[PATCH] flow: Don't crash if guest attempts to connect to port 0

[PATCH] flow: Don't crash if guest attempts to connect to port 0

[David Gibson]

Using a zero port on TCP or UDP is dubious, and we can't really deal with
forwarding such a flow within the constraints of the socket API.  Hence
we ASSERT()ed that we had non-zero ports in flow_hash().

The intention was to make sure that the protocol code sanitizes such ports
before completing a flow entry.  Unfortunately, flow_hash() is also called
on new packets to see if they have an existing flow, so the unsanitized
guest packet can crash passt with the assert.

Correct this by moving the assert from flow_hash() to flow_sidx_hash()
which is only used on entries already in the table, not on unsanitized
data.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 flow.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/flow.c b/flow.c
index 687e9fd0..93b687dc 100644
--- a/flow.c
+++ b/flow.c
@@ -561,12 +561,6 @@ static uint64_t flow_hash(const struct ctx *c, uint8_t proto, uint8_t pif,
 {
 	struct siphash_state state = SIPHASH_INIT(c->hash_secret);
 
-	/* For the hash table to work, we need complete endpoint information,
-	 * and at least a forwarding port.
-	 */
-	ASSERT(pif != PIF_NONE && !inany_is_unspecified(&side->eaddr) &&
-	       side->eport != 0 && side->fport != 0);
-
 	inany_siphash_feed(&state, &side->faddr);
 	inany_siphash_feed(&state, &side->eaddr);
 
@@ -586,8 +580,16 @@ static uint64_t flow_hash(const struct ctx *c, uint8_t proto, uint8_t pif,
 static uint64_t flow_sidx_hash(const struct ctx *c, flow_sidx_t sidx)
 {
 	const struct flow_common *f = &flow_at_sidx(sidx)->f;
-	return flow_hash(c, FLOW_PROTO(f),
-			 f->pif[sidx.sidei], &f->side[sidx.sidei]);
+	const struct flowside *side = &f->side[sidx.sidei];
+	uint8_t pif = f->pif[sidx.sidei];
+
+	/* For the hash table to work, entries must have complete endpoint
+	 * information, and at least a forwarding port.
+	 */
+	ASSERT(pif != PIF_NONE && !inany_is_unspecified(&side->eaddr) &&
+	       side->eport != 0 && side->fport != 0);
+
+	return flow_hash(c, FLOW_PROTO(f), pif, side);
 }
 
 /**
-- 
@@ -561,12 +561,6 @@ static uint64_t flow_hash(const struct ctx *c, uint8_t proto, uint8_t pif,
 {
 	struct siphash_state state = SIPHASH_INIT(c->hash_secret);
 
-	/* For the hash table to work, we need complete endpoint information,
-	 * and at least a forwarding port.
-	 */
-	ASSERT(pif != PIF_NONE && !inany_is_unspecified(&side->eaddr) &&
-	       side->eport != 0 && side->fport != 0);
-
 	inany_siphash_feed(&state, &side->faddr);
 	inany_siphash_feed(&state, &side->eaddr);
 
@@ -586,8 +580,16 @@ static uint64_t flow_hash(const struct ctx *c, uint8_t proto, uint8_t pif,
 static uint64_t flow_sidx_hash(const struct ctx *c, flow_sidx_t sidx)
 {
 	const struct flow_common *f = &flow_at_sidx(sidx)->f;
-	return flow_hash(c, FLOW_PROTO(f),
-			 f->pif[sidx.sidei], &f->side[sidx.sidei]);
+	const struct flowside *side = &f->side[sidx.sidei];
+	uint8_t pif = f->pif[sidx.sidei];
+
+	/* For the hash table to work, entries must have complete endpoint
+	 * information, and at least a forwarding port.
+	 */
+	ASSERT(pif != PIF_NONE && !inany_is_unspecified(&side->eaddr) &&
+	       side->eport != 0 && side->fport != 0);
+
+	return flow_hash(c, FLOW_PROTO(f), pif, side);
 }
 
 /**
-- 
2.46.0

Re: [PATCH] flow: Don't crash if guest attempts to connect to port 0

[Stefano Brivio]

On Wed, 14 Aug 2024 20:03:33 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> Using a zero port on TCP or UDP is dubious, and we can't really deal with
> forwarding such a flow within the constraints of the socket API.  Hence
> we ASSERT()ed that we had non-zero ports in flow_hash().
> 
> The intention was to make sure that the protocol code sanitizes such ports
> before completing a flow entry.  Unfortunately, flow_hash() is also called
> on new packets to see if they have an existing flow, so the unsanitized
> guest packet can crash passt with the assert.
> 
> Correct this by moving the assert from flow_hash() to flow_sidx_hash()
> which is only used on entries already in the table, not on unsanitized
> data.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Applied, with:

  Reported-by: Matt Hamilton <matt@thmail.io>

-- 
Stefano