linux-kernel - [PATCH 4.1 46/65] livepatch: add module locking around kallsyms calls

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Date:	Sun, 19 Jul 2015 12:08:05 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Miroslav Benes <mbenes@...e.cz>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH 4.1 46/65] livepatch: add module locking around kallsyms calls

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miroslav Benes <mbenes@...e.cz>

commit 9a1bd63cdae4b623494c4ebaf723a91c35ec49fb upstream.

The list of loaded modules is walked through in
module_kallsyms_on_each_symbol (called by kallsyms_on_each_symbol). The
module_mutex lock should be acquired to prevent potential corruptions
in the list.

This was uncovered with new lockdep asserts in module code introduced by
the commit 0be964be0d45 ("module: Sanitize RCU usage and locking") in
recent next- trees.

Signed-off-by: Miroslav Benes <mbenes@...e.cz>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/livepatch/core.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -179,7 +179,9 @@ static int klp_find_object_symbol(const
 		.count = 0
 	};
 
+	mutex_lock(&module_mutex);
 	kallsyms_on_each_symbol(klp_find_callback, &args);
+	mutex_unlock(&module_mutex);
 
 	if (args.count == 0)
 		pr_err("symbol '%s' not found in symbol table\n", name);
@@ -219,13 +221,19 @@ static int klp_verify_vmlinux_symbol(con
 		.name = name,
 		.addr = addr,
 	};
+	int ret;
 
-	if (kallsyms_on_each_symbol(klp_verify_callback, &args))
-		return 0;
+	mutex_lock(&module_mutex);
+	ret = kallsyms_on_each_symbol(klp_verify_callback, &args);
+	mutex_unlock(&module_mutex);
+
+	if (!ret) {
+		pr_err("symbol '%s' not found at specified address 0x%016lx, kernel mismatch?\n",
+			name, addr);
+		return -EINVAL;
+	}
 
-	pr_err("symbol '%s' not found at specified address 0x%016lx, kernel mismatch?\n",
-		name, addr);
-	return -EINVAL;
+	return 0;
 }
 
 static int klp_find_verify_func_addr(struct klp_object *obj,


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