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

[Mathieu Desnoyers]

On 2025-04-04 08:28, Devaansh Kumar wrote:

On Fri, 4 Apr 2025 at 01:05, Steven Rostedt <rost...@goodmis.org> wrote:

On Fri,  4 Apr 2025 00:43:40 +0530
Devaansh Kumar <devaanshk...@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