[PATCH] xfrm: Duplicate SPI Handling

[PATCH] xfrm: Duplicate SPI Handling

[Aakash Kumar S]

        The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
        Netlink message, which triggers the kernel function xfrm_alloc_spi().
        This function is expected to ensure uniqueness of the Security Parameter
        Index (SPI) for inbound Security Associations (SAs). However, it can
        return success even when the requested SPI is already in use, leading
        to duplicate SPIs assigned to multiple inbound SAs, differentiated
        only by their destination addresses.

        This behavior causes inconsistencies during SPI lookups for inbound packets.
        Since the lookup may return an arbitrary SA among those with the same SPI,
        packet processing can fail, resulting in packet drops.

        According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
        is uniquely identified by the SPI and optionally protocol.

	Reproducing the Issue Reliably:
	To consistently reproduce the problem, restrict the available SPI range in
	charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
	This limits the system to only 2 usable SPI values.
	Next, create more than 2 Child SA. each using unique pair of src/dst address.
	As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
	SPI, since the SPI pool is already exhausted.
	With a narrow SPI range, the issue is consistently reproducible.
	With a broader/default range, it becomes rare and unpredictable.

        Current implementation:
        xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
        So if two SAs have the same SPI but different destination addresses, then
        they will:
           a. Hash into different buckets
           b. Be stored in different linked lists (byspi + h)
           c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
        As a result, the lookup will result in NULL and kernel allows that Duplicate SPI

        Proposed Change:
        xfrm_state_lookup_spi_proto() does a truly global search - across all states,
        regardless of hash bucket and matches SPI and proto.

        Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
---
 include/net/xfrm.h    |  3 +++
 net/xfrm/xfrm_state.c | 39 +++++++++++++++++++++++++++++++--------
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 39365fd2ea17..bd128980e8fd 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1693,6 +1693,9 @@ struct xfrm_state *xfrm_stateonly_find(struct net *net, u32 mark, u32 if_id,
 				       u8 mode, u8 proto, u32 reqid);
 struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 					      unsigned short family);
+struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi,
+						u8 proto);
+
 int xfrm_state_check_expire(struct xfrm_state *x);
 void xfrm_state_update_stats(struct net *net);
 #ifdef CONFIG_XFRM_OFFLOAD
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 341d79ecb5c2..9820025610ee 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1714,6 +1714,29 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 }
 EXPORT_SYMBOL(xfrm_state_lookup_byspi);
 
+struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
+{
+    struct xfrm_state *x;
+    unsigned int i;
+
+    rcu_read_lock();
+
+    for (i = 0; i <= net->xfrm.state_hmask; i++) {
+        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
+            if (x->id.spi == spi && x->id.proto == proto) {
+                if (!xfrm_state_hold_rcu(x))
+                    continue;
+                rcu_read_unlock();
+                return x;
+            }
+        }
+    }
+
+    rcu_read_unlock();
+    return NULL;
+}
+EXPORT_SYMBOL(xfrm_state_lookup_spi_proto);
+
 static void __xfrm_state_insert(struct xfrm_state *x)
 {
 	struct net *net = xs_net(x);
@@ -2550,7 +2573,6 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	__be32 minspi = htonl(low);
 	__be32 maxspi = htonl(high);
 	__be32 newspi = 0;
-	u32 mark = x->mark.v & x->mark.m;
 
 	spin_lock_bh(&x->lock);
 	if (x->km.state == XFRM_STATE_DEAD) {
@@ -2565,18 +2587,12 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	err = -ENOENT;
 
 	if (minspi == maxspi) {
-		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
-		if (x0) {
-			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
-			xfrm_state_put(x0);
-			goto unlock;
-		}
 		newspi = minspi;
 	} else {
 		u32 spi = 0;
 		for (h = 0; h < high-low+1; h++) {
 			spi = get_random_u32_inclusive(low, high);
-			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
+			x0 = xfrm_state_lookup_spi_proto(net, htonl(spi), x->id.proto);
 			if (x0 == NULL) {
 				newspi = htonl(spi);
 				break;
@@ -2586,6 +2602,13 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	}
 	if (newspi) {
 		spin_lock_bh(&net->xfrm.xfrm_state_lock);
+		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
+		if (x0) {
+			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
+			xfrm_state_put(x0);
+			goto unlock;
+		}
+
 		x->id.spi = newspi;
 		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
 		XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h,
-- 
2.43.0

Re: [PATCH] xfrm: Duplicate SPI Handling

[Steffen Klassert]

On Mon, Jun 16, 2025 at 03:36:21PM +0530, Aakash Kumar S wrote:
>         The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
>         Netlink message, which triggers the kernel function xfrm_alloc_spi().
>         This function is expected to ensure uniqueness of the Security Parameter
>         Index (SPI) for inbound Security Associations (SAs). However, it can
>         return success even when the requested SPI is already in use, leading
>         to duplicate SPIs assigned to multiple inbound SAs, differentiated
>         only by their destination addresses.
> 
>         This behavior causes inconsistencies during SPI lookups for inbound packets.
>         Since the lookup may return an arbitrary SA among those with the same SPI,
>         packet processing can fail, resulting in packet drops.
> 
>         According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
>         is uniquely identified by the SPI and optionally protocol.
> 
> 	Reproducing the Issue Reliably:
> 	To consistently reproduce the problem, restrict the available SPI range in
> 	charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
> 	This limits the system to only 2 usable SPI values.
> 	Next, create more than 2 Child SA. each using unique pair of src/dst address.
> 	As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
> 	SPI, since the SPI pool is already exhausted.
> 	With a narrow SPI range, the issue is consistently reproducible.
> 	With a broader/default range, it becomes rare and unpredictable.
> 
>         Current implementation:
>         xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
>         So if two SAs have the same SPI but different destination addresses, then
>         they will:
>            a. Hash into different buckets
>            b. Be stored in different linked lists (byspi + h)
>            c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
>         As a result, the lookup will result in NULL and kernel allows that Duplicate SPI
> 
>         Proposed Change:
>         xfrm_state_lookup_spi_proto() does a truly global search - across all states,
>         regardless of hash bucket and matches SPI and proto.
> 
>         Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>

Nit: Please remove the leading whitespaces from the commit message
so that I don't have to hand edit it when applying.

> ---
>  include/net/xfrm.h    |  3 +++
>  net/xfrm/xfrm_state.c | 39 +++++++++++++++++++++++++++++++--------
>  2 files changed, 34 insertions(+), 8 deletions(-)
> 
> diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> index 39365fd2ea17..bd128980e8fd 100644
> --- a/include/net/xfrm.h
> +++ b/include/net/xfrm.h
> @@ -1693,6 +1693,9 @@ struct xfrm_state *xfrm_stateonly_find(struct net *net, u32 mark, u32 if_id,
>  				       u8 mode, u8 proto, u32 reqid);
>  struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
>  					      unsigned short family);
> +struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi,
> +						u8 proto);
> +
>  int xfrm_state_check_expire(struct xfrm_state *x);
>  void xfrm_state_update_stats(struct net *net);
>  #ifdef CONFIG_XFRM_OFFLOAD
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index 341d79ecb5c2..9820025610ee 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -1714,6 +1714,29 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
>  }
>  EXPORT_SYMBOL(xfrm_state_lookup_byspi);
>  
> +struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
> +{
> +    struct xfrm_state *x;
> +    unsigned int i;
> +
> +    rcu_read_lock();
> +
> +    for (i = 0; i <= net->xfrm.state_hmask; i++) {
> +        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
> +            if (x->id.spi == spi && x->id.proto == proto) {
> +                if (!xfrm_state_hold_rcu(x))
> +                    continue;
> +                rcu_read_unlock();
> +                return x;
> +            }
> +        }
> +    }
> +
> +    rcu_read_unlock();
> +    return NULL;
> +}
> +EXPORT_SYMBOL(xfrm_state_lookup_spi_proto);

Do we really need to export this function? It is used just
in net/xfrm/xfrm_state.c

[PATCH] xfrm: Duplicate SPI Handling

[Aakash Kumar S]

The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
Netlink message, which triggers the kernel function xfrm_alloc_spi().
This function is expected to ensure uniqueness of the Security Parameter
Index (SPI) for inbound Security Associations (SAs). However, it can
return success even when the requested SPI is already in use, leading
to duplicate SPIs assigned to multiple inbound SAs, differentiated
only by their destination addresses.

This behavior causes inconsistencies during SPI lookups for inbound packets.
Since the lookup may return an arbitrary SA among those with the same SPI,
packet processing can fail, resulting in packet drops.

According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
is uniquely identified by the SPI and optionally protocol.

Reproducing the Issue Reliably:
To consistently reproduce the problem, restrict the available SPI range in
charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
This limits the system to only 2 usable SPI values.
Next, create more than 2 Child SA. each using unique pair of src/dst address.
As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
SPI, since the SPI pool is already exhausted.
With a narrow SPI range, the issue is consistently reproducible.
With a broader/default range, it becomes rare and unpredictable.

Current implementation:
xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
So if two SAs have the same SPI but different destination addresses, then
they will:
a. Hash into different buckets
b. Be stored in different linked lists (byspi + h)
c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
As a result, the lookup will result in NULL and kernel allows that Duplicate SPI

Proposed Change:
xfrm_state_lookup_spi_proto() does a truly global search - across all states,
regardless of hash bucket and matches SPI and proto.

Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
---
 include/net/xfrm.h    |  3 +++
 net/xfrm/xfrm_state.c | 38 ++++++++++++++++++++++++++++++--------
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 39365fd2ea17..bd128980e8fd 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1693,6 +1693,9 @@ struct xfrm_state *xfrm_stateonly_find(struct net *net, u32 mark, u32 if_id,
 				       u8 mode, u8 proto, u32 reqid);
 struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 					      unsigned short family);
+struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi,
+						u8 proto);
+
 int xfrm_state_check_expire(struct xfrm_state *x);
 void xfrm_state_update_stats(struct net *net);
 #ifdef CONFIG_XFRM_OFFLOAD
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 341d79ecb5c2..fb05f47898fe 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1714,6 +1714,28 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 }
 EXPORT_SYMBOL(xfrm_state_lookup_byspi);
 
+struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
+{
+    struct xfrm_state *x;
+    unsigned int i;
+
+    rcu_read_lock();
+
+    for (i = 0; i <= net->xfrm.state_hmask; i++) {
+        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
+            if (x->id.spi == spi && x->id.proto == proto) {
+                if (!xfrm_state_hold_rcu(x))
+                    continue;
+                rcu_read_unlock();
+                return x;
+            }
+        }
+    }
+
+    rcu_read_unlock();
+    return NULL;
+}
+
 static void __xfrm_state_insert(struct xfrm_state *x)
 {
 	struct net *net = xs_net(x);
@@ -2550,7 +2572,6 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	__be32 minspi = htonl(low);
 	__be32 maxspi = htonl(high);
 	__be32 newspi = 0;
-	u32 mark = x->mark.v & x->mark.m;
 
 	spin_lock_bh(&x->lock);
 	if (x->km.state == XFRM_STATE_DEAD) {
@@ -2565,18 +2586,12 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	err = -ENOENT;
 
 	if (minspi == maxspi) {
-		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
-		if (x0) {
-			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
-			xfrm_state_put(x0);
-			goto unlock;
-		}
 		newspi = minspi;
 	} else {
 		u32 spi = 0;
 		for (h = 0; h < high-low+1; h++) {
 			spi = get_random_u32_inclusive(low, high);
-			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
+			x0 = xfrm_state_lookup_spi_proto(net, htonl(spi), x->id.proto);
 			if (x0 == NULL) {
 				newspi = htonl(spi);
 				break;
@@ -2586,6 +2601,13 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	}
 	if (newspi) {
 		spin_lock_bh(&net->xfrm.xfrm_state_lock);
+		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
+		if (x0) {
+			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
+			xfrm_state_put(x0);
+			goto unlock;
+		}
+
 		x->id.spi = newspi;
 		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
 		XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h,
-- 
2.43.0

Re: [PATCH] xfrm: Duplicate SPI Handling

[Steffen Klassert]

On Fri, Jun 20, 2025 at 03:08:23PM +0530, Aakash Kumar S wrote:
> The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
> Netlink message, which triggers the kernel function xfrm_alloc_spi().
> This function is expected to ensure uniqueness of the Security Parameter
> Index (SPI) for inbound Security Associations (SAs). However, it can
> return success even when the requested SPI is already in use, leading
> to duplicate SPIs assigned to multiple inbound SAs, differentiated
> only by their destination addresses.
> 
> This behavior causes inconsistencies during SPI lookups for inbound packets.
> Since the lookup may return an arbitrary SA among those with the same SPI,
> packet processing can fail, resulting in packet drops.
> 
> According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
> is uniquely identified by the SPI and optionally protocol.
> 
> Reproducing the Issue Reliably:
> To consistently reproduce the problem, restrict the available SPI range in
> charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
> This limits the system to only 2 usable SPI values.
> Next, create more than 2 Child SA. each using unique pair of src/dst address.
> As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
> SPI, since the SPI pool is already exhausted.
> With a narrow SPI range, the issue is consistently reproducible.
> With a broader/default range, it becomes rare and unpredictable.
> 
> Current implementation:
> xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
> So if two SAs have the same SPI but different destination addresses, then
> they will:
> a. Hash into different buckets
> b. Be stored in different linked lists (byspi + h)
> c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
> As a result, the lookup will result in NULL and kernel allows that Duplicate SPI
> 
> Proposed Change:
> xfrm_state_lookup_spi_proto() does a truly global search - across all states,
> regardless of hash bucket and matches SPI and proto.
> 
> Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
> ---
>  include/net/xfrm.h    |  3 +++
>  net/xfrm/xfrm_state.c | 38 ++++++++++++++++++++++++++++++--------
>  2 files changed, 33 insertions(+), 8 deletions(-)
> 
> diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> index 39365fd2ea17..bd128980e8fd 100644
> --- a/include/net/xfrm.h
> +++ b/include/net/xfrm.h
> @@ -1693,6 +1693,9 @@ struct xfrm_state *xfrm_stateonly_find(struct net *net, u32 mark, u32 if_id,
>  				       u8 mode, u8 proto, u32 reqid);
>  struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
>  					      unsigned short family);
> +struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi,
> +						u8 proto);
> +
>  int xfrm_state_check_expire(struct xfrm_state *x);
>  void xfrm_state_update_stats(struct net *net);
>  #ifdef CONFIG_XFRM_OFFLOAD
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index 341d79ecb5c2..fb05f47898fe 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -1714,6 +1714,28 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
>  }
>  EXPORT_SYMBOL(xfrm_state_lookup_byspi);
>  
> +struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
> +{
> +    struct xfrm_state *x;
> +    unsigned int i;
> +
> +    rcu_read_lock();
> +
> +    for (i = 0; i <= net->xfrm.state_hmask; i++) {
> +        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
> +            if (x->id.spi == spi && x->id.proto == proto) {
> +                if (!xfrm_state_hold_rcu(x))
> +                    continue;
> +                rcu_read_unlock();
> +                return x;
> +            }
> +        }
> +    }
> +
> +    rcu_read_unlock();
> +    return NULL;
> +}

Now, that the function is not exported anymore, it can be static.

[PATCH] xfrm: Duplicate SPI Handling

[Aakash Kumar S]

The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
Netlink message, which triggers the kernel function xfrm_alloc_spi().
This function is expected to ensure uniqueness of the Security Parameter
Index (SPI) for inbound Security Associations (SAs). However, it can
return success even when the requested SPI is already in use, leading
to duplicate SPIs assigned to multiple inbound SAs, differentiated
only by their destination addresses.

This behavior causes inconsistencies during SPI lookups for inbound packets.
Since the lookup may return an arbitrary SA among those with the same SPI,
packet processing can fail, resulting in packet drops.

According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
is uniquely identified by the SPI and optionally protocol.

Reproducing the Issue Reliably:
To consistently reproduce the problem, restrict the available SPI range in
charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
This limits the system to only 2 usable SPI values.
Next, create more than 2 Child SA. each using unique pair of src/dst address.
As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
SPI, since the SPI pool is already exhausted.
With a narrow SPI range, the issue is consistently reproducible.
With a broader/default range, it becomes rare and unpredictable.

Current implementation:
xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
So if two SAs have the same SPI but different destination addresses, then
they will:
a. Hash into different buckets
b. Be stored in different linked lists (byspi + h)
c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
As a result, the lookup will result in NULL and kernel allows that Duplicate SPI

Proposed Change:
xfrm_state_lookup_spi_proto() does a truly global search - across all states,
regardless of hash bucket and matches SPI and proto.

Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
---
 net/xfrm/xfrm_state.c | 38 ++++++++++++++++++++++++++++++--------
 1 file changed, 30 insertions(+), 8 deletions(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 341d79ecb5c2..6e6bc1818903 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1714,6 +1714,28 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 }
 EXPORT_SYMBOL(xfrm_state_lookup_byspi);
 
+static struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
+{
+    struct xfrm_state *x;
+    unsigned int i;
+
+    rcu_read_lock();
+
+    for (i = 0; i <= net->xfrm.state_hmask; i++) {
+        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
+            if (x->id.spi == spi && x->id.proto == proto) {
+                if (!xfrm_state_hold_rcu(x))
+                    continue;
+                rcu_read_unlock();
+                return x;
+            }
+        }
+    }
+
+    rcu_read_unlock();
+    return NULL;
+}
+
 static void __xfrm_state_insert(struct xfrm_state *x)
 {
 	struct net *net = xs_net(x);
@@ -2550,7 +2572,6 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	__be32 minspi = htonl(low);
 	__be32 maxspi = htonl(high);
 	__be32 newspi = 0;
-	u32 mark = x->mark.v & x->mark.m;
 
 	spin_lock_bh(&x->lock);
 	if (x->km.state == XFRM_STATE_DEAD) {
@@ -2565,18 +2586,12 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	err = -ENOENT;
 
 	if (minspi == maxspi) {
-		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
-		if (x0) {
-			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
-			xfrm_state_put(x0);
-			goto unlock;
-		}
 		newspi = minspi;
 	} else {
 		u32 spi = 0;
 		for (h = 0; h < high-low+1; h++) {
 			spi = get_random_u32_inclusive(low, high);
-			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
+			x0 = xfrm_state_lookup_spi_proto(net, htonl(spi), x->id.proto);
 			if (x0 == NULL) {
 				newspi = htonl(spi);
 				break;
@@ -2586,6 +2601,13 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	}
 	if (newspi) {
 		spin_lock_bh(&net->xfrm.xfrm_state_lock);
+		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
+		if (x0) {
+			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
+			xfrm_state_put(x0);
+			goto unlock;
+		}
+
 		x->id.spi = newspi;
 		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
 		XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h,
-- 
2.43.0

Re: [PATCH] xfrm: Duplicate SPI Handling

[Herbert Xu]

On Tue, Jun 24, 2025 at 03:45:16PM +0530, Aakash Kumar S wrote:
>
> @@ -2565,18 +2586,12 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
>  	err = -ENOENT;
>  
>  	if (minspi == maxspi) {
> -		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
> -		if (x0) {
> -			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
> -			xfrm_state_put(x0);
> -			goto unlock;
> -		}
>  		newspi = minspi;
>  	} else {
>  		u32 spi = 0;
>  		for (h = 0; h < high-low+1; h++) {
>  			spi = get_random_u32_inclusive(low, high);
> -			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
> +			x0 = xfrm_state_lookup_spi_proto(net, htonl(spi), x->id.proto);
>  			if (x0 == NULL) {
>  				newspi = htonl(spi);
>  				break;
> @@ -2586,6 +2601,13 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
>  	}
>  	if (newspi) {
>  		spin_lock_bh(&net->xfrm.xfrm_state_lock);
> +		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
> +		if (x0) {
> +			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
> +			xfrm_state_put(x0);
> +			goto unlock;
> +		}
> +

There is a quality of implementation problem here.  The double checks
are racy and may result in an "already in use" error even though the
specified SPI range is not fully used up.

Ideally the range check should be conducted under lock, or there should
be a retry if the insertion failed for an SPI range request.  I think
a retry would be the easiest with an additional check for signals
interrupting the request.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

[PATCH] xfrm: Duplicate SPI Handling

[Aakash Kumar S]

The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
Netlink message, which triggers the kernel function xfrm_alloc_spi().
This function is expected to ensure uniqueness of the Security Parameter
Index (SPI) for inbound Security Associations (SAs). However, it can
return success even when the requested SPI is already in use, leading
to duplicate SPIs assigned to multiple inbound SAs, differentiated
only by their destination addresses.

This behavior causes inconsistencies during SPI lookups for inbound packets.
Since the lookup may return an arbitrary SA among those with the same SPI,
packet processing can fail, resulting in packet drops.

According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
is uniquely identified by the SPI and optionally protocol.

Reproducing the Issue Reliably:
To consistently reproduce the problem, restrict the available SPI range in
charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
This limits the system to only 2 usable SPI values.
Next, create more than 2 Child SA. each using unique pair of src/dst address.
As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
SPI, since the SPI pool is already exhausted.
With a narrow SPI range, the issue is consistently reproducible.
With a broader/default range, it becomes rare and unpredictable.

Current implementation:
xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
So if two SAs have the same SPI but different destination addresses, then
they will:
a. Hash into different buckets
b. Be stored in different linked lists (byspi + h)
c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
As a result, the lookup will result in NULL and kernel allows that Duplicate SPI

Proposed Change:
xfrm_state_lookup_spi_proto() does a truly global search - across all states,
regardless of hash bucket and matches SPI and proto.

Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
---
 net/xfrm/xfrm_state.c | 78 ++++++++++++++++++++++++++-----------------
 1 file changed, 47 insertions(+), 31 deletions(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 341d79ecb5c2..74855af27d15 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1714,6 +1714,28 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 }
 EXPORT_SYMBOL(xfrm_state_lookup_byspi);
 
+static struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
+{
+    struct xfrm_state *x;
+    unsigned int i;
+
+    rcu_read_lock();
+
+    for (i = 0; i <= net->xfrm.state_hmask; i++) {
+        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
+            if (x->id.spi == spi && x->id.proto == proto) {
+                if (!xfrm_state_hold_rcu(x))
+                    continue;
+                rcu_read_unlock();
+                return x;
+            }
+        }
+    }
+
+    rcu_read_unlock();
+    return NULL;
+}
+
 static void __xfrm_state_insert(struct xfrm_state *x)
 {
 	struct net *net = xs_net(x);
@@ -2547,10 +2569,8 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	unsigned int h;
 	struct xfrm_state *x0;
 	int err = -ENOENT;
-	__be32 minspi = htonl(low);
-	__be32 maxspi = htonl(high);
+	u32 range = high - low + 1;
 	__be32 newspi = 0;
-	u32 mark = x->mark.v & x->mark.m;
 
 	spin_lock_bh(&x->lock);
 	if (x->km.state == XFRM_STATE_DEAD) {
@@ -2564,39 +2584,35 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 
 	err = -ENOENT;
 
-	if (minspi == maxspi) {
-		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
-		if (x0) {
-			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
-			xfrm_state_put(x0);
-			goto unlock;
-		}
-		newspi = minspi;
-	} else {
-		u32 spi = 0;
-		for (h = 0; h < high-low+1; h++) {
-			spi = get_random_u32_inclusive(low, high);
-			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
-			if (x0 == NULL) {
-				newspi = htonl(spi);
-				break;
-			}
-			xfrm_state_put(x0);
-		}
-	}
-	if (newspi) {
+	for (h = 0; h < range; h++) {
+		u32 spi = (low == high) ? low : get_random_u32_inclusive(low, high);
+		newspi = htonl(spi);
+
 		spin_lock_bh(&net->xfrm.xfrm_state_lock);
-		x->id.spi = newspi;
-		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
-		XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h,
-				  x->xso.type);
+		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
+		if (!x0) {
+			x->id.spi = newspi;
+			h = xfrm_spi_hash(net, &x->id.daddr, newspi, x->id.proto, x->props.family);
+			XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h, x->xso.type);
+			spin_unlock_bh(&net->xfrm.xfrm_state_lock);
+			err = 0;
+			goto unlock;
+                }
+		xfrm_state_put(x0);
 		spin_unlock_bh(&net->xfrm.xfrm_state_lock);
 
-		err = 0;
-	} else {
-		NL_SET_ERR_MSG(extack, "No SPI available in the requested range");
+		if (signal_pending(current)) {
+			err = -ERESTARTSYS;
+			goto unlock;
+                }
+
+		if (low == high)
+			break;
 	}
 
+	if (err)
+		NL_SET_ERR_MSG(extack, "No SPI available in the requested range");
+
 unlock:
 	spin_unlock_bh(&x->lock);
 
-- 
2.43.0

Re: [PATCH] xfrm: Duplicate SPI Handling

[Herbert Xu]

On Tue, Jun 24, 2025 at 11:40:54PM +0530, Aakash Kumar S wrote:
> The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
> Netlink message, which triggers the kernel function xfrm_alloc_spi().
> This function is expected to ensure uniqueness of the Security Parameter
> Index (SPI) for inbound Security Associations (SAs). However, it can
> return success even when the requested SPI is already in use, leading
> to duplicate SPIs assigned to multiple inbound SAs, differentiated
> only by their destination addresses.
> 
> This behavior causes inconsistencies during SPI lookups for inbound packets.
> Since the lookup may return an arbitrary SA among those with the same SPI,
> packet processing can fail, resulting in packet drops.
> 
> According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
> is uniquely identified by the SPI and optionally protocol.
> 
> Reproducing the Issue Reliably:
> To consistently reproduce the problem, restrict the available SPI range in
> charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
> This limits the system to only 2 usable SPI values.
> Next, create more than 2 Child SA. each using unique pair of src/dst address.
> As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
> SPI, since the SPI pool is already exhausted.
> With a narrow SPI range, the issue is consistently reproducible.
> With a broader/default range, it becomes rare and unpredictable.
> 
> Current implementation:
> xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
> So if two SAs have the same SPI but different destination addresses, then
> they will:
> a. Hash into different buckets
> b. Be stored in different linked lists (byspi + h)
> c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
> As a result, the lookup will result in NULL and kernel allows that Duplicate SPI
> 
> Proposed Change:
> xfrm_state_lookup_spi_proto() does a truly global search - across all states,
> regardless of hash bucket and matches SPI and proto.
> 
> Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
> ---
>  net/xfrm/xfrm_state.c | 78 ++++++++++++++++++++++++++-----------------
>  1 file changed, 47 insertions(+), 31 deletions(-)

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH] xfrm: Duplicate SPI Handling

[Nicolas Dichtel]

Le 24/06/2025 à 20:10, Aakash Kumar S a écrit :
> The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
> Netlink message, which triggers the kernel function xfrm_alloc_spi().
> This function is expected to ensure uniqueness of the Security Parameter
> Index (SPI) for inbound Security Associations (SAs). However, it can
> return success even when the requested SPI is already in use, leading
> to duplicate SPIs assigned to multiple inbound SAs, differentiated
> only by their destination addresses.
> 
> This behavior causes inconsistencies during SPI lookups for inbound packets.
> Since the lookup may return an arbitrary SA among those with the same SPI,
> packet processing can fail, resulting in packet drops.
> 
> According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
> is uniquely identified by the SPI and optionally protocol.
> 
> Reproducing the Issue Reliably:
> To consistently reproduce the problem, restrict the available SPI range in
> charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
> This limits the system to only 2 usable SPI values.
> Next, create more than 2 Child SA. each using unique pair of src/dst address.
> As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
> SPI, since the SPI pool is already exhausted.
> With a narrow SPI range, the issue is consistently reproducible.
> With a broader/default range, it becomes rare and unpredictable.
> 
> Current implementation:
> xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
> So if two SAs have the same SPI but different destination addresses, then
> they will:
> a. Hash into different buckets
> b. Be stored in different linked lists (byspi + h)
> c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
> As a result, the lookup will result in NULL and kernel allows that Duplicate SPI
> 
> Proposed Change:
> xfrm_state_lookup_spi_proto() does a truly global search - across all states,
> regardless of hash bucket and matches SPI and proto.
> 
> Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
> ---
>  net/xfrm/xfrm_state.c | 78 ++++++++++++++++++++++++++-----------------
>  1 file changed, 47 insertions(+), 31 deletions(-)
> 
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index 341d79ecb5c2..74855af27d15 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -1714,6 +1714,28 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
>  }
>  EXPORT_SYMBOL(xfrm_state_lookup_byspi);
>  
> +static struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
> +{
> +    struct xfrm_state *x;
> +    unsigned int i;
> +
> +    rcu_read_lock();
> +
> +    for (i = 0; i <= net->xfrm.state_hmask; i++) {
> +        hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
> +            if (x->id.spi == spi && x->id.proto == proto) {
> +                if (!xfrm_state_hold_rcu(x))
> +                    continue;
> +                rcu_read_unlock();
> +                return x;
> +            }
> +        }
> +    }
> +
> +    rcu_read_unlock();
> +    return NULL;
> +}
The whole function is indented with spaces.

> +
>  static void __xfrm_state_insert(struct xfrm_state *x)
>  {
>  	struct net *net = xs_net(x);
> @@ -2547,10 +2569,8 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
>  	unsigned int h;
>  	struct xfrm_state *x0;
>  	int err = -ENOENT;
> -	__be32 minspi = htonl(low);
> -	__be32 maxspi = htonl(high);
> +	u32 range = high - low + 1;
>  	__be32 newspi = 0;
> -	u32 mark = x->mark.v & x->mark.m;
>  
>  	spin_lock_bh(&x->lock);
>  	if (x->km.state == XFRM_STATE_DEAD) {
> @@ -2564,39 +2584,35 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
>  
>  	err = -ENOENT;
>  
> -	if (minspi == maxspi) {
> -		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
> -		if (x0) {
> -			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
> -			xfrm_state_put(x0);
> -			goto unlock;
> -		}
> -		newspi = minspi;
> -	} else {
> -		u32 spi = 0;
> -		for (h = 0; h < high-low+1; h++) {
> -			spi = get_random_u32_inclusive(low, high);
> -			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
> -			if (x0 == NULL) {
> -				newspi = htonl(spi);
> -				break;
> -			}
> -			xfrm_state_put(x0);
> -		}
> -	}
> -	if (newspi) {
> +	for (h = 0; h < range; h++) {
> +		u32 spi = (low == high) ? low : get_random_u32_inclusive(low, high);
> +		newspi = htonl(spi);
> +
>  		spin_lock_bh(&net->xfrm.xfrm_state_lock);
> -		x->id.spi = newspi;
> -		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
> -		XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h,
> -				  x->xso.type);
> +		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
> +		if (!x0) {
> +			x->id.spi = newspi;
> +			h = xfrm_spi_hash(net, &x->id.daddr, newspi, x->id.proto, x->props.family);
> +			XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h, x->xso.type);
> +			spin_unlock_bh(&net->xfrm.xfrm_state_lock);
> +			err = 0;
> +			goto unlock;
> +                }
The above line also.

> +		xfrm_state_put(x0);
>  		spin_unlock_bh(&net->xfrm.xfrm_state_lock);
>  
> -		err = 0;
> -	} else {
> -		NL_SET_ERR_MSG(extack, "No SPI available in the requested range");
> +		if (signal_pending(current)) {
> +			err = -ERESTARTSYS;
> +			goto unlock;
> +                }
And this one ^

> +
> +		if (low == high)
> +			break;
>  	}
>  
> +	if (err)
> +		NL_SET_ERR_MSG(extack, "No SPI available in the requested range");
> +
>  unlock:
>  	spin_unlock_bh(&x->lock);
>  

[PATCH] xfrm: Duplicate SPI Handling

[Aakash Kumar S]

The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
Netlink message, which triggers the kernel function xfrm_alloc_spi().
This function is expected to ensure uniqueness of the Security Parameter
Index (SPI) for inbound Security Associations (SAs). However, it can
return success even when the requested SPI is already in use, leading
to duplicate SPIs assigned to multiple inbound SAs, differentiated
only by their destination addresses.

This behavior causes inconsistencies during SPI lookups for inbound packets.
Since the lookup may return an arbitrary SA among those with the same SPI,
packet processing can fail, resulting in packet drops.

According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
is uniquely identified by the SPI and optionally protocol.

Reproducing the Issue Reliably:
To consistently reproduce the problem, restrict the available SPI range in
charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
This limits the system to only 2 usable SPI values.
Next, create more than 2 Child SA. each using unique pair of src/dst address.
As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
SPI, since the SPI pool is already exhausted.
With a narrow SPI range, the issue is consistently reproducible.
With a broader/default range, it becomes rare and unpredictable.

Current implementation:
xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
So if two SAs have the same SPI but different destination addresses, then
they will:
a. Hash into different buckets
b. Be stored in different linked lists (byspi + h)
c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
As a result, the lookup will result in NULL and kernel allows that Duplicate SPI

Proposed Change:
xfrm_state_lookup_spi_proto() does a truly global search - across all states,
regardless of hash bucket and matches SPI and proto.

Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>
---
 net/xfrm/xfrm_state.c | 72 ++++++++++++++++++++++++++-----------------
 1 file changed, 43 insertions(+), 29 deletions(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 341d79ecb5c2..0b8168a30c2e 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1714,6 +1714,26 @@ struct xfrm_state *xfrm_state_lookup_byspi(struct net *net, __be32 spi,
 }
 EXPORT_SYMBOL(xfrm_state_lookup_byspi);
 
+static struct xfrm_state *xfrm_state_lookup_spi_proto(struct net *net, __be32 spi, u8 proto)
+{
+	struct xfrm_state *x;
+	unsigned int i;
+
+	rcu_read_lock();
+	for (i = 0; i <= net->xfrm.state_hmask; i++) {
+		hlist_for_each_entry_rcu(x, &net->xfrm.state_byspi[i], byspi) {
+			if (x->id.spi == spi && x->id.proto == proto) {
+				if (!xfrm_state_hold_rcu(x))
+					continue;
+				rcu_read_unlock();
+				return x;
+			}
+		}
+	}
+	rcu_read_unlock();
+	return NULL;
+}
+
 static void __xfrm_state_insert(struct xfrm_state *x)
 {
 	struct net *net = xs_net(x);
@@ -2547,10 +2567,8 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 	unsigned int h;
 	struct xfrm_state *x0;
 	int err = -ENOENT;
-	__be32 minspi = htonl(low);
-	__be32 maxspi = htonl(high);
+	u32 range = high - low + 1;
 	__be32 newspi = 0;
-	u32 mark = x->mark.v & x->mark.m;
 
 	spin_lock_bh(&x->lock);
 	if (x->km.state == XFRM_STATE_DEAD) {
@@ -2564,38 +2582,34 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32 high,
 
 	err = -ENOENT;
 
-	if (minspi == maxspi) {
-		x0 = xfrm_state_lookup(net, mark, &x->id.daddr, minspi, x->id.proto, x->props.family);
-		if (x0) {
-			NL_SET_ERR_MSG(extack, "Requested SPI is already in use");
-			xfrm_state_put(x0);
+	for (h = 0; h < range; h++) {
+		u32 spi = (low == high) ? low : get_random_u32_inclusive(low, high);
+		newspi = htonl(spi);
+
+		spin_lock_bh(&net->xfrm.xfrm_state_lock);
+		x0 = xfrm_state_lookup_spi_proto(net, newspi, x->id.proto);
+		if (!x0) {
+			x->id.spi = newspi;
+			h = xfrm_spi_hash(net, &x->id.daddr, newspi, x->id.proto, x->props.family);
+			XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h, x->xso.type);
+			spin_unlock_bh(&net->xfrm.xfrm_state_lock);
+			err = 0;
 			goto unlock;
 		}
-		newspi = minspi;
-	} else {
-		u32 spi = 0;
-		for (h = 0; h < high-low+1; h++) {
-			spi = get_random_u32_inclusive(low, high);
-			x0 = xfrm_state_lookup(net, mark, &x->id.daddr, htonl(spi), x->id.proto, x->props.family);
-			if (x0 == NULL) {
-				newspi = htonl(spi);
-				break;
-			}
-			xfrm_state_put(x0);
+		xfrm_state_put(x0);
+		spin_unlock_bh(&net->xfrm.xfrm_state_lock);
+
+		if (signal_pending(current)) {
+			err = -ERESTARTSYS;
+			goto unlock;
 		}
+
+		if (low == high)
+			break;
 	}
-	if (newspi) {
-		spin_lock_bh(&net->xfrm.xfrm_state_lock);
-		x->id.spi = newspi;
-		h = xfrm_spi_hash(net, &x->id.daddr, x->id.spi, x->id.proto, x->props.family);
-		XFRM_STATE_INSERT(byspi, &x->byspi, net->xfrm.state_byspi + h,
-				  x->xso.type);
-		spin_unlock_bh(&net->xfrm.xfrm_state_lock);
 
-		err = 0;
-	} else {
+	if (err)
 		NL_SET_ERR_MSG(extack, "No SPI available in the requested range");
-	}
 
 unlock:
 	spin_unlock_bh(&x->lock);
-- 
2.43.0

Re: [PATCH] xfrm: Duplicate SPI Handling

[Steffen Klassert]

On Mon, Jun 30, 2025 at 06:08:56PM +0530, Aakash Kumar S wrote:
> The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
> Netlink message, which triggers the kernel function xfrm_alloc_spi().
> This function is expected to ensure uniqueness of the Security Parameter
> Index (SPI) for inbound Security Associations (SAs). However, it can
> return success even when the requested SPI is already in use, leading
> to duplicate SPIs assigned to multiple inbound SAs, differentiated
> only by their destination addresses.
> 
> This behavior causes inconsistencies during SPI lookups for inbound packets.
> Since the lookup may return an arbitrary SA among those with the same SPI,
> packet processing can fail, resulting in packet drops.
> 
> According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
> is uniquely identified by the SPI and optionally protocol.
> 
> Reproducing the Issue Reliably:
> To consistently reproduce the problem, restrict the available SPI range in
> charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
> This limits the system to only 2 usable SPI values.
> Next, create more than 2 Child SA. each using unique pair of src/dst address.
> As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
> SPI, since the SPI pool is already exhausted.
> With a narrow SPI range, the issue is consistently reproducible.
> With a broader/default range, it becomes rare and unpredictable.
> 
> Current implementation:
> xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
> So if two SAs have the same SPI but different destination addresses, then
> they will:
> a. Hash into different buckets
> b. Be stored in different linked lists (byspi + h)
> c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
> As a result, the lookup will result in NULL and kernel allows that Duplicate SPI
> 
> Proposed Change:
> xfrm_state_lookup_spi_proto() does a truly global search - across all states,
> regardless of hash bucket and matches SPI and proto.
> 
> Signed-off-by: Aakash Kumar S <saakashkumar@marvell.com>

Applied, thanks Aakash!