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authorHangbin Liu <liuhangbin@gmail.com>2019-08-22 22:19:49 +0800
committerDavid S. Miller <davem@davemloft.net>2019-08-24 14:49:35 -0700
commitc3b4c3a47e05d5fecf7354d75824a9d1b37f3e84 (patch)
treeec5d12292cf8240d176fd748b753db0c321a35bb
parente2c693934194fd3b4e795635934883354c06ebc9 (diff)
xfrm/xfrm_policy: fix dst dev null pointer dereference in collect_md mode
In decode_session{4,6} there is a possibility that the skb dst dev is NULL, e,g, with tunnel collect_md mode, which will cause kernel crash. Here is what the code path looks like, for GRE: - ip6gre_tunnel_xmit - ip6gre_xmit_ipv6 - __gre6_xmit - ip6_tnl_xmit - if skb->len - t->tun_hlen - eth_hlen > mtu; return -EMSGSIZE - icmpv6_send - icmpv6_route_lookup - xfrm_decode_session_reverse - decode_session4 - oif = skb_dst(skb)->dev->ifindex; <-- here - decode_session6 - oif = skb_dst(skb)->dev->ifindex; <-- here The reason is __metadata_dst_init() init dst->dev to NULL by default. We could not fix it in __metadata_dst_init() as there is no dev supplied. On the other hand, the skb_dst(skb)->dev is actually not needed as we called decode_session{4,6} via xfrm_decode_session_reverse(), so oif is not used by: fl4->flowi4_oif = reverse ? skb->skb_iif : oif; So make a dst dev check here should be clean and safe. v4: No changes. v3: No changes. v2: fix the issue in decode_session{4,6} instead of updating shared dst dev in {ip_md, ip6}_tunnel_xmit. Fixes: 8d79266bc48c ("ip6_tunnel: add collect_md mode to IPv6 tunnels") Signed-off-by: Hangbin Liu <liuhangbin@gmail.com> Tested-by: Jonathan Lemon <jonathan.lemon@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/xfrm/xfrm_policy.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 8ca637a72697..ec94f5795ea4 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3269,7 +3269,7 @@ decode_session4(struct sk_buff *skb, struct flowi *fl, bool reverse)
struct flowi4 *fl4 = &fl->u.ip4;
int oif = 0;
- if (skb_dst(skb))
+ if (skb_dst(skb) && skb_dst(skb)->dev)
oif = skb_dst(skb)->dev->ifindex;
memset(fl4, 0, sizeof(struct flowi4));
@@ -3387,7 +3387,7 @@ decode_session6(struct sk_buff *skb, struct flowi *fl, bool reverse)
nexthdr = nh[nhoff];
- if (skb_dst(skb))
+ if (skb_dst(skb) && skb_dst(skb)->dev)
oif = skb_dst(skb)->dev->ifindex;
memset(fl6, 0, sizeof(struct flowi6));