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Subject[PATCH AUTOSEL 4.14 04/16] esp4: add length check for UDP encapsulation
Date
From: Sabrina Dubroca <sd@queasysnail.net>

[ Upstream commit 8dfb4eba4100e7cdd161a8baef2d8d61b7a7e62e ]

esp_output_udp_encap can produce a length that doesn't fit in the 16
bits of a UDP header's length field. In that case, we'll send a
fragmented packet whose length is larger than IP_MAX_MTU (resulting in
"Oversized IP packet" warnings on receive) and with a bogus UDP
length.

To prevent this, add a length check to esp_output_udp_encap and return
-EMSGSIZE on failure.

This seems to be older than git history.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/esp4.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index d30285c5d52dd..c8e32f167ebbf 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -205,7 +205,7 @@ static void esp_output_fill_trailer(u8 *tail, int tfclen, int plen, __u8 proto)
tail[plen - 1] = proto;
}

-static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
+static int esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
{
int encap_type;
struct udphdr *uh;
@@ -213,6 +213,7 @@ static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, stru
__be16 sport, dport;
struct xfrm_encap_tmpl *encap = x->encap;
struct ip_esp_hdr *esph = esp->esph;
+ unsigned int len;

spin_lock_bh(&x->lock);
sport = encap->encap_sport;
@@ -220,11 +221,14 @@ static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, stru
encap_type = encap->encap_type;
spin_unlock_bh(&x->lock);

+ len = skb->len + esp->tailen - skb_transport_offset(skb);
+ if (len + sizeof(struct iphdr) >= IP_MAX_MTU)
+ return -EMSGSIZE;
+
uh = (struct udphdr *)esph;
uh->source = sport;
uh->dest = dport;
- uh->len = htons(skb->len + esp->tailen
- - skb_transport_offset(skb));
+ uh->len = htons(len);
uh->check = 0;

switch (encap_type) {
@@ -241,6 +245,8 @@ static void esp_output_udp_encap(struct xfrm_state *x, struct sk_buff *skb, stru

*skb_mac_header(skb) = IPPROTO_UDP;
esp->esph = esph;
+
+ return 0;
}

int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
@@ -254,8 +260,12 @@ int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
int tailen = esp->tailen;

/* this is non-NULL only with UDP Encapsulation */
- if (x->encap)
- esp_output_udp_encap(x, skb, esp);
+ if (x->encap) {
+ int err = esp_output_udp_encap(x, skb, esp);
+
+ if (err < 0)
+ return err;
+ }

if (!skb_cloned(skb)) {
if (tailen <= skb_tailroom(skb)) {
--
2.20.1
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