linux-kernel - Re: module,sysfs: gpf in module_attr

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Date:	Tue, 23 Dec 2014 15:05:57 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Sasha Levin <sasha.levin@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>
Cc:	Kees Cook <keescook@...omium.org>
Subject: Re: module,sysfs: gpf in module_attr_store

Sasha Levin <sasha.levin@...cle.com> writes:
> Hi all,
>
> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel, I've stumbled on the following spew:

Nice catch!

Thanks for the report,
Rusty.

Subject: param: initialize store function to NULL if not available.

I rebased Kees' 'param: do not set store func without write perm'
on top of my 'params: cleanup sysfs allocation'.  However, my patch
uses krealloc which doesn't zero memory, leaving .store unset.

Reported-by: Sasha Levin <sasha.levin@...cle.com>
Cc: Kees Cook <keescook@...omium.org>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff --git a/kernel/params.c b/kernel/params.c
index 0af9b2c4e56c..bd65d136a470 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -648,6 +648,8 @@ static __modinit int add_sysfs_param(struct module_kobject *mk,
 	/* Do not allow runtime DAC changes to make param writable. */
 	if ((kp->perm & (S_IWUSR | S_IWGRP | S_IWOTH)) != 0)
 		mk->mp->attrs[mk->mp->num].mattr.store = param_attr_store;
+	else
+		mk->mp->attrs[mk->mp->num].mattr.store = NULL;
 	mk->mp->attrs[mk->mp->num].mattr.attr.name = (char *)name;
 	mk->mp->attrs[mk->mp->num].mattr.attr.mode = kp->perm;
 	mk->mp->num++;
--
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