[PATCH net v4 0/3] xfrm: fix vti tunnel device use-after-free across async crypto resumption

[PATCH net v4 0/3] xfrm: fix vti tunnel device use-after-free across async crypto resumption

[Qihang]

This replaces the v1/v2 vti/vti6 series and the earlier reference-transfer
rework.

vti_input() and vti6_input_proto() cache the tunnel pointer in the skb
control buffer without taking a reference.  With async crypto the
receive callback runs from the crypto completion, after a possible
device teardown, and dereferences the freed tunnel device.

The input hook takes a reference on the tunnel device when it caches
the tunnel.  A successful receive callback leaves the cached tunnel in
place; xfrm_input() releases the reference on every exit, including
after delivery and on the drop paths.  The error callback only updates
the counters, so the common drop path releases the reference after the
skb has been freed.  IPTFS, which frees the outer skb itself, releases
it through xfrm_input_drop()/xfrm_input_consume().

Patch 3 depends on the first two: it releases the tunnel reference from
the drop path, which needs the receive callback ordering and the address
family set up by patches 1 and 2.

Changes since v3:
- the cached pointer is always a tunnel; the address family selects its
  type, and a non-NULL slot means one device reference is held, so a
  nested or pre-installed tunnel device cannot leak it
- xfrm_input() takes the device out of the skb before
  gro_cells_receive()/transport_finish(), which may consume the skb
- the device reference is dropped only after the skb has been freed,
  including on the error path
- IPTFS passes the state's address family explicitly instead of
  inferring it from the secpath; the consumed skb keeps consume_skb()
  semantics and the drop paths keep their skb drop reason
- drop the xfrmi changes: it re-looks-up the interface and does not
  take part in the reference transfer
- merge the reference and IPTFS changes into one patch so the series
  stays bisectable
- the gro_cells NAPI window is pre-existing and is documented, not
  changed

Runtime evidence (KASAN, aarch64 QEMU):
- VTI async success and error: RTM_DELLINK completes without a KASAN
  report; the unfixed tree reports slab-use-after-free in vti_rcv_cb.
- Async resume with the SA deleted in the crypto window: the reference
  is released and the device is removed; with patch 2 reverted,
  xfrm_input_take_tunnel_dev() warns and unregister_netdevice() waits
  for vti0.
- IPTFS outer-skb free: RTM_DELLINK completes; with the !first_skb
  xfrm_input_drop() reverted to kfree_skb(), the reference leaks and
  unregister_netdevice() waits for vti0.
The IPTFS timer/reorder/state-teardown paths are covered by code audit,
not by a runtime trigger.

Previous versions:
  https://lore.kernel.org/netdev/20261013074610.17808-1-q.h.hack.winter@gmail.com/ (v2)
  https://lore.kernel.org/netdev/20260930090813.73901-1-q.h.hack.winter@gmail.com/ (v1)

Qihang


Qihang (3):
  xfrm: run the receive callback before dropping the skb->dev reference
  xfrm: set the address family before the early invalid-state drop
  xfrm: hold the tunnel device reference across the input path

 net/ipv4/ip_vti.c      |  3 ++
 net/ipv6/ip6_vti.c     |  4 +++
 net/ipv6/xfrm6_input.c |  3 ++
 net/xfrm/xfrm_inout.h  |  4 +++
 net/xfrm/xfrm_input.c  | 74 +++++++++++++++++++++++++++++++++++++++---
 net/xfrm/xfrm_iptfs.c  | 25 +++++++++-----
 6 files changed, 99 insertions(+), 14 deletions(-)

-- 
2.54.0 (Apple Git-157)

[PATCH net v4 1/3] xfrm: run the receive callback before dropping the skb->dev reference

[Qihang]

The drop path in xfrm_input() releases the skb->dev reference that is
held across an async resumption before it runs the receive callbacks.
The callbacks may still dereference skb->dev, xfrmi_rcv_cb() reads
skb->dev->ifindex, so they can race a concurrent teardown of the
device.  Run the callbacks first and drop the reference afterwards,
like the success path does.

The early drop for a state that is no longer valid releases the
reference on its own; let the drop label handle that reference too.

Fixes: 1c428b038400 ("xfrm: hold dev ref until after transport_finish NF_HOOK")
Cc: stable@vger.kernel.org
Signed-off-by: Qihang <q.h.hack.winter@gmail.com>
---
 net/xfrm/xfrm_input.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 5ed87d51392a..94de4f698c33 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -496,7 +496,7 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 					       LINUX_MIB_XFRMINSTATEINVALID);
 
 			if (encap_type == -1)
-				dev_put(dev);
+				async = 1;
 			goto drop;
 		}
 
@@ -779,9 +779,9 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 drop_unlock:
 	spin_unlock(&x->lock);
 drop:
+	xfrm_rcv_cb(skb, family, xfrm_proto, -1);
 	if (async)
 		dev_put(dev);
-	xfrm_rcv_cb(skb, family, xfrm_proto, -1);
 	kfree_skb(skb);
 	return 0;
 }
-- 
2.54.0 (Apple Git-157)

[PATCH net v4 2/3] xfrm: set the address family before the early invalid-state drop

[Qihang]

The early drop in xfrm_input() for a state that is no longer valid runs
while family is still AF_UNSPEC, so xfrm_rcv_cb() cannot find the
afinfo and the receive callback is never invoked for such a packet.
Set the family from the state before the check so that the drop path
dispatches the callback like every other drop does.

This is also a prerequisite for releasing the tunnel device reference
on that drop path in the next patch: without a family, the release
cannot tell an ip_tunnel from an ip6_tnl.

Fixes: 4ce3dbe397d7 ("xfrm: Fix xfrm_input() to verify state is valid when (encap_type < 0)")
Cc: stable@vger.kernel.org
Signed-off-by: Qihang <q.h.hack.winter@gmail.com>
---
 net/xfrm/xfrm_input.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 94de4f698c33..517369ba9efe 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -487,6 +487,7 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 				      encap_type == UDP_ENCAP_ESPINUDP))) {
 		x = xfrm_input_state(skb);
 		xfrm_proto = x->type ? x->type->proto : nexthdr;
+		family = x->props.family;
 
 		if (unlikely(x->km.state != XFRM_STATE_VALID)) {
 			if (x->km.state == XFRM_STATE_ACQ)
@@ -500,8 +501,6 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 			goto drop;
 		}
 
-		family = x->props.family;
-
 		/* An encap_type of -2 indicates reconstructed inner packet */
 		if (encap_type == -2)
 			goto resume_decapped;
-- 
2.54.0 (Apple Git-157)

[PATCH net v4 3/3] xfrm: hold the tunnel device reference across the input path

[Qihang]

vti_input() and vti6_input_proto() cache the tunnel pointer in the skb
control buffer without taking a reference.  With async crypto the
receive callback runs from the crypto completion, after a possible
device teardown, and dereferences the freed tunnel device:

    BUG: KASAN: slab-use-after-free in vti_rcv_cb

Take a reference on the tunnel device when the pointer is cached.  The
tunnel is the device's private area, so the reference keeps the tunnel
structure alive as well.  xfrm6_rcv_spi() takes the same reference for
the tunnel it is given; it is a separate entry point, so vti6 does not
hold the reference twice.

A successful vti/vti6 callback leaves the cached tunnel in place for
xfrm_input() to release after delivery.  A callback that fails only
updates the error counters; the common drop path releases the reference
after the skb has been freed.  The helper takes the device out of the
skb before gro_cells_receive() and transport_finish(), which may already
consume the skb.  The device reference is therefore always dropped after
the skb is gone.

IPTFS consumes the outer skb itself and frees it directly, so it must
release the reference as well.  The IPTFS state carries the address
family the tunnel was resolved for, and the caller passes it in.  Add
xfrm_input_drop() and xfrm_input_consume() for the outer-skb free paths
in __input_process_payload(), iptfs_input_ordered(), iptfs_input(),
iptfs_drop_timer() and iptfs_destroy_state().  Only the outer skb
carries the cached tunnel; the inner skbs built by iptfs_alloc_skb()
have a zeroed control buffer, so they do not release it.  The drop paths
keep their skb drop reason and the consumed skb keeps consume_skb()
semantics.

The reference is released right after gro_cells_receive(); the NAPI
that processes the queued skb later still uses skb->dev without a
reference.  That window is pre-existing and is not changed here.

This depends on the previous two patches: the receive callbacks must
run before the async dev_put(), and the early drop must know the
address family to release the reference.

Fixes: df3893c176e9 ("vti: Update the ipv4 side to use it's own receive hook.")
Fixes: fa9ad96d4905 ("vti6: Update the ipv6 side to use its own receive hook.")
Cc: stable@vger.kernel.org
Signed-off-by: Qihang <q.h.hack.winter@gmail.com>
---
 net/ipv4/ip_vti.c      |  3 ++
 net/ipv6/ip6_vti.c     |  4 +++
 net/ipv6/xfrm6_input.c |  3 ++
 net/xfrm/xfrm_inout.h  |  4 +++
 net/xfrm/xfrm_input.c  | 67 +++++++++++++++++++++++++++++++++++++++++-
 net/xfrm/xfrm_iptfs.c  | 25 ++++++++++------
 6 files changed, 96 insertions(+), 10 deletions(-)

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 3b80929994a0..cbe7906a4a1b 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -63,6 +63,9 @@ static int vti_input(struct sk_buff *skb, int nexthdr, __be32 spi,
 
 		XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip4 = tunnel;
 
+		/* Kept until xfrm_input() is done with the skb. */
+		dev_hold(tunnel->dev);
+
 		if (update_skb_dev)
 			skb->dev = tunnel->dev;
 
diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index ab94b3a4ba9c..73a65b853be0 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -319,6 +319,10 @@ static int vti6_input_proto(struct sk_buff *skb, int nexthdr, __be32 spi,
 			goto discard;
 		}
 
+		/* Keep the tunnel device alive until xfrm_input() is done
+		 * with the skb, including an async crypto resumption.
+		 */
+		dev_hold(t->dev);
 		rcu_read_unlock();
 
 		XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 = t;
diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c
index 07edef258984..d27bc24f1b16 100644
--- a/net/ipv6/xfrm6_input.c
+++ b/net/ipv6/xfrm6_input.c
@@ -15,6 +15,7 @@
 #include <linux/netfilter.h>
 #include <linux/netfilter_ipv6.h>
 #include <net/ipv6.h>
+#include <net/ip6_tunnel.h>
 #include <net/xfrm.h>
 #include <net/protocol.h>
 #include <net/gro.h>
@@ -23,6 +24,8 @@ int xfrm6_rcv_spi(struct sk_buff *skb, int nexthdr, __be32 spi,
 		  struct ip6_tnl *t)
 {
 	XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip6 = t;
+	if (t)
+		dev_hold(t->dev);
 	XFRM_SPI_SKB_CB(skb)->family = AF_INET6;
 	XFRM_SPI_SKB_CB(skb)->daddroff = offsetof(struct ipv6hdr, daddr);
 	return xfrm_input(skb, nexthdr, spi, 0);
diff --git a/net/xfrm/xfrm_inout.h b/net/xfrm/xfrm_inout.h
index efc5e6b2e87b..8bd05f62ad56 100644
--- a/net/xfrm/xfrm_inout.h
+++ b/net/xfrm/xfrm_inout.h
@@ -6,6 +6,10 @@
 #ifndef XFRM_INOUT_H
 #define XFRM_INOUT_H 1
 
+void xfrm_input_drop(struct sk_buff *skb, unsigned int family,
+		     enum skb_drop_reason reason);
+void xfrm_input_consume(struct sk_buff *skb, unsigned int family);
+
 static inline void xfrm4_extract_header(struct sk_buff *skb)
 {
 	const struct iphdr *iph = ip_hdr(skb);
diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 517369ba9efe..209fd7ffb5c8 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -120,6 +120,60 @@ static int xfrm_rcv_cb(struct sk_buff *skb, unsigned int family, u8 protocol,
 	return ret;
 }
 
+/*
+ * vti/vti6 cache the tunnel in the skb control buffer and keep a
+ * reference on its net_device.  The tunnel is the device's private
+ * area, so the reference keeps both alive.  xfrm_input() releases it
+ * once the packet has been delivered; the drop paths release it when
+ * no receive callback ran.  The caller passes the address family of the
+ * cached tunnel.
+ */
+static struct net_device *xfrm_input_take_tunnel_dev(struct sk_buff *skb,
+						     unsigned int family)
+{
+	void *slot = (void *)XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip4;
+	struct net_device *dev;
+
+	if (!slot)
+		return NULL;
+
+	switch (family) {
+	case AF_INET:
+		dev = ((struct ip_tunnel *)slot)->dev;
+		break;
+	case AF_INET6:
+		dev = ((struct ip6_tnl *)slot)->dev;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return NULL;
+	}
+
+	XFRM_TUNNEL_SKB_CB(skb)->tunnel.ip4 = NULL;
+	return dev;
+}
+
+void xfrm_input_drop(struct sk_buff *skb, unsigned int family,
+		     enum skb_drop_reason reason)
+{
+	struct net_device *dev = xfrm_input_take_tunnel_dev(skb, family);
+
+	kfree_skb_reason(skb, reason);
+	if (dev)
+		dev_put(dev);
+}
+EXPORT_SYMBOL(xfrm_input_drop);
+
+void xfrm_input_consume(struct sk_buff *skb, unsigned int family)
+{
+	struct net_device *dev = xfrm_input_take_tunnel_dev(skb, family);
+
+	consume_skb(skb);
+	if (dev)
+		dev_put(dev);
+}
+EXPORT_SYMBOL(xfrm_input_consume);
+
 struct sec_path *secpath_set(struct sk_buff *skb)
 {
 	struct sec_path *sp, *tmp = skb_ext_find(skb, SKB_EXT_SEC_PATH);
@@ -468,6 +522,7 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 	const struct xfrm_state_afinfo *afinfo;
 	struct net *net = dev_net(skb->dev);
 	struct net_device *dev = skb->dev;
+	struct net_device *tdev;
 	int err;
 	__be32 seq;
 	__be32 seq_hi;
@@ -748,7 +803,11 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 			skb_dst_drop(skb);
 		if (async)
 			dev_put(dev);
+		/* gro_cells_receive() may free the skb. */
+		tdev = xfrm_input_take_tunnel_dev(skb, family);
 		gro_cells_receive(&gro_cells, skb);
+		if (tdev)
+			dev_put(tdev);
 		rcu_read_unlock();
 		return 0;
 	} else {
@@ -756,6 +815,7 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 		if (xo)
 			xfrm_gro = xo->flags & XFRM_GRO;
 
+		tdev = xfrm_input_take_tunnel_dev(skb, family);
 		err = -EAFNOSUPPORT;
 		afinfo = xfrm_state_afinfo_get_rcu(family);
 		if (likely(afinfo))
@@ -769,6 +829,8 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 			gro_cells_receive(&gro_cells, skb);
 		}
 
+		if (tdev)
+			dev_put(tdev);
 		if (async)
 			dev_put(dev);
 		rcu_read_unlock();
@@ -779,9 +841,12 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 	spin_unlock(&x->lock);
 drop:
 	xfrm_rcv_cb(skb, family, xfrm_proto, -1);
+	tdev = xfrm_input_take_tunnel_dev(skb, family);
+	kfree_skb(skb);
+	if (tdev)
+		dev_put(tdev);
 	if (async)
 		dev_put(dev);
-	kfree_skb(skb);
 	return 0;
 }
 EXPORT_SYMBOL(xfrm_input);
diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c
index 6920940a35b4..657dce0c9fdf 100644
--- a/net/xfrm/xfrm_iptfs.c
+++ b/net/xfrm/xfrm_iptfs.c
@@ -709,8 +709,9 @@ static void __iptfs_reassem_done(struct xfrm_iptfs_data *xtfs, bool free)
 
 	/* We don't care if it works locking takes care of things */
 	hrtimer_try_to_cancel(&xtfs->drop_timer);
-	if (free)
-		kfree_skb(xtfs->ra_newskb);
+	if (free && xtfs->ra_newskb)
+		xfrm_input_drop(xtfs->ra_newskb, xtfs->x->props.family,
+				SKB_DROP_REASON_NOT_SPECIFIED);
 	xtfs->ra_newskb = NULL;
 }
 
@@ -1204,14 +1205,15 @@ static bool __input_process_payload(struct xfrm_state *x, u32 data,
 	skb_abort_seq_read(skbseq);
 
 	if (defer) {
-		consume_skb(defer);
+		xfrm_input_consume(defer, x->props.family);
 	} else if (!first_skb) {
 		/* skb is the original passed in skb, but we didn't get far
 		 * enough to process it as the first_skb, if we had it would
 		 * either be save in ra_newskb, trimmed and sent on as an skb or
 		 * placed in defer to be freed.
 		 */
-		kfree_skb(skb);
+		xfrm_input_drop(skb, x->props.family,
+				SKB_DROP_REASON_NOT_SPECIFIED);
 	}
 	return true;
 }
@@ -1298,7 +1300,8 @@ static void iptfs_input_ordered(struct xfrm_state *x, struct sk_buff *skb)
 	if (!consumed) {
 		skb = skbseq.root_skb;
 		skb_abort_seq_read(&skbseq);
-		kfree_skb(skb);
+		xfrm_input_drop(skb, x->props.family,
+				SKB_DROP_REASON_NOT_SPECIFIED);
 	}
 }
 
@@ -1700,7 +1703,8 @@ static enum hrtimer_restart iptfs_drop_timer(struct hrtimer *me)
 	spin_unlock(&xtfs->drop_lock);
 
 	if (skb)
-		kfree_skb_reason(skb, SKB_DROP_REASON_FRAG_REASM_TIMEOUT);
+		xfrm_input_drop(skb, x->props.family,
+				SKB_DROP_REASON_FRAG_REASM_TIMEOUT);
 
 	if (count) {
 		list_for_each_entry_safe(skb, next, &list, list) {
@@ -1751,7 +1755,8 @@ static int iptfs_input(struct xfrm_state *x, struct sk_buff *skb)
 
 	list_for_each_entry_safe(skb, next, &freelist, list) {
 		skb_list_del_init(skb);
-		kfree_skb(skb);
+		xfrm_input_drop(skb, x->props.family,
+				SKB_DROP_REASON_NOT_SPECIFIED);
 	}
 done:
 	/* We always have dealt with the input SKB, either we are re-using it,
@@ -2752,11 +2757,13 @@ static void iptfs_destroy_state(struct xfrm_state *x)
 	hrtimer_cancel(&xtfs->drop_timer);
 
 	if (xtfs->ra_newskb)
-		kfree_skb(xtfs->ra_newskb);
+		xfrm_input_drop(xtfs->ra_newskb, xtfs->x->props.family,
+				SKB_DROP_REASON_NOT_SPECIFIED);
 
 	for (s = xtfs->w_saved, se = s + xtfs->w_savedlen; s < se; s++) {
 		if (s->skb)
-			kfree_skb(s->skb);
+			xfrm_input_drop(s->skb, x->props.family,
+					SKB_DROP_REASON_NOT_SPECIFIED);
 	}
 
 	kfree_sensitive(xtfs->w_saved);
-- 
2.54.0 (Apple Git-157)

Re: [PATCH net v4 0/3] xfrm: fix vti tunnel device use-after-free across async crypto resumption

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.