esp: Fix possible buffer overflow in ESP transformation

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>

diff --git a/include/net/esp.h b/include/net/esp.h
index 9c5637d41d95168052686caf7b3ff51b517e6b9b..90cd02ff77ef67f7f65e2c53127c4510c23bd4a9 100644 (file)
--- 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 << SKB_FRAG_PAGE_ORDER)
+
 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 e1b1d080e908d4b13561e641cb21437686db6cee..70e6c87fbe3df15c5ca6adc68b685e3a2afa21a4 100644 (file)
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -446,6 +446,7 @@ int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
        struct page *page;
        struct sk_buff *trailer;
        int tailen = esp->tailen;
+       unsigned int allocsz;
 
        /* this is non-NULL only with TCP/UDP Encapsulation */
        if (x->encap) {
@@ -455,6 +456,10 @@ int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
                        return err;
        }
 
+       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 7591160edce14d4eb75abdf5c2d72099ea92ae68..b0ffbcd5432d67f584a94ccb79712eb9203a1313 100644 (file)
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -482,6 +482,7 @@ int esp6_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info
        struct page *page;
        struct sk_buff *trailer;
        int tailen = esp->tailen;
+       unsigned int allocsz;
 
        if (x->encap) {
                int err = esp6_output_encap(x, skb, esp);
@@ -490,6 +491,10 @@ int esp6_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info
                        return err;
        }
 
+       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;