kallsyms: prevent module removal when printing module name and buildid

kallsyms_lookup_buildid() copies the symbol name into the given buffer so
that it can be safely read anytime later. But it just copies pointers to
mod->name and mod->build_id which might get reused after the related
struct module gets removed.

The lifetime of struct module is synchronized using RCU. Take the rcu
read lock for the entire __sprint_symbol().

Link: https://lkml.kernel.org/r/20251128135920.217303-8-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: 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>