net: fix __dst_negative_advice() race

commit 92f1655aa2b2294d0b49925f3b875a634bd3b59e upstream.

__dst_negative_advice() does not enforce proper RCU rules when
sk->dst_cache must be cleared, leading to possible UAF.

RCU rules are that we must first clear sk->sk_dst_cache,
then call dst_release(old_dst).

Note that sk_dst_reset(sk) is implementing this protocol correctly,
while __dst_negative_advice() uses the wrong order.

Given that ip6_negative_advice() has special logic
against RTF_CACHE, this means each of the three ->negative_advice()
existing methods must perform the sk_dst_reset() themselves.

Note the check against NULL dst is centralized in
__dst_negative_advice(), there is no need to duplicate
it in various callbacks.

Many thanks to Clement Lecigne for tracking this issue.

This old bug became visible after the blamed commit, using UDP sockets.

Fixes: a87cb3e48ee8 ("net: Facility to report route quality of connected sockets")
Reported-by: Clement Lecigne <clecigne@google.com>
Diagnosed-by: Clement Lecigne <clecigne@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240528114353.1794151-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[Lee: Stable backport]
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
index 632086b2f644a90f38f2382111c5f0430aff0e8b..3ae2fda29507382ff83867ed5898f433bb38783a 100644 (file)
--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -24,7 +24,7 @@ struct dst_ops {
        void                    (*destroy)(struct dst_entry *);
        void                    (*ifdown)(struct dst_entry *,
                                          struct net_device *dev, int how);
-       struct dst_entry *      (*negative_advice)(struct dst_entry *);
+       void                    (*negative_advice)(struct sock *sk, struct dst_entry *);
        void                    (*link_failure)(struct sk_buff *);
        void                    (*update_pmtu)(struct dst_entry *dst, struct sock *sk,
                                               struct sk_buff *skb, u32 mtu,

diff --git a/include/net/sock.h b/include/net/sock.h
index 8d592df7251f813ddfd299ef18813325a3ba9bc1..250d5a6c508cb66962caf00432d090528aca2968 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1938,19 +1938,12 @@ sk_dst_get(struct sock *sk)
 
 static inline void dst_negative_advice(struct sock *sk)
 {
-       struct dst_entry *ndst, *dst = __sk_dst_get(sk);
+       struct dst_entry *dst = __sk_dst_get(sk);
 
        sk_rethink_txhash(sk);
 
-       if (dst && dst->ops->negative_advice) {
-               ndst = dst->ops->negative_advice(dst);
-
-               if (ndst != dst) {
-                       rcu_assign_pointer(sk->sk_dst_cache, ndst);
-                       sk_tx_queue_clear(sk);
-                       WRITE_ONCE(sk->sk_dst_pending_confirm, 0);
-               }
-       }
+       if (dst && dst->ops->negative_advice)
+               dst->ops->negative_advice(sk, dst);
 }
 
 static inline void

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 5b008d838e2b94b0a3845ff0648433d0d03f0c90..2672b71e662d34e65c1a3b376bde9ec987434e30 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -137,7 +137,8 @@ static int ip_rt_gc_timeout __read_mostly   = RT_GC_TIMEOUT;
 static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie);
 static unsigned int     ipv4_default_advmss(const struct dst_entry *dst);
 static unsigned int     ipv4_mtu(const struct dst_entry *dst);
-static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst);
+static void            ipv4_negative_advice(struct sock *sk,
+                                            struct dst_entry *dst);
 static void             ipv4_link_failure(struct sk_buff *skb);
 static void             ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
                                           struct sk_buff *skb, u32 mtu,
@@ -856,22 +857,15 @@ static void ip_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_buf
        __ip_do_redirect(rt, skb, &fl4, true);
 }
 
-static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
+static void ipv4_negative_advice(struct sock *sk,
+                                struct dst_entry *dst)
 {
        struct rtable *rt = (struct rtable *)dst;
-       struct dst_entry *ret = dst;
 
-       if (rt) {
-               if (dst->obsolete > 0) {
-                       ip_rt_put(rt);
-                       ret = NULL;
-               } else if ((rt->rt_flags & RTCF_REDIRECTED) ||
-                          rt->dst.expires) {
-                       ip_rt_put(rt);
-                       ret = NULL;
-               }
-       }
-       return ret;
+       if ((dst->obsolete > 0) ||
+           (rt->rt_flags & RTCF_REDIRECTED) ||
+           rt->dst.expires)
+               sk_dst_reset(sk);
 }
 
 /*

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f2c8845eaa5e3a2835507c99c177220777923b47..3917755351ad94c55d6550b23ede2ea5285c000d 100644 (file)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -84,7 +84,8 @@ enum rt6_nud_state {
 static struct dst_entry        *ip6_dst_check(struct dst_entry *dst, u32 cookie);
 static unsigned int     ip6_default_advmss(const struct dst_entry *dst);
 static unsigned int     ip6_mtu(const struct dst_entry *dst);
-static struct dst_entry *ip6_negative_advice(struct dst_entry *);
+static void            ip6_negative_advice(struct sock *sk,
+                                           struct dst_entry *dst);
 static void            ip6_dst_destroy(struct dst_entry *);
 static void            ip6_dst_ifdown(struct dst_entry *,
                                       struct net_device *dev, int how);
@@ -2658,24 +2659,24 @@ static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
        return dst_ret;
 }
 
-static struct dst_entry *ip6_negative_advice(struct dst_entry *dst)
+static void ip6_negative_advice(struct sock *sk,
+                               struct dst_entry *dst)
 {
        struct rt6_info *rt = (struct rt6_info *) dst;
 
-       if (rt) {
-               if (rt->rt6i_flags & RTF_CACHE) {
-                       rcu_read_lock();
-                       if (rt6_check_expired(rt)) {
-                               rt6_remove_exception_rt(rt);
-                               dst = NULL;
-                       }
-                       rcu_read_unlock();
-               } else {
-                       dst_release(dst);
-                       dst = NULL;
+       if (rt->rt6i_flags & RTF_CACHE) {
+               rcu_read_lock();
+               if (rt6_check_expired(rt)) {
+                       /* counteract the dst_release() in sk_dst_reset() */
+                       dst_hold(dst);
+                       sk_dst_reset(sk);
+
+                       rt6_remove_exception_rt(rt);
                }
+               rcu_read_unlock();
+               return;
        }
-       return dst;
+       sk_dst_reset(sk);
 }
 
 static void ip6_link_failure(struct sk_buff *skb)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 9484f27e905ae89c2fce5d66f7f9ed34cfcb1e3b..bffac2f4b581d255c2e24daee63a933fc1f44fbd 100644 (file)
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3772,15 +3772,10 @@ static void xfrm_link_failure(struct sk_buff *skb)
        /* Impossible. Such dst must be popped before reaches point of failure. */
 }
 
-static struct dst_entry *xfrm_negative_advice(struct dst_entry *dst)
+static void xfrm_negative_advice(struct sock *sk, struct dst_entry *dst)
 {
-       if (dst) {
-               if (dst->obsolete) {
-                       dst_release(dst);
-                       dst = NULL;
-               }
-       }
-       return dst;
+       if (dst->obsolete)
+               sk_dst_reset(sk);
 }
 
 static void xfrm_init_pmtu(struct xfrm_dst **bundle, int nr)