/intel/e1000e/netdev.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
index 26f45ee8c7e7..063fc8cd2673 100644
--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
@@ -759,12 +759,15 @@ static void e1000_alloc_rx_buffers_ps(struct e1000_ring *rx_ring,
 					adapter->alloc_rx_buff_failed++;
 					goto no_buffers;
 				}
+			}
+			if (!ps_page->dma) {
 				ps_page->dma = dma_map_page(&pdev->dev,
 							    ps_page->page,
 							    0, PAGE_SIZE,
 							    DMA_FROM_DEVICE);
 				if (dma_mapping_error(&pdev->dev,
 						      ps_page->dma)) {
+					ps_page->dma = 0;
 					dev_err(&adapter->pdev->dev,
 						"Rx DMA page map failed\n");
 					adapter->rx_dma_failed++;
@@ -1722,13 +1725,15 @@ static void e1000_clean_rx_ring(struct e1000_ring *rx_ring)
 
 		for (j = 0; j < PS_PAGE_BUFFERS; j++) {
 			ps_page = &buffer_info->ps_pages[j];
-			if (!ps_page->page)
-				break;
-			dma_unmap_page(&pdev->dev, ps_page->dma, PAGE_SIZE,
-				       DMA_FROM_DEVICE);
-			ps_page->dma = 0;
-			put_page(ps_page->page);
-			ps_page->page = NULL;
+			if (ps_page->dma) {
+				dma_unmap_page(&pdev->dev, ps_page->dma,
+					       PAGE_SIZE, DMA_FROM_DEVICE);
+				ps_page->dma = 0;
+			}
+			if (ps_page->page) {
+				put_page(ps_page->page);
+				ps_page->page = NULL;
+			}
 		}
 	}
 
-- 
2.43.0