inet: frags: flush pending skbs in fqdir_pre_exit()

We have been seeing occasional deadlocks on pernet_ops_rwsem since
September in NIPA. The stuck task was usually modprobe (often loading
a driver like ipvlan), trying to take the lock as a Writer.
lockdep does not track readers for rwsems so the read wasn't obvious
from the reports.

On closer inspection the Reader holding the lock was conntrack looping
forever in nf_conntrack_cleanup_net_list(). Based on past experience
with occasional NIPA crashes I looked thru the tests which run before
the crash and noticed that the crash follows ip_defrag.sh. An immediate
red flag. Scouring thru (de)fragmentation queues reveals skbs sitting
around, holding conntrack references.

The problem is that since conntrack depends on nf_defrag_ipv6,
nf_defrag_ipv6 will load first. Since nf_defrag_ipv6 loads first its
netns exit hooks run _after_ conntrack's netns exit hook.

Flush all fragment queue SKBs during fqdir_pre_exit() to release
conntrack references before conntrack cleanup runs. Also flush
the queues in timer expiry handlers when they discover fqdir->dead
is set, in case packet sneaks in while we're running the pre_exit
flush.

The commit under Fixes is not exactly the culprit, but I think
previously the timer firing would eventually unblock the spinning
conntrack.

Fixes: d5dd88794a13 ("inet: fix various use-after-free in defrags units")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251207010942.1672972-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 3ffaceee7bbc0a88d657587adef4bf9b08c9ea78..365925c9d26286b4f25cf2b4d6b29b0b55335919 100644 (file)
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -123,18 +123,7 @@ void inet_frags_fini(struct inet_frags *);
 
 int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net);
 
-static inline void fqdir_pre_exit(struct fqdir *fqdir)
-{
-       /* Prevent creation of new frags.
-        * Pairs with READ_ONCE() in inet_frag_find().
-        */
-       WRITE_ONCE(fqdir->high_thresh, 0);
-
-       /* Pairs with READ_ONCE() in inet_frag_kill(), ip_expire()
-        * and ip6frag_expire_frag_queue().
-        */
-       WRITE_ONCE(fqdir->dead, true);
-}
+void fqdir_pre_exit(struct fqdir *fqdir);
 void fqdir_exit(struct fqdir *fqdir);
 
 void inet_frag_kill(struct inet_frag_queue *q, int *refs);

diff --git a/include/net/ipv6_frag.h b/include/net/ipv6_frag.h
index 38ef66826939ee561e409f528292ca4af1e29a3b..41d9fc6965f9a0cd5b624b6f400c7f27a538913b 100644 (file)
--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h
@@ -69,9 +69,6 @@ ip6frag_expire_frag_queue(struct net *net, struct frag_queue *fq)
        int refs = 1;
 
        rcu_read_lock();
-       /* Paired with the WRITE_ONCE() in fqdir_pre_exit(). */
-       if (READ_ONCE(fq->q.fqdir->dead))
-               goto out_rcu_unlock;
        spin_lock(&fq->q.lock);
 
        if (fq->q.flags & INET_FRAG_COMPLETE)
@@ -80,6 +77,12 @@ ip6frag_expire_frag_queue(struct net *net, struct frag_queue *fq)
        fq->q.flags |= INET_FRAG_DROP;
        inet_frag_kill(&fq->q, &refs);
 
+       /* Paired with the WRITE_ONCE() in fqdir_pre_exit(). */
+       if (READ_ONCE(fq->q.fqdir->dead)) {
+               inet_frag_queue_flush(&fq->q, 0);
+               goto out;
+       }
+
        dev = dev_get_by_index_rcu(net, fq->iif);
        if (!dev)
                goto out;

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 1bf969b5a1cb5570e0bb7ed64600c51cb3695463..001ee5c4d962e3adce85e231760583ef9331b830 100644 (file)
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -218,6 +218,41 @@ static int __init inet_frag_wq_init(void)
 
 pure_initcall(inet_frag_wq_init);
 
+void fqdir_pre_exit(struct fqdir *fqdir)
+{
+       struct inet_frag_queue *fq;
+       struct rhashtable_iter hti;
+
+       /* Prevent creation of new frags.
+        * Pairs with READ_ONCE() in inet_frag_find().
+        */
+       WRITE_ONCE(fqdir->high_thresh, 0);
+
+       /* Pairs with READ_ONCE() in inet_frag_kill(), ip_expire()
+        * and ip6frag_expire_frag_queue().
+        */
+       WRITE_ONCE(fqdir->dead, true);
+
+       rhashtable_walk_enter(&fqdir->rhashtable, &hti);
+       rhashtable_walk_start(&hti);
+
+       while ((fq = rhashtable_walk_next(&hti))) {
+               if (IS_ERR(fq)) {
+                       if (PTR_ERR(fq) != -EAGAIN)
+                               break;
+                       continue;
+               }
+               spin_lock_bh(&fq->lock);
+               if (!(fq->flags & INET_FRAG_COMPLETE))
+                       inet_frag_queue_flush(fq, 0);
+               spin_unlock_bh(&fq->lock);
+       }
+
+       rhashtable_walk_stop(&hti);
+       rhashtable_walk_exit(&hti);
+}
+EXPORT_SYMBOL(fqdir_pre_exit);
+
 void fqdir_exit(struct fqdir *fqdir)
 {
        INIT_WORK(&fqdir->destroy_work, fqdir_work_fn);
@@ -290,6 +325,7 @@ void inet_frag_queue_flush(struct inet_frag_queue *q,
 {
        unsigned int sum;
 
+       reason = reason ?: SKB_DROP_REASON_FRAG_REASM_TIMEOUT;
        sum = inet_frag_rbtree_purge(&q->rb_fragments, reason);
        sub_frag_mem_limit(q->fqdir, sum);
 }

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 32f1c1a46ba72b66b526500c7b235444c2b4e4a4..56b0f738d2f27b6b4c4b55f5ca9368305ce1eb4f 100644 (file)
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -134,11 +134,6 @@ static void ip_expire(struct timer_list *t)
        net = qp->q.fqdir->net;
 
        rcu_read_lock();
-
-       /* Paired with WRITE_ONCE() in fqdir_pre_exit(). */
-       if (READ_ONCE(qp->q.fqdir->dead))
-               goto out_rcu_unlock;
-
        spin_lock(&qp->q.lock);
 
        if (qp->q.flags & INET_FRAG_COMPLETE)
@@ -146,6 +141,13 @@ static void ip_expire(struct timer_list *t)
 
        qp->q.flags |= INET_FRAG_DROP;
        inet_frag_kill(&qp->q, &refs);
+
+       /* Paired with WRITE_ONCE() in fqdir_pre_exit(). */
+       if (READ_ONCE(qp->q.fqdir->dead)) {
+               inet_frag_queue_flush(&qp->q, 0);
+               goto out;
+       }
+
        __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
        __IP_INC_STATS(net, IPSTATS_MIB_REASMTIMEOUT);