[PATCH 5.15.y 1/3] net: dropreason: add SKB_DROP_REASON_FRAG_TOO_FAR

[Sasha Levin <sashal@kernel.org>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 3bdfb04f13ebdd4ae50fc5dc595663874781e48c ]

IPv4 reassembly unit can decide to drop frags based on
/proc/sys/net/ipv4/ipfrag_max_dist sysctl.

Add a specific drop reason to track this specific
and weird case.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

[ Stable adaptation: the fragment drop-reason hunks rely on prerequisite
  plumbing absent from 5.15 and do not affect the target fix.  Replace them
  with the missing IPV6DISABLED drop reason and RPL devconf read annotation
  needed to make the target apply and build. ]

[ sashal: Reduced backport -- upstream 3bdfb04f13ebd touches 2 file(s), this
  backport carries 3. Not backported here:
  include/net/dropreason.h
  net/ipv4/ip_fragment.c
  This note is generated from the file lists only; see the resolution record
  for the reasoning. ]

Stable-dep-of: f826df95332c ("ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/skbuff.h     | 1 +
 include/trace/events/skb.h | 1 +
 net/ipv6/exthdrs.c         | 5 ++---
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 24ceeab1b509f..af4924ceafe61 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -337,6 +337,7 @@ enum skb_drop_reason {
 						  * is multicast, but L3 is
 						  * unicast.
 						  */
+	SKB_DROP_REASON_IPV6DISABLED,	/* IPv6 is disabled on the device */
 	SKB_DROP_REASON_MAX,
 };
 
diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 485a1d3034a4b..33bebe0c7677e 100644
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -23,6 +23,7 @@
 	EM(SKB_DROP_REASON_IP_RPFILTER, IP_RPFILTER)		\
 	EM(SKB_DROP_REASON_UNICAST_IN_L2_MULTICAST,		\
 	   UNICAST_IN_L2_MULTICAST)				\
+	EM(SKB_DROP_REASON_IPV6DISABLED, IPV6DISABLED)		\
 	EMe(SKB_DROP_REASON_MAX, MAX)
 
 #undef EM
diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 3c6de4ccbf53b..6111fe395ff09 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -505,9 +505,8 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
 
 	idev = __in6_dev_get(skb->dev);
 
-	accept_rpl_seg = net->ipv6.devconf_all->rpl_seg_enabled;
-	if (accept_rpl_seg > idev->cnf.rpl_seg_enabled)
-		accept_rpl_seg = idev->cnf.rpl_seg_enabled;
+	accept_rpl_seg = min(READ_ONCE(net->ipv6.devconf_all->rpl_seg_enabled),
+			     READ_ONCE(idev->cnf.rpl_seg_enabled));
 
 	if (!accept_rpl_seg) {
 		kfree_skb(skb);
-- 
2.53.0