ipv4: restore rt->fi for reference counting
IPv4 dst could use fi->fib_metrics to store metrics but fib_info itself is refcnt'ed, so without taking a refcnt fi and fi->fib_metrics could be freed while dst metrics still points to it. This triggers use-after-free as reported by Andrey twice. This patch reverts commit2860583fe8
("ipv4: Kill rt->fi") to restore this reference counting. It is a quick fix for -net and -stable, for -net-next, as Eric suggested, we can consider doing reference counting for metrics itself instead of relying on fib_info. IPv6 is very different, it copies or steals the metrics from mx6_config in fib6_commit_metrics() so probably doesn't need a refcnt. Decnet has already done the refcnt'ing, see dn_fib_semantic_match(). Fixes:2860583fe8
("ipv4: Kill rt->fi") Reported-by: Andrey Konovalov <andreyknvl@google.com> Tested-by: Andrey Konovalov <andreyknvl@google.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -69,6 +69,7 @@ struct rtable {
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struct list_head rt_uncached;
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struct uncached_list *rt_uncached_list;
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struct fib_info *fi; /* for refcnt to shared metrics */
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};
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static inline bool rt_is_input_route(const struct rtable *rt)
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@ -1387,6 +1387,11 @@ static void ipv4_dst_destroy(struct dst_entry *dst)
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{
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struct rtable *rt = (struct rtable *) dst;
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if (rt->fi) {
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fib_info_put(rt->fi);
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rt->fi = NULL;
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}
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if (!list_empty(&rt->rt_uncached)) {
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struct uncached_list *ul = rt->rt_uncached_list;
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@ -1424,6 +1429,16 @@ static bool rt_cache_valid(const struct rtable *rt)
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!rt_is_expired(rt);
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}
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static void rt_init_metrics(struct rtable *rt, struct fib_info *fi)
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{
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if (fi->fib_metrics != (u32 *)dst_default_metrics) {
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fib_info_hold(fi);
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rt->fi = fi;
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}
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dst_init_metrics(&rt->dst, fi->fib_metrics, true);
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}
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static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
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const struct fib_result *res,
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struct fib_nh_exception *fnhe,
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@ -1438,7 +1453,7 @@ static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
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rt->rt_gateway = nh->nh_gw;
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rt->rt_uses_gateway = 1;
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}
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dst_init_metrics(&rt->dst, fi->fib_metrics, true);
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rt_init_metrics(rt, fi);
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#ifdef CONFIG_IP_ROUTE_CLASSID
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rt->dst.tclassid = nh->nh_tclassid;
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#endif
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@ -1490,6 +1505,7 @@ struct rtable *rt_dst_alloc(struct net_device *dev,
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rt->rt_gateway = 0;
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rt->rt_uses_gateway = 0;
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rt->rt_table_id = 0;
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rt->fi = NULL;
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INIT_LIST_HEAD(&rt->rt_uncached);
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rt->dst.output = ip_output;
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