4.17-stable review patch. If anyone has any objections, please let me know.
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From: Prashant Bhole bhole_prashant_q7@lab.ntt.co.jp
[ Upstream commit b7ed879425be371905d856410d19e9a42a62bcf3 ]
A KASAN:use-after-free bug was found related to ip6-erspan while running selftests/net/ip6_gre_headroom.sh
It happens because of following sequence: - ipv6hdr pointer is obtained from skb - skb_cow_head() is called, skb->head memory is reallocated - old data is accessed using ipv6hdr pointer
skb_cow_head() call was added in e41c7c68ea77 ("ip6erspan: make sure enough headroom at xmit."), but looking at the history there was a chance of similar bug because gre_handle_offloads() and pskb_trim() can also reallocate skb->head memory. Fixes tag points to commit which introduced possibility of this bug.
This patch moves ipv6hdr pointer assignment after skb_cow_head() call.
Fixes: 5a963eb61b7c ("ip6_gre: Add ERSPAN native tunnel support") Signed-off-by: Prashant Bhole bhole_prashant_q7@lab.ntt.co.jp Reviewed-by: Greg Rose gvrose8192@gmail.com Acked-by: William Tu u9012063@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/ip6_gre.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -927,7 +927,6 @@ tx_err: static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb, struct net_device *dev) { - struct ipv6hdr *ipv6h = ipv6_hdr(skb); struct ip6_tnl *t = netdev_priv(dev); struct dst_entry *dst = skb_dst(skb); struct net_device_stats *stats; @@ -998,6 +997,8 @@ static netdev_tx_t ip6erspan_tunnel_xmit goto tx_err; } } else { + struct ipv6hdr *ipv6h = ipv6_hdr(skb); + switch (skb->protocol) { case htons(ETH_P_IP): memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));