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From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH 5/7] eval_map_next should increase position index
To:     linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        NeilBrown <neilb@suse.com>, Waiman Long <longman@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Oberparleiter <oberpar@linux.ibm.com>
Message-ID: <7ad85b22-1866-977c-db17-88ac438bc764@virtuozzo.com>
Date:   Fri, 24 Jan 2020 10:03:01 +0300
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if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 kernel/trace/trace.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ddb7e7f..a337764 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5361,14 +5361,12 @@ static void *eval_map_next(struct seq_file *m, void *v, loff_t *pos)
 	 * Paranoid! If ptr points to end, we don't want to increment past it.
 	 * This really should never happen.
 	 */
+	(*pos)++;
 	ptr = update_eval_map(ptr);
 	if (WARN_ON_ONCE(!ptr))
 		return NULL;
 
 	ptr++;
-
-	(*pos)++;
-
 	ptr = update_eval_map(ptr);
 
 	return ptr;
-- 
1.8.3.1