[PATCH v3] xfrm: hold dev ref until after transport_finish NF_HOOK

[Qi Tang <tpluszz77@gmail.com>]

After async crypto completes, xfrm_input_resume() calls dev_put()
immediately on re-entry before the skb reaches transport_finish.
The skb->dev pointer is then used inside NF_HOOK and its okfn,
which can race with device teardown.

Remove the dev_put from the async resumption entry and instead
drop the reference after the NF_HOOK call in transport_finish,
using a saved device pointer since NF_HOOK may consume the skb.
This covers NF_DROP, NF_QUEUE and NF_STOLEN paths that skip
the okfn.

For non-transport exits (decaps, gro, drop) and secondary
async return points, release the reference inline when
async is set.

Suggested-by: Florian Westphal <fw@strlen.de>
Fixes: acf568ee859f ("xfrm: Reinject transport-mode packets through tasklet")
Cc: stable@vger.kernel.org
Signed-off-by: Qi Tang <tpluszz77@gmail.com>
---
Changes in v3:
  - Drop refcount after NF_HOOK instead of in async okfn variant
    (Florian, Steffen)
  - Remove xfrm_trans_cb.dev_held, async okfn variants, and
    xfrm_trans_queue_net parameter change from v2

Changes in v2:
  - Reuse existing dev_hold, delay dev_put instead of adding
    extra hold/put pair (Steffen)

Link: https://lore.kernel.org/netdev/20260331092737.1937-1-tpluszz77@gmail.com/ (v2)
Link: https://lore.kernel.org/all/20260320073023.21873-1-tpluszz77@gmail.com/ (v1)
---
 net/ipv4/xfrm4_input.c |  5 ++++-
 net/ipv6/xfrm6_input.c |  5 ++++-
 net/xfrm/xfrm_input.c  | 18 ++++++++++++++----
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/xfrm4_input.c b/net/ipv4/xfrm4_input.c
index f28cfd88eaf5..c2eac844bcdb 100644
--- a/net/ipv4/xfrm4_input.c
+++ b/net/ipv4/xfrm4_input.c
@@ -50,6 +50,7 @@ int xfrm4_transport_finish(struct sk_buff *skb, int async)
 {
 	struct xfrm_offload *xo = xfrm_offload(skb);
 	struct iphdr *iph = ip_hdr(skb);
+	struct net_device *dev = skb->dev;
 
 	iph->protocol = XFRM_MODE_SKB_CB(skb)->protocol;
 
@@ -73,8 +74,10 @@ int xfrm4_transport_finish(struct sk_buff *skb, int async)
 	}
 
 	NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING,
-		dev_net(skb->dev), NULL, skb, skb->dev, NULL,
+		dev_net(dev), NULL, skb, dev, NULL,
 		xfrm4_rcv_encap_finish);
+	if (async)
+		dev_put(dev);
 	return 0;
 }
 
diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c
index 9005fc156a20..699a001ac166 100644
--- a/net/ipv6/xfrm6_input.c
+++ b/net/ipv6/xfrm6_input.c
@@ -43,6 +43,7 @@ static int xfrm6_transport_finish2(struct net *net, struct sock *sk,
 int xfrm6_transport_finish(struct sk_buff *skb, int async)
 {
 	struct xfrm_offload *xo = xfrm_offload(skb);
+	struct net_device *dev = skb->dev;
 	int nhlen = -skb_network_offset(skb);
 
 	skb_network_header(skb)[IP6CB(skb)->nhoff] =
@@ -68,8 +69,10 @@ int xfrm6_transport_finish(struct sk_buff *skb, int async)
 	}
 
 	NF_HOOK(NFPROTO_IPV6, NF_INET_PRE_ROUTING,
-		dev_net(skb->dev), NULL, skb, skb->dev, NULL,
+		dev_net(dev), NULL, skb, dev, NULL,
 		xfrm6_transport_finish2);
+	if (async)
+		dev_put(dev);
 	return 0;
 }
 
diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index dc1312ed5a09..f65291eba1f6 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -506,7 +506,6 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 		/* An encap_type of -1 indicates async resumption. */
 		if (encap_type == -1) {
 			async = 1;
-			dev_put(skb->dev);
 			seq = XFRM_SKB_CB(skb)->seq.input.low;
 			spin_lock(&x->lock);
 			goto resume;
@@ -659,8 +658,11 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 			dev_hold(skb->dev);
 
 			nexthdr = x->type->input(x, skb);
-			if (nexthdr == -EINPROGRESS)
+			if (nexthdr == -EINPROGRESS) {
+				if (async)
+					dev_put(skb->dev);
 				return 0;
+			}
 
 			dev_put(skb->dev);
 			spin_lock(&x->lock);
@@ -695,9 +697,11 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 		XFRM_MODE_SKB_CB(skb)->protocol = nexthdr;
 
 		err = xfrm_inner_mode_input(x, skb);
-		if (err == -EINPROGRESS)
+		if (err == -EINPROGRESS) {
+			if (async)
+				dev_put(skb->dev);
 			return 0;
-		else if (err) {
+		} else if (err) {
 			XFRM_INC_STATS(net, LINUX_MIB_XFRMINSTATEMODEERROR);
 			goto drop;
 		}
@@ -734,6 +738,8 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 			sp->olen = 0;
 		if (skb_valid_dst(skb))
 			skb_dst_drop(skb);
+		if (async)
+			dev_put(skb->dev);
 		gro_cells_receive(&gro_cells, skb);
 		return 0;
 	} else {
@@ -753,6 +759,8 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 				sp->olen = 0;
 			if (skb_valid_dst(skb))
 				skb_dst_drop(skb);
+			if (async)
+				dev_put(skb->dev);
 			gro_cells_receive(&gro_cells, skb);
 			return err;
 		}
@@ -763,6 +771,8 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 drop_unlock:
 	spin_unlock(&x->lock);
 drop:
+	if (async)
+		dev_put(skb->dev);
 	xfrm_rcv_cb(skb, family, x && x->type ? x->type->proto : nexthdr, -1);
 	kfree_skb(skb);
 	return 0;
-- 
2.43.0