[Devel] [PATCH RHEL7 COMMIT] ms/net: Fix usage of pskb_trim_rcsum

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.6.1.vz7.171.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.6.1.vz7.171.4
------>
commit 36a0097fafb6b00c33a9b5497eda51cafa6972aa
Author: Ross Lagerwall <ross.lagerwall at citrix.com>
Date:   Tue Dec 15 12:24:33 2020 +0300

    ms/net: Fix usage of pskb_trim_rcsum
    
    In certain cases, pskb_trim_rcsum() may change skb pointers.
    Reinitialize header pointers afterwards to avoid potential
    use-after-frees. Add a note in the documentation of
    pskb_trim_rcsum(). Found by KASAN.
    
    Signed-off-by: Ross Lagerwall <ross.lagerwall at citrix.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    (cherry-picked from commit 6c57f0458022298e4da1729c67bd33ce41c14e7a)
    https://jira.sw.ru/browse/PSBM-123062
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 drivers/net/ppp/pppoe.c                  | 1 +
 include/linux/skbuff.h                   | 1 +
 net/bridge/br_netfilter_ipv6.c           | 1 +
 net/bridge/netfilter/nft_reject_bridge.c | 1 +
 net/ipv4/ip_input.c                      | 1 +
 5 files changed, 5 insertions(+)

diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index 15d3f44..3101720 100644
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -442,6 +442,7 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (pskb_trim_rcsum(skb, len))
 		goto drop;
 
+	ph = pppoe_hdr(skb);
 	pn = pppoe_pernet(dev_net(dev));
 	if (!pn) /* no VE_FEATURE_PPP */
 		goto drop;
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index c39936f..296e734 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3099,6 +3099,7 @@ static inline void *skb_push_rcsum(struct sk_buff *skb, unsigned int len)
  *
  *	This is exactly the same as pskb_trim except that it ensures the
  *	checksum of received packets are still valid after the operation.
+ *	It can change skb pointers.
  */
 
 static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
diff --git a/net/bridge/br_netfilter_ipv6.c b/net/bridge/br_netfilter_ipv6.c
index 2d8de1d..ca93162 100644
--- a/net/bridge/br_netfilter_ipv6.c
+++ b/net/bridge/br_netfilter_ipv6.c
@@ -132,6 +132,7 @@ int br_validate_ipv6(struct sk_buff *skb)
 					 IPSTATS_MIB_INDISCARDS);
 			goto drop;
 		}
+		hdr = ipv6_hdr(skb);
 	}
 	if (hdr->nexthdr == NEXTHDR_HOP && br_nf_check_hbh_len(skb))
 		goto drop;
diff --git a/net/bridge/netfilter/nft_reject_bridge.c b/net/bridge/netfilter/nft_reject_bridge.c
index 634068b..0315584 100644
--- a/net/bridge/netfilter/nft_reject_bridge.c
+++ b/net/bridge/netfilter/nft_reject_bridge.c
@@ -189,6 +189,7 @@ static bool reject6_br_csum_ok(struct sk_buff *skb, int hook)
 	    pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
 		return false;
 
+	ip6h = ipv6_hdr(skb);
 	thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
 	if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 		return false;
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index 2b97550..f537e32 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -450,6 +450,7 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
 		goto drop;
 	}
 
+	iph = ip_hdr(skb);
 	skb->transport_header = skb->network_header + iph->ihl*4;
 
 	/* Remove any debris in the socket control block */