ipv6: fix race condition regarding dst->expires and dst->from.

Eric Dumazet wrote:
| Some strange crashes happen in rt6_check_expired(), with access
| to random addresses.
|
| At first glance, it looks like the RTF_EXPIRES and
| stuff added in commit 1716a96101c49186b
| (ipv6: fix problem with expired dst cache)
| are racy : same dst could be manipulated at the same time
| on different cpus.
|
| At some point, our stack believes rt->dst.from contains a dst pointer,
| while its really a jiffie value (as rt->dst.expires shares the same area
| of memory)
|
| rt6_update_expires() should be fixed, or am I missing something ?
|
| CC Neil because of https://bugzilla.redhat.com/show_bug.cgi?id=892060

Because we do not have any locks for dst_entry, we cannot change
essential structure in the entry; e.g., we cannot change reference
to other entity.

To fix this issue, split 'from' and 'expires' field in dst_entry
out of union.  Once it is 'from' is assigned in the constructor,
keep the reference until the very last stage of the life time of
the object.

Of course, it is unsafe to change 'from', so make rt6_set_from simple
just for fresh entries.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-by: Neil Horman <nhorman@tuxdriver.com>
CC: Gao Feng <gaofeng@cn.fujitsu.com>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reported-by: Steinar H. Gunderson <sesse@google.com>
Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/dst.h b/include/net/dst.h
index 3da47e0a4a1ffdfce7369980dca71c58cf1606a5..853cda11e518be98cbcf0d4bd5fa9270c804d2f5 100644 (file)
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -36,13 +36,9 @@ struct dst_entry {
        struct net_device       *dev;
        struct  dst_ops         *ops;
        unsigned long           _metrics;
-       union {
-               unsigned long           expires;
-               /* point to where the dst_entry copied from */
-               struct dst_entry        *from;
-       };
+       unsigned long           expires;
        struct dst_entry        *path;
-       void                    *__pad0;
+       struct dst_entry        *from;
 #ifdef CONFIG_XFRM
        struct xfrm_state       *xfrm;
 #else

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 6919a501f99efeceb2f24d59d6a0a4a47ade857c..2a601e7da1bfc8b97490075531975dcdfebc8370 100644 (file)
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -164,50 +164,35 @@ static inline struct inet6_dev *ip6_dst_idev(struct dst_entry *dst)
 
 static inline void rt6_clean_expires(struct rt6_info *rt)
 {
-       if (!(rt->rt6i_flags & RTF_EXPIRES) && rt->dst.from)
-               dst_release(rt->dst.from);
-
        rt->rt6i_flags &= ~RTF_EXPIRES;
-       rt->dst.from = NULL;
 }
 
 static inline void rt6_set_expires(struct rt6_info *rt, unsigned long expires)
 {
-       if (!(rt->rt6i_flags & RTF_EXPIRES) && rt->dst.from)
-               dst_release(rt->dst.from);
-
-       rt->rt6i_flags |= RTF_EXPIRES;
        rt->dst.expires = expires;
+       rt->rt6i_flags |= RTF_EXPIRES;
 }
 
-static inline void rt6_update_expires(struct rt6_info *rt, int timeout)
+static inline void rt6_update_expires(struct rt6_info *rt0, int timeout)
 {
-       if (!(rt->rt6i_flags & RTF_EXPIRES)) {
-               if (rt->dst.from)
-                       dst_release(rt->dst.from);
-               /* dst_set_expires relies on expires == 0 
-                * if it has not been set previously.
-                */
-               rt->dst.expires = 0;
-       }
-
-       dst_set_expires(&rt->dst, timeout);
-       rt->rt6i_flags |= RTF_EXPIRES;
+       struct rt6_info *rt;
+
+       for (rt = rt0; rt && !(rt->rt6i_flags & RTF_EXPIRES);
+            rt = (struct rt6_info *)rt->dst.from);
+       if (rt && rt != rt0)
+               rt0->dst.expires = rt->dst.expires;
+
+       dst_set_expires(&rt0->dst, timeout);
+       rt0->rt6i_flags |= RTF_EXPIRES;
 }
 
 static inline void rt6_set_from(struct rt6_info *rt, struct rt6_info *from)
 {
        struct dst_entry *new = (struct dst_entry *) from;
 
-       if (!(rt->rt6i_flags & RTF_EXPIRES) && rt->dst.from) {
-               if (new == rt->dst.from)
-                       return;
-               dst_release(rt->dst.from);
-       }
-
        rt->rt6i_flags &= ~RTF_EXPIRES;
-       rt->dst.from = new;
        dst_hold(new);
+       rt->dst.from = new;
 }
 
 static inline void ip6_rt_put(struct rt6_info *rt)

diff --git a/net/core/dst.c b/net/core/dst.c
index ee6153e2cf43b83abb51e96620d482e820560ca9..35fd12f1a69c38ad899a12392fcdfc768081bdb9 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -179,6 +179,7 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
        dst_init_metrics(dst, dst_default_metrics, true);
        dst->expires = 0UL;
        dst->path = dst;
+       dst->from = NULL;
 #ifdef CONFIG_XFRM
        dst->xfrm = NULL;
 #endif

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 515bb51e05a8b2f7eb5882fd2ebdf3a73fcec61e..928266569689e7624cde4206f657df495a0bdd43 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -287,6 +287,7 @@ static void ip6_dst_destroy(struct dst_entry *dst)
 {
        struct rt6_info *rt = (struct rt6_info *)dst;
        struct inet6_dev *idev = rt->rt6i_idev;
+       struct dst_entry *from = dst->from;
 
        if (!(rt->dst.flags & DST_HOST))
                dst_destroy_metrics_generic(dst);
@@ -296,8 +297,8 @@ static void ip6_dst_destroy(struct dst_entry *dst)
                in6_dev_put(idev);
        }
 
-       if (!(rt->rt6i_flags & RTF_EXPIRES) && dst->from)
-               dst_release(dst->from);
+       dst->from = NULL;
+       dst_release(from);
 
        if (rt6_has_peer(rt)) {
                struct inet_peer *peer = rt6_peer_ptr(rt);
@@ -1010,7 +1011,6 @@ struct dst_entry *ip6_blackhole_route(struct net *net, struct dst_entry *dst_ori
 
                rt->rt6i_gateway = ort->rt6i_gateway;
                rt->rt6i_flags = ort->rt6i_flags;
-               rt6_clean_expires(rt);
                rt->rt6i_metric = 0;
 
                memcpy(&rt->rt6i_dst, &ort->rt6i_dst, sizeof(struct rt6key));
@@ -1784,8 +1784,6 @@ static struct rt6_info *ip6_rt_copy(struct rt6_info *ort,
                if ((ort->rt6i_flags & (RTF_DEFAULT | RTF_ADDRCONF)) ==
                    (RTF_DEFAULT | RTF_ADDRCONF))
                        rt6_set_from(rt, ort);
-               else
-                       rt6_clean_expires(rt);
                rt->rt6i_metric = 0;
 
 #ifdef CONFIG_IPV6_SUBTREES