From: Uladzislau Rezki (Sony) <urezki@gmail.com>
Date: Tue, 10 Jun 2025 17:34:48 +0000 (+0200)
Subject: rcu: Return early if callback is not specified
X-Git-Tag: v6.1.144~23
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=100040bff22c0c324073a73850670caf91bfe65b;p=thirdparty%2Fkernel%2Fstable.git

rcu: Return early if callback is not specified

[ Upstream commit 33b6a1f155d627f5bd80c7485c598ce45428f74f ]

Currently the call_rcu() API does not check whether a callback
pointer is NULL. If NULL is passed, rcu_core() will try to invoke
it, resulting in NULL pointer dereference and a kernel crash.

To prevent this and improve debuggability, this patch adds a check
for NULL and emits a kernel stack trace to help identify a faulty
caller.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index dd6e15ca63b0c..38ab28a53e108 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2827,6 +2827,10 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
 	/* Misaligned rcu_head! */
 	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
 
+	/* Avoid NULL dereference if callback is NULL. */
+	if (WARN_ON_ONCE(!func))
+		return;
+
 	if (debug_rcu_head_queue(head)) {
 		/*
 		 * Probable double call_rcu(), so leak the callback.