[PATCH 6/6] kallsyms: Prevent module removal when printing module name and buildid

[Petr Mladek <pmladek@suse.com>]

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().

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/kallsyms.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index ff7017337535..1fda06b6638c 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -468,6 +468,9 @@ 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