From ebe48d368e97d007bfeb76fcb065d6cfc4c96645 Mon Sep 17 00:00:00 2001
From: Steffen Klassert <steffen.klassert@secunet.com>
Date: Mon, 7 Mar 2022 13:11:39 +0100
Subject: [PATCH] esp: Fix possible buffer overflow in ESP transformation
Patch-mainline: v5.17-rc8
Git-commit: ebe48d368e97d007bfeb76fcb065d6cfc4c96645
References: bsc#1197131 CVE-2022-0886

The maximum message size that can be send is bigger than
the  maximum site that skb_page_frag_refill can allocate.
So it is possible to write beyond the allocated buffer.

Fix this by doing a fallback to COW in that case.

v2:

Avoid get get_order() costs as suggested by Linus Torvalds.

Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible")
Reported-by: valis <sec@valis.email>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Denis Kirjanov <dkirjanov@suse.de>
---
 include/net/esp.h | 2 ++
 net/ipv4/esp4.c   | 5 +++++
 net/ipv6/esp6.c   | 5 +++++
 3 files changed, 12 insertions(+)

diff --git a/include/net/esp.h b/include/net/esp.h
index 9c5637d41d95..90cd02ff77ef 100644
--- a/include/net/esp.h
+++ b/include/net/esp.h
@@ -4,6 +4,8 @@
 
 #include <linux/skbuff.h>
 
+#define ESP_SKB_FRAG_MAXSIZE (PAGE_SIZE << get_order(32768))
+
 struct ip_esp_hdr;
 
 static inline struct ip_esp_hdr *ip_esp_hdr(const struct sk_buff *skb)
diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index e1b1d080e908..70e6c87fbe3d 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -252,11 +252,16 @@ int esp_output_head(struct xfrm_state *x
 	struct page *page;
 	struct sk_buff *trailer;
 	int tailen = esp->tailen;
+	unsigned int allocsz;
 
 	/* this is non-NULL only with UDP Encapsulation */
 	if (x->encap)
 		esp_output_udp_encap(x, skb, esp);
 
+	allocsz = ALIGN(skb->data_len + tailen, L1_CACHE_BYTES);
+	if (allocsz > ESP_SKB_FRAG_MAXSIZE)
+		goto cow;
+
 	if (!skb_cloned(skb)) {
 		if (tailen <= skb_tailroom(skb)) {
 			nfrags = 1;
diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 7591160edce1..b0ffbcd5432d 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -227,9 +227,14 @@ int esp6_output_head(struct xfrm_state *
 	struct ip_esp_hdr *esph;
 	struct sk_buff *trailer;
 	int tailen = esp->tailen;
+	unsigned int allocsz;
 
 	esph = ip_esp_hdr(skb);
 
+	allocsz = ALIGN(skb->data_len + tailen, L1_CACHE_BYTES);
+	if (allocsz > ESP_SKB_FRAG_MAXSIZE)
+		goto cow;
+
 	if (!skb_cloned(skb)) {
 		if (tailen <= skb_tailroom(skb)) {
 			nfrags = 1;
-- 
2.16.4