linux-kernel - [PATCH] tracing: Fix an off by one in _

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Date:   Wed, 20 Jun 2018 14:08:00 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: [PATCH] tracing: Fix an off by one in __next()

The > should be >= to prevent an off by one bug.

>From reviewing the code, it seems possible for
stack_trace_max.nr_entries to be set to .max_entries and in that case we
would be reading one element beyond the end of the stack_dump_trace[]
array.  If it's not set to .max_entries then the bug doesn't affect
runtime.

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 4237eba4ef20..6e3edd745c68 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -286,7 +286,7 @@ __next(struct seq_file *m, loff_t *pos)
 {
 	long n = *pos - 1;
 
-	if (n > stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX)
+	if (n >= stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX)
 		return NULL;
 
 	m->private = (void *)n;