[PATCH 6/6] esp: fix page frag reference leak on skb_to_sgvec failure

[Steffen Klassert <steffen.klassert@secunet.com>]

From: Alessandro Schino <7991aleschino@gmail.com>

In esp_output_tail(), when esp->inplace is false, the old skb page frags
are replaced with a new page from the xfrm page_frag cache The source
scatterlist (sg) is built from the old frags before the replacement, and
esp_ssg_unref() is responsible for releasing the old page references
after the crypto operation completes

However, if the second skb_to_sgvec() call (which builds the destination
scatterlist from the new page) fails, the code jumps to error_free which
only calls kfree(tmp). The old page frag references captured in the
source scatterlist are never released:

  1 sg[] is built from old frags via skb_to_sgvec() (no extra get_page)
  2 nr_frags is set to 1 and frag[0] is replaced with the new page
  3 Second skb_to_sgvec() fails -> goto error_free

Fix this by adding a bool parameter to esp_ssg_unref() that, when true,
unconditionally unrefs the source scatterlist frags. Since req->src is
not yet initialized by aead_request_set_crypt() at the point of the
error, the source scatterlist is obtained directly via esp_req_sg()
Existing callers pass false to preserve the original behavior

The same issue exists in both esp4 and esp6 as the code is identical

Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible")
Signed-off-by: Alessandro Schino <7991aleschino@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv4/esp4.c | 17 +++++++++++------
 net/ipv6/esp6.c | 17 +++++++++++------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 513c8215c947..dfc81ee969ae 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -96,7 +96,7 @@ static inline struct scatterlist *esp_req_sg(struct crypto_aead *aead,
 			     __alignof__(struct scatterlist));
 }
 
-static void esp_ssg_unref(struct xfrm_state *x, void *tmp, struct sk_buff *skb)
+static void esp_ssg_unref(struct xfrm_state *x, void *tmp, struct sk_buff *skb, bool already_unref)
 {
 	struct crypto_aead *aead = x->data;
 	int extralen = 0;
@@ -113,10 +113,13 @@ static void esp_ssg_unref(struct xfrm_state *x, void *tmp, struct sk_buff *skb)
 	/* Unref skb_frag_pages in the src scatterlist if necessary.
 	 * Skip the first sg which comes from skb->data.
 	 */
-	if (req->src != req->dst)
-		for (sg = sg_next(req->src); sg; sg = sg_next(sg))
+	if (already_unref || req->src != req->dst) {
+		struct scatterlist *src = already_unref ? esp_req_sg(aead, req) : req->src;
+
+		for (sg = sg_next(src); sg; sg = sg_next(sg))
 			skb_page_unref(page_to_netmem(sg_page(sg)),
 				       skb->pp_recycle);
+	}
 }
 
 #ifdef CONFIG_INET_ESPINTCP
@@ -220,7 +223,7 @@ static void esp_output_done(void *data, int err)
 	}
 
 	tmp = ESP_SKB_CB(skb)->tmp;
-	esp_ssg_unref(x, tmp, skb);
+	esp_ssg_unref(x, tmp, skb, false);
 	kfree(tmp);
 
 	if (xo && (xo->flags & XFRM_DEV_RESUME)) {
@@ -569,8 +572,10 @@ int esp_output_tail(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
 		err = skb_to_sgvec(skb, dsg,
 			           (unsigned char *)esph - skb->data,
 			           assoclen + ivlen + esp->clen + alen);
-		if (unlikely(err < 0))
+		if (unlikely(err < 0)) {
+			esp_ssg_unref(x, tmp, skb, true);
 			goto error_free;
+		}
 	}
 
 	if ((x->props.flags & XFRM_STATE_ESN))
@@ -602,7 +607,7 @@ int esp_output_tail(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
 	}
 
 	if (sg != dsg)
-		esp_ssg_unref(x, tmp, skb);
+		esp_ssg_unref(x, tmp, skb, false);
 
 	if (!err && x->encap && x->encap->encap_type == TCP_ENCAP_ESPINTCP)
 		err = esp_output_tail_tcp(x, skb);
diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 57481e423e59..296b57926abb 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -113,7 +113,7 @@ static inline struct scatterlist *esp_req_sg(struct crypto_aead *aead,
 			     __alignof__(struct scatterlist));
 }
 
-static void esp_ssg_unref(struct xfrm_state *x, void *tmp, struct sk_buff *skb)
+static void esp_ssg_unref(struct xfrm_state *x, void *tmp, struct sk_buff *skb, bool already_unref)
 {
 	struct crypto_aead *aead = x->data;
 	int extralen = 0;
@@ -130,10 +130,13 @@ static void esp_ssg_unref(struct xfrm_state *x, void *tmp, struct sk_buff *skb)
 	/* Unref skb_frag_pages in the src scatterlist if necessary.
 	 * Skip the first sg which comes from skb->data.
 	 */
-	if (req->src != req->dst)
-		for (sg = sg_next(req->src); sg; sg = sg_next(sg))
+	if (already_unref || req->src != req->dst) {
+		struct scatterlist *src = already_unref ? esp_req_sg(aead, req) : req->src;
+
+		for (sg = sg_next(src); sg; sg = sg_next(sg))
 			skb_page_unref(page_to_netmem(sg_page(sg)),
 				       skb->pp_recycle);
+	}
 }
 
 #ifdef CONFIG_INET6_ESPINTCP
@@ -254,7 +257,7 @@ static void esp_output_done(void *data, int err)
 	}
 
 	tmp = ESP_SKB_CB(skb)->tmp;
-	esp_ssg_unref(x, tmp, skb);
+	esp_ssg_unref(x, tmp, skb, false);
 	kfree(tmp);
 
 	esp_output_encap_csum(skb);
@@ -600,8 +603,10 @@ int esp6_output_tail(struct xfrm_state *x, struct sk_buff *skb, struct esp_info
 		err = skb_to_sgvec(skb, dsg,
 			           (unsigned char *)esph - skb->data,
 			           assoclen + ivlen + esp->clen + alen);
-		if (unlikely(err < 0))
+		if (unlikely(err < 0)) {
+			esp_ssg_unref(x, tmp, skb, true);
 			goto error_free;
+		}
 	}
 
 	if ((x->props.flags & XFRM_STATE_ESN))
@@ -634,7 +639,7 @@ int esp6_output_tail(struct xfrm_state *x, struct sk_buff *skb, struct esp_info
 	}
 
 	if (sg != dsg)
-		esp_ssg_unref(x, tmp, skb);
+		esp_ssg_unref(x, tmp, skb, false);
 
 	if (!err && x->encap && x->encap->encap_type == TCP_ENCAP_ESPINTCP)
 		err = esp_output_tail_tcp(x, skb);
-- 
2.43.0