2020-10-29 16:21:26

by Qiujun Huang

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

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 <[email protected]>
---
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

2020-10-29 18:54:19

by Steven Rostedt

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

On Fri, 30 Oct 2020 00:19:05 +0800
Qiujun Huang <[email protected]> wrote:

> The subscript should be nesting - 1, as nesting had self-added.
>
> Fixes: 3d9622c12c887 ("tracing: Add barrier to trace_printk() buffer nesting modification")

Thanks, I'll still use the updated change log.

-- Steve

> Signed-off-by: Qiujun Huang <[email protected]>
> ---
> 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)