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]>
---
Changes since v1:
- Print partial line to show the broken trace event when overflowed print_trace_line
kernel/trace/trace.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 47a44b055a1d..81c36dc80212 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6786,7 +6786,32 @@ 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 trace_line of the tracer overflows seq_file
+ * buffer, trace_seq_to_user returns -EBUSY.
+ * In this case, we need to consume, otherwise,
+ * while loop will peek this event next time,
+ * resulting in an infinite loop.
+ */
+ if (trace_seq_has_overflowed(&iter->seq)) {
+ /*
+ * Print the partial line,
+ * that way we can see the broken trace event.
+ */
+ char dots[] = "...\n";
+
+ iter->seq.full = 0;
+ if (seq_buf_buffer_left(&iter->seq.seq) < strlen(dots)) {
+ iter->seq.seq.len =
+ seq_buf_used(&iter->seq.seq) - strlen(dots);
+ }
+ trace_seq_puts(&iter->seq, dots);
+
+ trace_consume(iter);
+ break;
+ }
+
+ /* In other cases, don't print partial lines */
iter->seq.seq.len = save_len;
break;
}
--
2.30.GIT
On Fri, 18 Nov 2022 18:25:21 +0800
Yang Jihong <[email protected]> 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]>
> ---
>
> Changes since v1:
> - Print partial line to show the broken trace event when overflowed print_trace_line
>
> kernel/trace/trace.c | 27 ++++++++++++++++++++++++++-
> 1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 47a44b055a1d..81c36dc80212 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6786,7 +6786,32 @@ 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 trace_line of the tracer overflows seq_file
> + * buffer, trace_seq_to_user returns -EBUSY.
> + * In this case, we need to consume, otherwise,
> + * while loop will peek this event next time,
> + * resulting in an infinite loop.
> + */
> + if (trace_seq_has_overflowed(&iter->seq)) {
We need to only do this if save_len is zero. Because the reason that it
returns TRACE_TYPE_PARTIAL_LINE is usually because it overflowed.
This loops until the trace_seq is full, so it's OK to have it overflow.
The case I believe you are fixing, is the case were one
print_trace_line() actually fills the entire trace_seq in one shot. In
which case, it will never print, and in that case, save_len will be zero.
-- Steve
> + /*
> + * Print the partial line,
> + * that way we can see the broken trace event.
> + */
> + char dots[] = "...\n";
> +
> + iter->seq.full = 0;
> + if (seq_buf_buffer_left(&iter->seq.seq) < strlen(dots)) {
> + iter->seq.seq.len =
> + seq_buf_used(&iter->seq.seq) - strlen(dots);
> + }
> + trace_seq_puts(&iter->seq, dots);
> +
> + trace_consume(iter);
> + break;
> + }
> +
> + /* In other cases, don't print partial lines */
> iter->seq.seq.len = save_len;
> break;
> }
Hello,
On 2022/11/21 3:38, Steven Rostedt wrote:
> On Fri, 18 Nov 2022 18:25:21 +0800
> Yang Jihong <[email protected]> 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]>
>> ---
>>
>> Changes since v1:
>> - Print partial line to show the broken trace event when overflowed print_trace_line
>>
>> kernel/trace/trace.c | 27 ++++++++++++++++++++++++++-
>> 1 file changed, 26 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 47a44b055a1d..81c36dc80212 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -6786,7 +6786,32 @@ 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 trace_line of the tracer overflows seq_file
>> + * buffer, trace_seq_to_user returns -EBUSY.
>> + * In this case, we need to consume, otherwise,
>> + * while loop will peek this event next time,
>> + * resulting in an infinite loop.
>> + */
>> + if (trace_seq_has_overflowed(&iter->seq)) {
>
> We need to only do this if save_len is zero. Because the reason that it
> returns TRACE_TYPE_PARTIAL_LINE is usually because it overflowed.
>
> This loops until the trace_seq is full, so it's OK to have it overflow.
> The case I believe you are fixing, is the case were one
> print_trace_line() actually fills the entire trace_seq in one shot. In
> which case, it will never print, and in that case, save_len will be zero.
>
Yes, I'm fixing the situation you mentioned.
For the sake of discussion, I've replied in the v1 patch to see if it's
just add "trace_seq_puts(&iter->seq, "[LINE TOO BIG]\n");" or a more
complex situation.
Thanks,
Yang