[PATCH ipsec] esp: Force skb_cow_data() on RX when the skb is non-linear

[Hyunwoo Kim <imv4bel@gmail.com>]

esp_input() and esp6_input() skip skb_cow_data() on uncloned skbs
through two arms: one for fully linear skbs (nfrags = 1) and one for
skbs carrying paged fragments without a frag_list, which sets
nfrags = skb_shinfo(skb)->nr_frags + 1.  In both arms the skb is mapped
into a scatterlist via skb_to_sgvec() and passed as both src and dst of
aead_request_set_crypt(), so the AEAD operates in place over the
existing frag pages.

Drop the paged-fragment arm so any non-linear inbound skb falls through
to skb_cow_data().  The fully linear fast path is unchanged and the
existing skb_cow_data() error handling that follows the gate is reused.

Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 net/ipv4/esp4.c | 13 +++----------
 net/ipv6/esp6.c | 13 +++----------
 2 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 6dfc0bcdef65..a6fbdec139dc 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -868,17 +868,10 @@ static int esp_input(struct xfrm_state *x, struct sk_buff *skb)
 		assoclen += seqhilen;
 	}
 
-	if (!skb_cloned(skb)) {
-		if (!skb_is_nonlinear(skb)) {
-			nfrags = 1;
-
-			goto skip_cow;
-		} else if (!skb_has_frag_list(skb)) {
-			nfrags = skb_shinfo(skb)->nr_frags;
-			nfrags++;
+	if (!skb_cloned(skb) && !skb_is_nonlinear(skb)) {
+		nfrags = 1;
 
-			goto skip_cow;
-		}
+		goto skip_cow;
 	}
 
 	err = skb_cow_data(skb, 0, &trailer);
diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 9f75313734f8..e5504cc0ecf9 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -910,17 +910,10 @@ static int esp6_input(struct xfrm_state *x, struct sk_buff *skb)
 		assoclen += seqhilen;
 	}
 
-	if (!skb_cloned(skb)) {
-		if (!skb_is_nonlinear(skb)) {
-			nfrags = 1;
-
-			goto skip_cow;
-		} else if (!skb_has_frag_list(skb)) {
-			nfrags = skb_shinfo(skb)->nr_frags;
-			nfrags++;
+	if (!skb_cloned(skb) && !skb_is_nonlinear(skb)) {
+		nfrags = 1;
 
-			goto skip_cow;
-		}
+		goto skip_cow;
 	}
 
 	nfrags = skb_cow_data(skb, 0, &trailer);
-- 
2.43.0