Merge branch 'inet-add-drop-monitor-support'

Eric Dumazet says:

====================
inet: add drop monitor support

I recently tried to analyse flakes in ip_defrag selftest.
This failed miserably.

IPv4 and IPv6 reassembly units are causing false kfree_skb()
notifications. It is time to deal with this issue.

First two patches are changing core networking to better
deal with eventual skb frag_list chains, in respect
of kfree_skb/consume_skb status.

Last three patches are adding three new drop reasons,
and make sure skbs that have been reassembled into
a large datagram are no longer viewed as dropped ones.

After this, understanding why ip_defrag selftest is flaky
is possible using standard drop monitoring tools.
====================

Link: https://lore.kernel.org/r/20221029154520.2747444-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 21 insertions, 2 deletions

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index c1cbcdbaf149..70539288f995 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -68,6 +68,9 @@
 	FN(IP_INADDRERRORS)		\
 	FN(IP_INNOROUTES)		\
 	FN(PKT_TOO_BIG)			\
+	FN(DUP_FRAG)			\
+	FN(FRAG_REASM_TIMEOUT)		\
+	FN(FRAG_TOO_FAR)		\
 	FNe(MAX)
 
 /**
@@ -80,6 +83,8 @@ enum skb_drop_reason {
 	 * @SKB_NOT_DROPPED_YET: skb is not dropped yet (used for no-drop case)
 	 */
 	SKB_NOT_DROPPED_YET = 0,
+	/** @SKB_CONSUMED: packet has been consumed */
+	SKB_CONSUMED,
 	/** @SKB_DROP_REASON_NOT_SPECIFIED: drop reason is not specified */
 	SKB_DROP_REASON_NOT_SPECIFIED,
 	/** @SKB_DROP_REASON_NO_SOCKET: socket not found */
@@ -298,6 +303,15 @@ enum skb_drop_reason {
 	 * MTU)
 	 */
 	SKB_DROP_REASON_PKT_TOO_BIG,
+	/** @SKB_DROP_REASON_DUP_FRAG: duplicate fragment */
+	SKB_DROP_REASON_DUP_FRAG,
+	/** @SKB_DROP_REASON_FRAG_REASM_TIMEOUT: fragment reassembly timeout */
+	SKB_DROP_REASON_FRAG_REASM_TIMEOUT,
+	/**
+	 * @SKB_DROP_REASON_FRAG_TOO_FAR: ipv4 fragment too far.
+	 * (/proc/sys/net/ipv4/ipfrag_max_dist)
+	 */
+	SKB_DROP_REASON_FRAG_TOO_FAR,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
 	 * used as a real 'reason'
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 0b0876610553..b23ddec3cd5c 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -7,6 +7,7 @@
 #include <linux/in6.h>
 #include <linux/rbtree_types.h>
 #include <linux/refcount.h>
+#include <net/dropreason.h>
 
 /* Per netns frag queues directory */
 struct fqdir {
@@ -34,12 +35,14 @@ struct fqdir {
  * @INET_FRAG_LAST_IN: final fragment has arrived
  * @INET_FRAG_COMPLETE: frag queue has been processed and is due for destruction
  * @INET_FRAG_HASH_DEAD: inet_frag_kill() has not removed fq from rhashtable
+ * @INET_FRAG_DROP: if skbs must be dropped (instead of being consumed)
  */
 enum {
 	INET_FRAG_FIRST_IN	= BIT(0),
 	INET_FRAG_LAST_IN	= BIT(1),
 	INET_FRAG_COMPLETE	= BIT(2),
 	INET_FRAG_HASH_DEAD	= BIT(3),
+	INET_FRAG_DROP		= BIT(4),
 };
 
 struct frag_v4_compare_key {
@@ -139,7 +142,8 @@ void inet_frag_destroy(struct inet_frag_queue *q);
 struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key);
 
 /* Free all skbs in the queue; return the sum of their truesizes. */
-unsigned int inet_frag_rbtree_purge(struct rb_root *root);
+unsigned int inet_frag_rbtree_purge(struct rb_root *root,
+				    enum skb_drop_reason reason);
 
 static inline void inet_frag_put(struct inet_frag_queue *q)
 {
diff --git a/include/net/ipv6_frag.h b/include/net/ipv6_frag.h
index 5052c66e22d2..7321ffe3a108 100644
--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h
@@ -76,6 +76,7 @@ ip6frag_expire_frag_queue(struct net *net, struct frag_queue *fq)
 	if (fq->q.flags & INET_FRAG_COMPLETE)
 		goto out;
 
+	fq->q.flags |= INET_FRAG_DROP;
 	inet_frag_kill(&fq->q);
 
 	dev = dev_get_by_index_rcu(net, fq->iif);
@@ -101,7 +102,7 @@ ip6frag_expire_frag_queue(struct net *net, struct frag_queue *fq)
 	spin_unlock(&fq->q.lock);
 
 	icmpv6_send(head, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME, 0);
-	kfree_skb(head);
+	kfree_skb_reason(head, SKB_DROP_REASON_FRAG_REASM_TIMEOUT);
 	goto out_rcu_unlock;
 
 out: