diff options
| author | Andrea Mayer <andrea.mayer@uniroma2.it> | 2026-04-21 11:47:35 +0200 |
|---|---|---|
| committer | Paolo Abeni <pabeni@redhat.com> | 2026-04-28 11:16:14 +0200 |
| commit | f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e (patch) | |
| tree | 0e81790227f6b8da16e5a23da87d3e65e1052c32 /net | |
| parent | 3bc179bc7146c26c9dff75d2943d10528274e301 (diff) | |
net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels
seg6_input_core() and rpl_input() call ip6_route_input() which sets a
NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking
dst_hold() unconditionally.
On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can
release the underlying pcpu_rt between the lookup and the caching
through a concurrent FIB lookup on a shared nexthop.
Simplified race sequence:
ksoftirqd/X higher-prio task (same CPU X)
----------- --------------------------------
seg6_input_core(,skb)/rpl_input(skb)
dst_cache_get()
-> miss
ip6_route_input(skb)
-> ip6_pol_route(,skb,flags)
[RT6_LOOKUP_F_DST_NOREF in flags]
-> FIB lookup resolves fib6_nh
[nhid=N route]
-> rt6_make_pcpu_route()
[creates pcpu_rt, refcount=1]
pcpu_rt->sernum = fib6_sernum
[fib6_sernum=W]
-> cmpxchg(fib6_nh.rt6i_pcpu,
NULL, pcpu_rt)
[slot was empty, store succeeds]
-> skb_dst_set_noref(skb, dst)
[dst is pcpu_rt, refcount still 1]
rt_genid_bump_ipv6()
-> bumps fib6_sernum
[fib6_sernum from W to Z]
ip6_route_output()
-> ip6_pol_route()
-> FIB lookup resolves fib6_nh
[nhid=N]
-> rt6_get_pcpu_route()
pcpu_rt->sernum != fib6_sernum
[W <> Z, stale]
-> prev = xchg(rt6i_pcpu, NULL)
-> dst_release(prev)
[prev is pcpu_rt,
refcount 1->0, dead]
dst = skb_dst(skb)
[dst is the dead pcpu_rt]
dst_cache_set_ip6(dst)
-> dst_hold() on dead dst
-> WARN / use-after-free
For the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without
PREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release
the pcpu_rt. Shared nexthop objects provide such a path, as two routes
pointing to the same nhid share the same fib6_nh and its rt6i_pcpu
entry.
Fix seg6_input_core() and rpl_input() by calling skb_dst_force() after
ip6_route_input() to force the NOREF dst into a refcounted one before
caching.
The output path is not affected as ip6_route_output() already returns a
refcounted dst.
Fixes: af4a2209b134 ("ipv6: sr: use dst_cache in seg6_input")
Fixes: a7a29f9c361f ("net: ipv6: add rpl sr tunnel")
Cc: stable@vger.kernel.org
Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
Link: https://patch.msgid.link/20260421094735.20997-1-andrea.mayer@uniroma2.it
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'net')
| -rw-r--r-- | net/ipv6/rpl_iptunnel.c | 9 | ||||
| -rw-r--r-- | net/ipv6/seg6_iptunnel.c | 9 |
2 files changed, 18 insertions, 0 deletions
diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c index c7942cf65567..4e10adcd70e8 100644 --- a/net/ipv6/rpl_iptunnel.c +++ b/net/ipv6/rpl_iptunnel.c @@ -287,7 +287,16 @@ static int rpl_input(struct sk_buff *skb) if (!dst) { ip6_route_input(skb); + + /* ip6_route_input() sets a NOREF dst; force a refcount on it + * before caching or further use. + */ + skb_dst_force(skb); dst = skb_dst(skb); + if (unlikely(!dst)) { + err = -ENETUNREACH; + goto drop; + } /* cache only if we don't create a dst reference loop */ if (!dst->error && lwtst != dst->lwtstate) { diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c index 9b64343ebad6..4c45c0a77d75 100644 --- a/net/ipv6/seg6_iptunnel.c +++ b/net/ipv6/seg6_iptunnel.c @@ -515,7 +515,16 @@ static int seg6_input_core(struct net *net, struct sock *sk, if (!dst) { ip6_route_input(skb); + + /* ip6_route_input() sets a NOREF dst; force a refcount on it + * before caching or further use. + */ + skb_dst_force(skb); dst = skb_dst(skb); + if (unlikely(!dst)) { + err = -ENETUNREACH; + goto drop; + } /* cache only if we don't create a dst reference loop */ if (!dst->error && lwtst != dst->lwtstate) { |