[PATCH v4] tracing: Fix out of bounds write in get_trace_buf

[Qiujun Huang]

The subscript should be nesting - 1, as nesting had self-added.

Fixes: 3d9622c12c887 ("tracing: Add barrier to trace_printk() buffer nesting 
modification")
Signed-off-by: Qiujun Huang <hqjag...@gmail.com>
---
v4:
Find the right patch which cause the problem.
v3:
Modify the way of array reference instead.
v2:
Fix a typo in the title.
---
 kernel/trace/trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 528971714fc6..daa96215e294 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3132,7 +3132,7 @@ static char *get_trace_buf(void)
 
        /* Interrupts must see nesting incremented before we use the buffer */
        barrier();
-       return &buffer->buffer[buffer->nesting][0];
+       return &buffer->buffer[buffer->nesting - 1][0];
 }
 
 static void put_trace_buf(void)
-- 
2.17.1