From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Jeff Layton <jlayton@kernel.org>,
	Chuck Lever <cel@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15.y] sunrpc: defer rq_argp and rq_resp free until after RCU grace period
Date: Tue,  8 Sep 2026 21:47:28 -0400
Message-ID: <20260909014728.928965-1-sashal@kernel.org>
In-Reply-To: <2026090350-lip-cognitive-6180@gregkh>
References: <2026090350-lip-cognitive-6180@gregkh>
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From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit c479bde671cbe2f9e152834a8b0eb7c3c295bbaf ]

svc_rqst_free() frees rqstp->rq_argp and rqstp->rq_resp synchronously
via kfree(), but defers the rqstp struct free via kfree_rcu().  After
svc_exit_thread() calls list_del_rcu() and svc_rqst_free(), there is
a window where RCU readers that started before list_del_rcu() can still
traverse the thread list and find the rqstp.  These readers (e.g.
nfsd_nl_rpc_status_get_dumpit()) dereference rqstp->rq_argp, which has
already been freed — a use-after-free.

Fix this by moving the kfree of rq_argp and rq_resp into an explicit
call_rcu() callback alongside the struct free.  Resources not accessed
by RCU readers (bvec, buffer pages, scratch folio, auth_data) remain
synchronously freed.

Fixes: 812443865c5f ("sunrpc: add a rcu_head to svc_rqst and use kfree_rcu to free it")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260611-nfsd-testing-v2-4-5b90e276f2d9@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
[ adjusted context around svc_rqst_free() to match the older exported function with page-based cleanup. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sunrpc/svc.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 92d88aac2adff..06ed7bfe11620 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -841,6 +841,15 @@ void svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
 }
 EXPORT_SYMBOL_GPL(svc_rqst_replace_page);
 
+static void svc_rqst_free_rcu(struct rcu_head *head)
+{
+	struct svc_rqst *rqstp = container_of(head, struct svc_rqst, rq_rcu_head);
+
+	kfree(rqstp->rq_resp);
+	kfree(rqstp->rq_argp);
+	kfree(rqstp);
+}
+
 /*
  * Called from a server thread as it's exiting. Caller must hold the "service
  * mutex" for the service.
@@ -851,10 +860,8 @@ svc_rqst_free(struct svc_rqst *rqstp)
 	svc_release_buffer(rqstp);
 	if (rqstp->rq_scratch_page)
 		put_page(rqstp->rq_scratch_page);
-	kfree(rqstp->rq_resp);
-	kfree(rqstp->rq_argp);
 	kfree(rqstp->rq_auth_data);
-	kfree_rcu(rqstp, rq_rcu_head);
+	call_rcu(&rqstp->rq_rcu_head, svc_rqst_free_rcu);
 }
 EXPORT_SYMBOL_GPL(svc_rqst_free);
 
-- 
2.53.0