kallsyms: clean up modname and modbuildid initialization in kallsyms_lookup_buildid()

jira KERNEL-629
bugfix Fix sched_ext:select_cpu_dispatch_dbl_dsp selftest crash
commit-author Petr Mladek <pmladek@suse.com>
commit fda024f

The @modname and @modbuildid optional return parameters are set only when
the symbol is in a module.

Always initialize them so that they do not need to be cleared when the
module is not in a module.  It simplifies the logic and makes the code
even slightly more safe.

Note that bpf_address_lookup() function will get updated in a separate
patch.

Link: https://lkml.kernel.org/r/20251128135920.217303-3-pmladek@suse.com
	Signed-off-by: Petr Mladek <pmladek@suse.com>
	Cc: Aaron Tomlin <atomlin@atomlin.com>
	Cc: Alexei Starovoitov <ast@kernel.org>
	Cc: Daniel Borkman <daniel@iogearbox.net>
	Cc: Daniel Gomez <da.gomez@samsung.com>
	Cc: John Fastabend <john.fastabend@gmail.com>
	Cc: Kees Cook <kees@kernel.org>
	Cc: Luis Chamberalin <mcgrof@kernel.org>
	Cc: Marc Rutland <mark.rutland@arm.com>
	Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
	Cc: Petr Pavlu <petr.pavlu@suse.com>
	Cc: Sami Tolvanen <samitolvanen@google.com>
	Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
	Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit fda024f)
	Signed-off-by: Brett Mastbergen <bmastbergen@ciq.com>

Author: bmastbergen

kernel/kallsyms.c

@@ -357,6 +357,14 @@ static int kallsyms_lookup_buildid(unsigned long addr,
 
 	namebuf[KSYM_NAME_LEN - 1] = 0;
 	namebuf[0] = 0;
+	/*
+	 * Initialize the module-related return values. They are not set
+	 * when the symbol is in vmlinux or it is a bpf address.
+	 */
+	if (modname)
+		*modname = NULL;
+	if (modbuildid)
+		*modbuildid = NULL;
 
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
@@ -365,10 +373,6 @@ static int kallsyms_lookup_buildid(unsigned long addr,
 		/* Grab name */
 		kallsyms_expand_symbol(get_symbol_offset(pos),
 				       namebuf, KSYM_NAME_LEN);
-		if (modname)
-			*modname = NULL;
-		if (modbuildid)
-			*modbuildid = NULL;
 
 		return strlen(namebuf);
 	}