linux-kernel - Re: [PATCHv2] mm: do not export const kfree and kstrdup variants

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <67060a27-5830-4ea1-955f-722f1d2c83b4@wanadoo.fr>
Date: Tue, 24 Sep 2024 21:45:59 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Christoph Hellwig <hch@...radead.org>,
 Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Andrey Skvortsov <andrej.skvortzov@...il.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] mm: do not export const kfree and kstrdup variants

Le 24/09/2024 à 09:02, Christoph Hellwig a écrit :
> On Tue, Sep 24, 2024 at 03:56:53PM +0900, Sergey Senozhatsky wrote:
>> Totally agree with all the points, I haven't looked at how
>> popular that API was before sending out the patch.  Is there
>> some sort of "built time const" but for strings that we, perhaps,
>> can add to kfree_const() (and make kfree_const() always inline)?
>> So that we can turn this
>>
>> 	str = "boom";
>> 	...
>> 	kfree_const(str);
>>
>> into a safe scenario for modules.
> 
> Not sure, but even then the API would be horrible as it still would
> not work for constants in other modules than the one calling it.
> 
> 

So, the best is to audit, at least code that can be built as a module 
for str = "boom" pattern, and fix relevant places?


Or, considering that these these _const() versions are only there to 
save a few bytes of memory, wonder if it really worth it?

In other word:
	1) apply something like the patch below
	2) remove the API


At a minimum, I think that devm_kstrdup_const() could be removed.

CJ


diff --git a/mm/util.c b/mm/util.c
index 4f1275023eb7..fd5e98fb6362 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -39,8 +39,7 @@
   */
  void kfree_const(const void *x)
  {
-       if (!is_kernel_rodata((unsigned long)x))
-               kfree(x);
+       kfree(x);
  }
  EXPORT_SYMBOL(kfree_const);

@@ -81,9 +80,6 @@ EXPORT_SYMBOL(kstrdup);
   */
  const char *kstrdup_const(const char *s, gfp_t gfp)
  {
-       if (is_kernel_rodata((unsigned long)s))
-               return s;
-
         return kstrdup(s, gfp);
  }
  EXPORT_SYMBOL(kstrdup_const);