| Message ID | 20180713054050.5656-1-bhole_prashant_q7@lab.ntt.co.jp |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net-next] net: ip6_gre: get ipv6hdr after skb_cow_head() | expand |
On 7/12/2018 10:40 PM, Prashant Bhole wrote: > 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> Good catch. LGTM Reviewed-by: Greg Rose <gvrose8192@gmail.com> > --- > net/ipv6/ip6_gre.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c > index 367177786e34..fc7dd3a04360 100644 > --- a/net/ipv6/ip6_gre.c > +++ b/net/ipv6/ip6_gre.c > @@ -927,7 +927,6 @@ static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff *skb, > 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; > @@ -1012,6 +1011,8 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb, > 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));
On Thu, Jul 12, 2018 at 10:40 PM, Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp> wrote: > 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> > --- Thanks for the fix. Acked-by: William Tu <u9012063@gmail.com>
From: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp> Date: Fri, 13 Jul 2018 14:40:50 +0900 > 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> This bug goes back to 4.16, therefore applied to 'net' and queued up for -stable. Please do not submit bug fixes against 'net-next' in this situation in the future. Thanks.
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index 367177786e34..fc7dd3a04360 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -927,7 +927,6 @@ static netdev_tx_t ip6gre_tunnel_xmit(struct sk_buff *skb, 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; @@ -1012,6 +1011,8 @@ static netdev_tx_t ip6erspan_tunnel_xmit(struct sk_buff *skb, 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));
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> --- net/ipv6/ip6_gre.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)