[PATCH 6.1 1044/1191] net: kcm: Hold RCU read lock while running BPF parser

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Junseo Lim <redacted>

[ Upstream commit b0346dd64e4905291cc9c479f2e6cf1884ced4e6 ]

kcm_parse_func_strparser() calls bpf_prog_run_pin_on_cpu() which
prevents CPU migration, but does not establish an RCU read-side
critical section. Consequently, BPF map operations can trigger
WARN_ON_ONCE(!bpf_rcu_lock_held()) when called from the KCM strparser
program.

Hold the RCU read lock while running the program.

Fixes: 9b73896a81dc ("kcm: Use stream parser")
Reported-by: Sechang Lim <redacted>
Signed-off-by: Junseo Lim <redacted>
Link: https://patch.msgid.link/20260813035136.106167-1-zirajs7@gmail.com (local)
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/kcm/kcmsock.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index ba221c6a8cbd7..ab7629cee1bd0 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c

@@ -5,6 +5,7 @@
  * Copyright (c) 2016 Tom Herbert <tom@herbertland.com>
  */
 
+#include <linux/rcupdate.h>
 #include <linux/bpf.h>
 #include <linux/errno.h>
 #include <linux/errqueue.h>

@@ -386,7 +387,9 @@ static int kcm_parse_func_strparser(struct strparser *strp, struct sk_buff *skb)
 	struct bpf_prog *prog = psock->bpf_prog;
 	int res;
 
+	rcu_read_lock();
 	res = bpf_prog_run_pin_on_cpu(prog, skb);
+	rcu_read_unlock();
 	return res;
 }
 

-- 
2.53.0