linux-kernel - [PATCH v2 7/7] kallsyms: Prevent module removal when printing module name and buildid

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Message-ID: <20251112142003.182062-8-pmladek@suse.com>
Date: Wed, 12 Nov 2025 15:20:03 +0100
From: Petr Mladek <pmladek@...e.com>
To: Petr Pavlu <petr.pavlu@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <kees@...nel.org>
Cc: Aaron Tomlin <atomlin@...mlin.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Daniel Gomez <da.gomez@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-modules@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 7/7] 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().

Reviewed-by: Aaron Tomlin <atomlin@...mlin.com>
Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/kallsyms.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 5bc1646f8639..202d39f5493a 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -471,6 +471,9 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 	unsigned long offset, size;
 	int len;
 
+	/* Prevent module removal until modname and modbuildid are printed */
+	guard(rcu)();
+
 	address += symbol_offset;
 	len = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
 				       buffer);
-- 
2.51.1