linux-kernel - [PATCH kernel] srcu: Fix static initialization

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Date:   Wed,  9 Sep 2020 00:43:06 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     rcu@...r.kernel.org
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH kernel] srcu: Fix static initialization

init_srcu_struct_nodes() is called with is_static==true only internally
and when this happens, the srcu->sda is not initialized in
init_srcu_struct_fields() and we crash on dereferencing @sdp.

This fixes the crash by moving "if (is_static)" out of the loop which
only does useful work for is_static=false case anyway.

Found by syzkaller.

Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
---
 kernel/rcu/srcutree.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index c100acf332ed..49b54a50bde8 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -135,6 +135,9 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
 				   levelspread[level - 1];
 	}
 
+	if (is_static)
+		return;
+
 	/*
 	 * Initialize the per-CPU srcu_data array, which feeds into the
 	 * leaves of the srcu_node tree.
@@ -161,8 +164,6 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
 		timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
 		sdp->ssp = ssp;
 		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
-		if (is_static)
-			continue;
 
 		/* Dynamically allocated, better be no srcu_read_locks()! */
 		for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) {
-- 
2.17.1