[PATCH net] gve: Clear napi->skb before dev_kfree_skb_any()

[PATCH net] gve: Clear napi->skb before dev_kfree_skb_any()

[Ziwei Xiao]

gve_rx_free_skb incorrectly leaves napi->skb referencing an skb after it
is freed with dev_kfree_skb_any(). This can result in a subsequent call
to napi_get_frags returning a dangling pointer.

Fix this by clearing napi->skb before the skb is freed.

Fixes: 9b8dd5e5ea48 ("gve: DQO: Add RX path")
Cc: stable@vger.kernel.org
Reported-by: Shailend Chand <shailend@google.com>
Signed-off-by: Ziwei Xiao <ziweixiao@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Reviewed-by: Shailend Chand <shailend@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
---
 drivers/net/ethernet/google/gve/gve_rx_dqo.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_rx_dqo.c b/drivers/net/ethernet/google/gve/gve_rx_dqo.c
index c1c912de59c7..1154c1d8f66f 100644
--- a/drivers/net/ethernet/google/gve/gve_rx_dqo.c
+++ b/drivers/net/ethernet/google/gve/gve_rx_dqo.c
@@ -647,11 +647,13 @@ static void gve_rx_skb_hash(struct sk_buff *skb,
 	skb_set_hash(skb, le32_to_cpu(compl_desc->hash), hash_type);
 }
 
-static void gve_rx_free_skb(struct gve_rx_ring *rx)
+static void gve_rx_free_skb(struct napi_struct *napi, struct gve_rx_ring *rx)
 {
 	if (!rx->ctx.skb_head)
 		return;
 
+	if (rx->ctx.skb_head == napi->skb)
+		napi->skb = NULL;
 	dev_kfree_skb_any(rx->ctx.skb_head);
 	rx->ctx.skb_head = NULL;
 	rx->ctx.skb_tail = NULL;
@@ -950,7 +952,7 @@ int gve_rx_poll_dqo(struct gve_notify_block *block, int budget)
 
 		err = gve_rx_dqo(napi, rx, compl_desc, complq->head, rx->q_num);
 		if (err < 0) {
-			gve_rx_free_skb(rx);
+			gve_rx_free_skb(napi, rx);
 			u64_stats_update_begin(&rx->statss);
 			if (err == -ENOMEM)
 				rx->rx_skb_alloc_fail++;
@@ -993,7 +995,7 @@ int gve_rx_poll_dqo(struct gve_notify_block *block, int budget)
 
 		/* gve_rx_complete_skb() will consume skb if successful */
 		if (gve_rx_complete_skb(rx, napi, compl_desc, feat) != 0) {
-			gve_rx_free_skb(rx);
+			gve_rx_free_skb(napi, rx);
 			u64_stats_update_begin(&rx->statss);
 			rx->rx_desc_err_dropped_pkt++;
 			u64_stats_update_end(&rx->statss);
-- 
2.45.2.505.gda0bf45e8d-goog

Re: [PATCH net] gve: Clear napi->skb before dev_kfree_skb_any()

[Jakub Kicinski]

On Wed, 12 Jun 2024 00:16:54 +0000 Ziwei Xiao wrote:
> +	if (rx->ctx.skb_head == napi->skb)
> +		napi->skb = NULL;

There doesn't seem to be much precedent for directly poking at this
field in drivers but I don't have any better ideas..

Re: [PATCH net] gve: Clear napi->skb before dev_kfree_skb_any()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 12 Jun 2024 00:16:54 +0000 you wrote:
> gve_rx_free_skb incorrectly leaves napi->skb referencing an skb after it
> is freed with dev_kfree_skb_any(). This can result in a subsequent call
> to napi_get_frags returning a dangling pointer.
> 
> Fix this by clearing napi->skb before the skb is freed.
> 
> Fixes: 9b8dd5e5ea48 ("gve: DQO: Add RX path")
> Cc: stable@vger.kernel.org
> Reported-by: Shailend Chand <shailend@google.com>
> Signed-off-by: Ziwei Xiao <ziweixiao@google.com>
> Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
> Reviewed-by: Shailend Chand <shailend@google.com>
> Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
> 
> [...]

Here is the summary with links:
  - [net] gve: Clear napi->skb before dev_kfree_skb_any()
    https://git.kernel.org/netdev/net/c/6f4d93b78ade

You are awesome, thank you!
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