linux-kernel - [PATCH] printk: Fix seq check inside devkmsg

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Message-ID: <1642505688-1194-1-git-send-email-quic_mojha@quicinc.com>
Date:   Tue, 18 Jan 2022 17:04:48 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <john.ogness@...utronix.de>, <rostedt@...dmis.org>,
        <senozhatsky@...omium.org>, <pmladek@...e.com>,
        Mukesh Ojha <quic_mojha@...cinc.com>
Subject: [PATCH] printk: Fix seq check inside devkmsg_read()

prb_read_valid() could return a record whose seq number can be
newer than the requested one. In that case, we allow the reading
of the data instead of erroring out.

This commit fixes this by correcting the check.

Fixes: ce6de43a547b6e01a3 ("printk: avoid prb_first_valid_seq() where possible")
Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
---
 kernel/printk/printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 155229f..53b09b98 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -738,7 +738,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 			goto out;
 	}
 
-	if (r->info->seq != atomic64_read(&user->seq)) {
+	if (r->info->seq < atomic64_read(&user->seq)) {
 		/* our last seen message is gone, return error and reset */
 		atomic64_set(&user->seq, r->info->seq);
 		ret = -EPIPE;
-- 
2.7.4