Patch "ipv6: sr: block BH in seg6_output_core() and seg6_input_core()" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ipv6: sr: block BH in seg6_output_core() and seg6_input_core()

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipv6-sr-block-bh-in-seg6_output_core-and-seg6_input_.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ef23b47ef3e6cce8ae8f8c9c9e61704257a37640
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Fri May 31 13:26:34 2024 +0000

    ipv6: sr: block BH in seg6_output_core() and seg6_input_core()
    
    [ Upstream commit c0b98ac1cc104f48763cdb27b1e9ac25fd81fc90 ]
    
    As explained in commit 1378817486d6 ("tipc: block BH
    before using dst_cache"), net/core/dst_cache.c
    helpers need to be called with BH disabled.
    
    Disabling preemption in seg6_output_core() is not good enough,
    because seg6_output_core() is called from process context,
    lwtunnel_output() only uses rcu_read_lock().
    
    We might be interrupted by a softirq, re-enter seg6_output_core()
    and corrupt dst_cache data structures.
    
    Fix the race by using local_bh_disable() instead of
    preempt_disable().
    
    Apply a similar change in seg6_input_core().
    
    Fixes: fa79581ea66c ("ipv6: sr: fix several BUGs when preemption is enabled")
    Fixes: 6c8702c60b88 ("ipv6: sr: add support for SRH encapsulation and injection with lwtunnels")
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: David Lebrun <dlebrun@xxxxxxxxxx>
    Acked-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240531132636.2637995-4-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
index 2e90672852c86..7dc447e08a486 100644
--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -313,9 +313,8 @@ static int seg6_input(struct sk_buff *skb)
 
 	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
 
-	preempt_disable();
+	local_bh_disable();
 	dst = dst_cache_get(&slwt->cache);
-	preempt_enable();
 
 	skb_dst_drop(skb);
 
@@ -323,14 +322,13 @@ static int seg6_input(struct sk_buff *skb)
 		ip6_route_input(skb);
 		dst = skb_dst(skb);
 		if (!dst->error) {
-			preempt_disable();
 			dst_cache_set_ip6(&slwt->cache, dst,
 					  &ipv6_hdr(skb)->saddr);
-			preempt_enable();
 		}
 	} else {
 		skb_dst_set(skb, dst);
 	}
+	local_bh_enable();
 
 	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
 	if (unlikely(err))
@@ -352,9 +350,9 @@ static int seg6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 
 	slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
 
-	preempt_disable();
+	local_bh_disable();
 	dst = dst_cache_get(&slwt->cache);
-	preempt_enable();
+	local_bh_enable();
 
 	if (unlikely(!dst)) {
 		struct ipv6hdr *hdr = ipv6_hdr(skb);
@@ -374,9 +372,9 @@ static int seg6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 			goto drop;
 		}
 
-		preempt_disable();
+		local_bh_disable();
 		dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
-		preempt_enable();
+		local_bh_enable();
 	}
 
 	skb_dst_drop(skb);