[PATCH] sfc: potential dereference of null pointer

The return value of kcalloc() needs to be checked.
To avoid dereference of null pointer in case of the failure of alloc,
such as efx_fini_rx_recycle_ring().
Therefore, it should be better to change the definition of page_ptr_mask
to signed int and then assign the page_ptr_mask to -1 when page_ring is
NULL, in order to avoid the use in the loop in
efx_fini_rx_recycle_ring().

Fixes: 3d95b884392f ("sfc: move more rx code")
Signed-off-by: Jiasheng Jiang <redacted>
---
 drivers/net/ethernet/sfc/net_driver.h | 2 +-
 drivers/net/ethernet/sfc/rx_common.c  | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index 9b4b25704271..beba3e0a6027 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h

@@ -407,7 +407,7 @@ struct efx_rx_queue {
 	unsigned int page_recycle_count;
 	unsigned int page_recycle_failed;
 	unsigned int page_recycle_full;
-	unsigned int page_ptr_mask;
+	int page_ptr_mask;
 	unsigned int max_fill;
 	unsigned int fast_fill_trigger;
 	unsigned int min_fill;

diff --git a/drivers/net/ethernet/sfc/rx_common.c b/drivers/net/ethernet/sfc/rx_common.c
index 68fc7d317693..d9d0a5805f1c 100644
--- a/drivers/net/ethernet/sfc/rx_common.c
+++ b/drivers/net/ethernet/sfc/rx_common.c

@@ -150,7 +150,10 @@ static void efx_init_rx_recycle_ring(struct efx_rx_queue *rx_queue)
 					    efx->rx_bufs_per_page);
 	rx_queue->page_ring = kcalloc(page_ring_size,
 				      sizeof(*rx_queue->page_ring), GFP_KERNEL);
-	rx_queue->page_ptr_mask = page_ring_size - 1;
+	if (!rx_queue->page_ring)
+		rx_queue->page_ptr_mask = -1;
+	else
+		rx_queue->page_ptr_mask = page_ring_size - 1;
 }
 
 static void efx_fini_rx_recycle_ring(struct efx_rx_queue *rx_queue)

-- 
2.25.1

On Thu, 16 Dec 2021 16:49:02 +0800 Jiasheng Jiang wrote:

[PATCH] sfc: potential dereference of null pointer

Please give the commit a more unique name.

The return value of kcalloc() needs to be checked.
To avoid dereference of null pointer in case of the failure of alloc,
such as efx_fini_rx_recycle_ring().
Therefore, it should be better to change the definition of page_ptr_mask
to signed int and then assign the page_ptr_mask to -1 when page_ring is
NULL, in order to avoid the use in the loop in
efx_fini_rx_recycle_ring().

What about uses of this ring, you mention avoiding null-deref in the
freeing function but presumably something is actually using this ring
at runtime. Seems like we should return -ENOMEM.

Fixes: 3d95b884392f ("sfc: move more rx code")

Moving buggy code does not introduce the problem, please find a Fixes
tag referring to where the bad code was _introduced_.