Re: [PATCH v4] tracing: Replace deprecated strncpy() with strscpy() for stack_trace_filter_buf

Steven Rostedt
2025-04-19T02:46:01Z

On Sat, 19 Apr 2025 03:44:41 +0530
Devaansh Kumar <devaanshk840@gmail.com> wrote:

> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index 14c6f272c4d8..0f2253f3bc8c 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -542,7 +542,7 @@ 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);
> + strscpy(stack_trace_filter_buf, str + len, sizeof(stack_trace_filter_buf));

Is the sizeof() needed?

From include/linux/string.h:

/**
* strscpy - Copy a C-string into a sized buffer
* @dst: Where to copy the string to
* @src: Where to copy the string from
* @...: Size of destination buffer (optional)
*
* Copy the source string @src, or as much of it as fits, into the
* destination @dst buffer. The behavior is undefined if the string
* buffers overlap. The destination @dst buffer is always NUL terminated,
* unless it's zero-sized.
*
* The size argument @... is only required when @dst is not an array, or
* when the copy needs to be smaller than sizeof(@dst).
*
* Preferred to strncpy() since it always returns a valid string, and
* doesn't unnecessarily force the tail of the destination buffer to be
* zero padded. If padding is desired please use strscpy_pad().
*
* Returns the number of characters copied in @dst (not including the
* trailing %NUL) or -E2BIG if @size is 0 or the copy from @src was
* truncated.
*/
#define strscpy(dst, src, ...) \
CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)

With stack_trace_filter_buf defined as:

static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;

This looks like a text book example of just having that be:

strscpy(stack_trace_filter_buf, str + len);

-- Steve

>
> stack_tracer_enabled = 1;
> return 1;