2022-11-29 12:02:55

by Yang Jihong

Subject: [PATCH v4] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

print_trace_line may overflow seq_file buffer. If the event is not
consumed, the while loop keeps peeking this event, causing a infinite loop.

Signed-off-by: Yang Jihong <[email protected]>
---
kernel/trace/trace.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a7fe0e115272..de7c99f4b539 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6787,7 +6787,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,

ret = print_trace_line(iter);
if (ret == TRACE_TYPE_PARTIAL_LINE) {
- /* don't print partial lines */
+ /*
+ * If one print_trace_line() fills entire trace_seq in one shot,
+ * trace_seq_to_user() will returns -EBUSY because save_len == 0,
+ * In this case, we need to consume it, otherwise, loop will peek
+ * this event next time, resulting in an infinite loop.
+ */
+ if (save_len == 0) {
+ iter->seq.full = 0;
+ trace_seq_puts(&iter->seq, "[LINE TOO BIG]\n");
+ trace_consume(iter);
+ break;
+ }
+
+ /* In other cases, don't print partial lines */
iter->seq.seq.len = save_len;
break;
}
--
2.30.GIT

2022-12-12 03:26:22

by Yang Jihong

Subject: Re: [PATCH v4] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

Hello,

PING.

Are there any other problems with this patch?

Thanks,
Yang.

On 2022/11/29 19:30, Yang Jihong wrote:
> print_trace_line may overflow seq_file buffer. If the event is not
> consumed, the while loop keeps peeking this event, causing a infinite loop.
>
> Signed-off-by: Yang Jihong <[email protected]>
> ---
> kernel/trace/trace.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a7fe0e115272..de7c99f4b539 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6787,7 +6787,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
>
> ret = print_trace_line(iter);
> if (ret == TRACE_TYPE_PARTIAL_LINE) {
> - /* don't print partial lines */
> + /*
> + * If one print_trace_line() fills entire trace_seq in one shot,
> + * trace_seq_to_user() will returns -EBUSY because save_len == 0,
> + * In this case, we need to consume it, otherwise, loop will peek
> + * this event next time, resulting in an infinite loop.
> + */
> + if (save_len == 0) {
> + iter->seq.full = 0;
> + trace_seq_puts(&iter->seq, "[LINE TOO BIG]\n");
> + trace_consume(iter);
> + break;
> + }
> +
> + /* In other cases, don't print partial lines */
> iter->seq.seq.len = save_len;
> break;
> }
>

2022-12-12 15:58:39

by Steven Rostedt

Subject: Re: [PATCH v4] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

On Mon, 12 Dec 2022 10:57:08 +0800
Yang Jihong <[email protected]> wrote:

> Hello,
>
> PING.
>
> Are there any other problems with this patch?

Thanks for the ping, I'll take a look at it. It somehow got lost in the
noise of other patches :-/

-- Steve