[PATCH v2,net-next 1/2] ip_gre: fix parsing gre header in ipgre_err

gre_parse_header stops parsing when csum_err is encountered, which means
tpi->key is undefined and ip_tunnel_lookup will return NULL improperly.

This patch introduce a NULL pointer as csum_err parameter. Even when
csum_err is encountered, it won't return error and continue parsing gre
header as expected.

Fixes: 9f57c67c379d ("gre: Remove support for sharing GRE protocol hook.")
Reported-by: Jiri Benc <redacted>
Signed-off-by: Haishuang Yan <redacted>
---
 net/ipv4/gre_demux.c | 2 +-
 net/ipv4/ip_gre.c    | 9 +++------
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index b798862..679a527 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c

@@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 
 	options = (__be32 *)(greh + 1);
 	if (greh->flags & GRE_CSUM) {
-		if (skb_checksum_simple_validate(skb)) {
+		if (csum_err && skb_checksum_simple_validate(skb)) {
 			*csum_err = true;
 			return -EINVAL;
 		}

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 8cce0e9..c3385a8 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c

@@ -232,13 +232,10 @@ static void gre_err(struct sk_buff *skb, u32 info)
 	const int type = icmp_hdr(skb)->type;
 	const int code = icmp_hdr(skb)->code;
 	struct tnl_ptk_info tpi;
-	bool csum_err = false;
 
-	if (gre_parse_header(skb, &tpi, &csum_err, htons(ETH_P_IP),
-			     iph->ihl * 4) < 0) {
-		if (!csum_err)		/* ignore csum errors. */
-			return;
-	}
+	if (gre_parse_header(skb, &tpi, NULL, htons(ETH_P_IP),
+			     iph->ihl * 4) < 0)
+		return;
 
 	if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED) {
 		ipv4_update_pmtu(skb, dev_net(skb->dev), info,

-- 
1.8.3.1

Same as ip_gre, use gre_parse_header to parse gre header in gre error
handler code.

Signed-off-by: Haishuang Yan <redacted>
---
 net/ipv6/ip6_gre.c | 26 ++++----------------------
 1 file changed, 4 insertions(+), 22 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index e493b04..515adbd 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c

@@ -427,35 +427,17 @@ static void ip6gre_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		       u8 type, u8 code, int offset, __be32 info)
 {
 	struct net *net = dev_net(skb->dev);
-	const struct gre_base_hdr *greh;
 	const struct ipv6hdr *ipv6h;
-	int grehlen = sizeof(*greh);
+	struct tnl_ptk_info tpi;
 	struct ip6_tnl *t;
-	int key_off = 0;
-	__be16 flags;
-	__be32 key;
 
-	if (!pskb_may_pull(skb, offset + grehlen))
-		return;
-	greh = (const struct gre_base_hdr *)(skb->data + offset);
-	flags = greh->flags;
-	if (flags & (GRE_VERSION | GRE_ROUTING))
+	if (gre_parse_header(skb, &tpi, NULL, htons(ETH_P_IPV6),
+			     offset) < 0)
 		return;
-	if (flags & GRE_CSUM)
-		grehlen += 4;
-	if (flags & GRE_KEY) {
-		key_off = grehlen + offset;
-		grehlen += 4;
-	}
 
-	if (!pskb_may_pull(skb, offset + grehlen))
-		return;
 	ipv6h = (const struct ipv6hdr *)skb->data;
-	greh = (const struct gre_base_hdr *)(skb->data + offset);
-	key = key_off ? *(__be32 *)(skb->data + key_off) : 0;
-
 	t = ip6gre_tunnel_lookup(skb->dev, &ipv6h->daddr, &ipv6h->saddr,
-				 key, greh->protocol);
+				 tpi.key, tpi.proto);
 	if (!t)
 		return;
 

-- 
1.8.3.1

From: Haishuang Yan <redacted>
Date: Wed, 12 Sep 2018 17:21:21 +0800

You want to ignore csum errors, but you do not want to elide the side
effects of the skb_checksum_simple_validate() call which are to set
skb->csum_valid and skb->csum.

Therefore, the skb_checksum_simple_validate() call still needs to be
performed. We just wont return -EINVAL in the NULL csum_err case.

On 2018年9月14日, at 上午1:58, David Miller [off-list ref] wrote:

From: Haishuang Yan <redacted>
Date: Wed, 12 Sep 2018 17:21:21 +0800

quoted

@@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,

	options = (__be32 *)(greh + 1);
	if (greh->flags & GRE_CSUM) {
-		if (skb_checksum_simple_validate(skb)) {
+		if (csum_err && skb_checksum_simple_validate(skb)) {
			*csum_err = true;
			return -EINVAL;
		}

You want to ignore csum errors, but you do not want to elide the side
effects of the skb_checksum_simple_validate() call which are to set
skb->csum_valid and skb->csum.

Therefore, the skb_checksum_simple_validate() call still needs to be
performed. We just wont return -EINVAL in the NULL csum_err case.

How about doing like this:

--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c

@@ -86,13 +86,14 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,

        options = (__be32 *)(greh + 1);
        if (greh->flags & GRE_CSUM) {
-               if (skb_checksum_simple_validate(skb)) {
+               if (!skb_checksum_simple_validate(skb)) {
+                       skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
+                                                null_compute_pseudo);
+               } else if (csum_err) {
                        *csum_err = true;
                        return -EINVAL;
                }

-               skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
-                                        null_compute_pseudo);

Thanks for reviewing.

On 13/09/18 18:58, David Miller wrote:

From: Haishuang Yan <redacted>
Date: Wed, 12 Sep 2018 17:21:21 +0800

quoted

@@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 
 	options = (__be32 *)(greh + 1);
 	if (greh->flags & GRE_CSUM) {
-		if (skb_checksum_simple_validate(skb)) {
+		if (csum_err && skb_checksum_simple_validate(skb)) {
 			*csum_err = true;
 			return -EINVAL;
 		}

You want to ignore csum errors, but you do not want to elide the side
effects of the skb_checksum_simple_validate() call which are to set
skb->csum_valid and skb->csum.

Therefore, the skb_checksum_simple_validate() call still needs to be
performed. We just wont return -EINVAL in the NULL csum_err case.

How about just reversing the order of the AND?

	if (skb_checksum_simple_validate(skb) && csum_err) {
		*csum_err = true;
		return -EINVAL;
	}

On 2018年9月14日, at 下午8:44, Edward Cree [off-list ref] wrote:

On 13/09/18 18:58, David Miller wrote:

quoted

From: Haishuang Yan <redacted>
Date: Wed, 12 Sep 2018 17:21:21 +0800

quoted

@@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,

	options = (__be32 *)(greh + 1);
	if (greh->flags & GRE_CSUM) {
-		if (skb_checksum_simple_validate(skb)) {
+		if (csum_err && skb_checksum_simple_validate(skb)) {
			*csum_err = true;
			return -EINVAL;
		}

You want to ignore csum errors, but you do not want to elide the side
effects of the skb_checksum_simple_validate() call which are to set
skb->csum_valid and skb->csum.

Therefore, the skb_checksum_simple_validate() call still needs to be
performed. We just wont return -EINVAL in the NULL csum_err case.

How about just reversing the order of the AND?

	if (skb_checksum_simple_validate(skb) && csum_err) {
		*csum_err = true;
		return -EINVAL;
	}

It looks good to me, thanks!

But skb_checksum_try_convert only need to be called after the checksum is 
validated, so I suggested a better solution as following:

   89                 if (!skb_checksum_simple_validate(skb)) {
   90                         skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
   91                                                  null_compute_pseudo);
   92                 } else if (csum_err) {
   93                         *csum_err = true;
   94                         return -EINVAL;
   95                 }