From 7c4a5b89a0b5a57a64b601775b296abf77a9fe97 Mon Sep 17 00:00:00 2001
From: Pietro Borrello <borrello@diag.uniroma1.it>
Date: Mon, 6 Feb 2023 22:33:54 +0000
Subject: [PATCH] sched/rt: pick_next_rt_entity(): check list_entry
Git-commit: 7c4a5b89a0b5a57a64b601775b296abf77a9fe97
Patch-mainline: v6.3-rc1
References: bsc#1208600 CVE-2023-1077
Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
removed any path which could make pick_next_rt_entity() return NULL.
However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
pick_next_rt_entity()) still checks the error condition, which can
never happen, since list_entry() never returns NULL.
Remove the BUG_ON check, and instead emit a warning in the only
possible error condition here: the queue being empty which should
never happen.
Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v3-1-b1a71bd1ac6b@diag.uniroma1.it
Signed-off-by: Frederic Weisbecker <fweisbecker@suse.com>
---
kernel/sched/rt.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1491,6 +1491,10 @@ static struct sched_rt_entity *pick_next
BUG_ON(idx >= MAX_RT_PRIO);
queue = array->queue + idx;
+#ifdef CONFIG_SCHED_DEBUG
+ if (WARN_ON_ONCE(list_empty(queue)))
+ return NULL;
+#endif
next = list_entry(queue->next, struct sched_rt_entity, run_list);
return next;
@@ -1504,7 +1508,8 @@ static struct task_struct *_pick_next_ta
do {
rt_se = pick_next_rt_entity(rq, rt_rq);
- BUG_ON(!rt_se);
+ if (unlikely(!rt_se))
+ return NULL;
rt_rq = group_rt_rq(rt_se);
} while (rt_rq);