[PATCH ipsec v2] esp: fix page frag reference leak on skb_to_sgvec failure

[Alessandro Schino]

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@xxxxxxxxx>
---
v2: split the long line in esp_ssg_unref() to keep it under 100 columns

 net/ipv4/esp4.c | 7 +++++--
 net/ipv6/esp6.c | 7 +++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 2429c7845984..dfc81ee969ae 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -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 (already_unref || req->src != req->dst)
-		for (sg = sg_next(already_unref ? esp_req_sg(aead, req) : 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
diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 50af6ab9b8fc..296b57926abb 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -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 (already_unref || req->src != req->dst)
-		for (sg = sg_next(already_unref ? esp_req_sg(aead, req) : 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
-- 
2.41.0.windows.3