Re: [PATCH] tracing: Replace deprecated strncpy() with memcpy() for stack_trace_filter_buf

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2025-04-04 08:28, Devaansh Kumar wrote:
> On Fri, 4 Apr 2025 at 01:05, Steven Rostedt <rostedt@goodmis.org> wrote:
>>
>> On Fri,  4 Apr 2025 00:43:40 +0530
>> Devaansh Kumar <devaanshk840@gmail.com> wrote:
>>
>>> @@ -537,14 +538,16 @@ stack_trace_sysctl(struct ctl_table *table, int write, void *buffer,
>>>        return ret;
>>>   }
>>>
>>> -static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
>>> +static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata __nonstring;
>>>
>>>   static __init int enable_stacktrace(char *str)
>>>   {
>>>        int len;
>>>
>>> -     if ((len = str_has_prefix(str, "_filter=")))
>>> -             strncpy(stack_trace_filter_buf, str + len, COMMAND_LINE_SIZE);
>>> +     len = str_has_prefix(str, "_filter=");
>>> +
>>> +     if (len)
>>> +             memcpy(stack_trace_filter_buf, str + len, sizeof(stack_trace_filter_buf));
>>
>> Hmm, this location looks like it can just use strscpy().
> 
> Yes strscpy() also works. But since stack_trace_filter_buf is length
> bounded, shouldn't memcpy be the right choice?

It's not only about the destination, but also about the source length.

AFAIU, turning a strncpy into a memcpy here will overflow reading the
input @str if the input string is smaller than
sizeof(stack_trace_filter_buf) + len.

This can trigger page faults or make KASAN unhappy.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com