linux-kernel - [PATCH linux-next] printk: nbcon: Fix nbcon_cpu_emergency

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date: Wed, 05 Jun 2024 11:57:34 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
    Steven Rostedt <rostedt@...dmis.org>,
    Juri Lelli <juri.lelli@...hat.com>,
    linux-kernel@...r.kernel.org
Subject: [PATCH linux-next] printk: nbcon: Fix nbcon_cpu_emergency_flush()
 when preemptible

nbcon_cpu_emergency_flush() can be called in a preemptible
context. In that case the CPU is not in an emergency state.
However, in order to see that the CPU is not in an emergency
state (accessing the per-cpu variable), preemption must be
disabled.

Disable preemption when checking the CPU state.

Reported-by: Juri Lelli <juri.lelli@...hat.com>
Closes: https://lore.kernel.org/aqkcpca4vgadxc3yzcu74xwq3grslj5m43f3eb5fcs23yo2gy4@gcsnqcts5tos
Fixes: 46a1379208b7 ("printk: nbcon: Implement emergency sections")
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/nbcon.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 19f0db6945e4..39eb369880d9 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1443,8 +1443,19 @@ void nbcon_cpu_emergency_exit(void)
  */
 void nbcon_cpu_emergency_flush(void)
 {
+	bool is_emergency;
+
+	/*
+	 * If this context is not an emergency context, preemption might be
+	 * enabled. To be sure, disable preemption when checking if this is
+	 * an emergency context.
+	 */
+	preempt_disable();
+	is_emergency = (*nbcon_get_cpu_emergency_nesting() != 0);
+	preempt_enable();
+
 	/* The explicit flush is needed only in the emergency context. */
-	if (*(nbcon_get_cpu_emergency_nesting()) == 0)
+	if (!is_emergency)
 		return;
 
 	nbcon_atomic_flush_pending();
-- 
2.30.2