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Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: David Ahern , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Jiayuan Chen , Hangbin Liu X-Mailer: b4 0.14.3 All reader paths that access fib6_metrics on a shared fib6_info need READ_ONCE() annotations to prevent the compiler from reloading the pointer and producing inconsistent views. Without READ_ONCE() in the readers, the compiler may reload fib6_metrics between two uses. For example, in rt6_set_from(), ip_dst_init_metrics() is inlined and references fib_metrics twice. If the first load sees &dst_default_metrics and a subsequent load sees the newly allocated pointer p, dst->_metrics could end up incorrectly flagged, e.g. (&dst_default_metrics) | DST_METRICS_READ_ONLY | DST_METRICS_REFCOUNTED Fix all reader paths on shared fib6_info objects: Fixes: d4ead6b34b67 ("net/ipv6: move metrics from dst to rt6_info") Suggested-by: Jiayuan Chen Signed-off-by: Hangbin Liu --- include/net/ip6_fib.h | 4 +++- net/ipv6/ip6_fib.c | 6 ++++-- net/ipv6/route.c | 18 +++++++++++------- 3 files changed, 18 insertions(+), 10 deletions(-) diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h index 9f8b6814a96a..2dfb04fab5da 100644 --- a/include/net/ip6_fib.h +++ b/include/net/ip6_fib.h @@ -594,7 +594,9 @@ void fib6_update_sernum_stub(struct net *net, struct fi= b6_info *f6i); void fib6_metric_set(struct fib6_info *f6i, int metric, u32 val); static inline bool fib6_metric_locked(struct fib6_info *f6i, int metric) { - return !!(f6i->fib6_metrics->metrics[RTAX_LOCK - 1] & (1 << metric)); + struct dst_metrics *m =3D READ_ONCE(f6i->fib6_metrics); + + return !!(m->metrics[RTAX_LOCK - 1] & (1 << metric)); } void fib6_info_hw_flags_set(struct net *net, struct fib6_info *f6i, bool offload, bool trap, bool offload_failed); diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index dd26657b6a4a..3c96580c2a03 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -1144,9 +1144,11 @@ static int fib6_add_rt2node(struct fib6_node *fn, st= ruct fib6_info *rt, iter->fib6_flags &=3D ~RTF_PREFIX_RT; } =20 - if (rt->fib6_pmtu) + u32 pmtu =3D READ_ONCE(rt->fib6_pmtu); + + if (pmtu) fib6_metric_set(iter, RTAX_MTU, - rt->fib6_pmtu); + pmtu); return -EEXIST; } /* If we have the same destination and the same metric, diff --git a/net/ipv6/route.c b/net/ipv6/route.c index cb521700cee7..002a7cda9f6b 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1163,7 +1163,7 @@ static void rt6_set_from(struct rt6_info *rt, struct = fib6_info *from) { rt->rt6i_flags &=3D ~RTF_EXPIRES; rcu_assign_pointer(rt->from, from); - ip_dst_init_metrics(&rt->dst, from->fib6_metrics); + ip_dst_init_metrics(&rt->dst, READ_ONCE(from->fib6_metrics)); } =20 /* Caller must already hold reference to f6i in result */ @@ -1635,11 +1635,12 @@ __rt6_find_exception_rcu(struct rt6_exception_bucke= t **bucket, static unsigned int fib6_mtu(const struct fib6_result *res) { const struct fib6_nh *nh =3D res->nh; + struct dst_metrics *m; unsigned int mtu; =20 - if (res->f6i->fib6_pmtu) { - mtu =3D res->f6i->fib6_pmtu; - } else { + m =3D READ_ONCE(res->f6i->fib6_metrics); + mtu =3D READ_ONCE(m->metrics[RTAX_MTU - 1]); + if (!mtu) { struct net_device *dev =3D nh->fib_nh_dev; struct inet6_dev *idev; =20 @@ -3300,7 +3301,9 @@ u32 ip6_mtu_from_fib6(const struct fib6_result *res, u32 mtu =3D 0; =20 if (unlikely(fib6_metric_locked(f6i, RTAX_MTU))) { - mtu =3D f6i->fib6_pmtu; + struct dst_metrics *m =3D READ_ONCE(f6i->fib6_metrics); + + mtu =3D READ_ONCE(m->metrics[RTAX_MTU - 1]); if (mtu) goto out; } @@ -5037,7 +5040,8 @@ static int fib6_nh_mtu_change(struct fib6_nh *nh, voi= d *_arg) */ if (nh->fib_nh_dev =3D=3D arg->dev) { struct inet6_dev *idev =3D __in6_dev_get(arg->dev); - u32 mtu =3D f6i->fib6_pmtu; + struct dst_metrics *m =3D READ_ONCE(f6i->fib6_metrics); + u32 mtu =3D READ_ONCE(m->metrics[RTAX_MTU - 1]); =20 if (mtu >=3D arg->mtu || (mtu < arg->mtu && mtu =3D=3D idev->cnf.mtu6)) @@ -5844,7 +5848,7 @@ static int rt6_fill_node(struct net *net, struct sk_b= uff *skb, goto nla_put_failure; } =20 - pmetrics =3D dst ? dst_metrics_ptr(dst) : rt->fib6_metrics->metrics; + pmetrics =3D dst ? dst_metrics_ptr(dst) : READ_ONCE(rt->fib6_metrics)->me= trics; if (rtnetlink_put_metrics(skb, pmetrics) < 0) goto nla_put_failure; =20 --- base-commit: 48b3cd69265f346f64b93064723492da46206e9b change-id: 20260401-fib6_metric_read_once-72f2bba54a02 Best regards, --=20 Hangbin Liu