linux-kernel - Re: [PATCH V2] limit minixfs printks on corrupted dir i

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Date:	Thu, 09 Aug 2007 23:47:42 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Eric Sandeen <sandeen@...deen.net>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH V2] limit minixfs printks on corrupted dir i_size, CVE-2006-6058

Eric Sandeen <sandeen@...deen.net> wrote:

> This attempts to address CVE-2006-6058
> http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-6058
>  
> first reported at http://projects.info-pull.com/mokb/MOKB-17-11-2006.html
> 
> Essentially a corrupted minix dir inode reporting a very large
> i_size will loop for a very long time in minix_readdir, minix_find_entry,
> etc, because on EIO they just move on to try the next page.  This is
> under the BKL, printk-storming as well.  This can lock up the machine
> for a very long time.  Simply ratelimiting the printks gets things back
> under control.

> Index: linux-2.6.22-rc4/fs/minix/itree_v1.c
> ===================================================================
> --- linux-2.6.22-rc4.orig/fs/minix/itree_v1.c
> +++ linux-2.6.22-rc4/fs/minix/itree_v1.c
> @@ -27,7 +27,8 @@ static int block_to_path(struct inode *
>  if (block < 0) {
>  printk("minix_bmap: block<0\n");
>  } else if (block >= (minix_sb(inode->i_sb)->s_max_size/BLOCK_SIZE)) {
> -             printk("minix_bmap: block>big\n");
> +             if (printk_ratelimit())
> +                     printk("minix_bmap: block>big\n");

Warning: I'm only looking at the patch.

You are supposed to print an error message for a user, not to write in a
chat window to a 1337 script kiddie. OK, you just matched the current style,
and your patch is IMHO OK for a quick security fix, but:

- Security fixes should be CCed to the security mailing list, shouldn't they?
  (It might be security@ or stable@, I'll remember tomorrow, but then I'd
   forget to comment)
- Imagine you have three mounts containing a minix fs, how can you tell which
  one is the the defective one?
- The message says "minix_bmap", while the patch suggests it's in
  block_to_path. Therefore I asume "minix_bmap" to have only random
  informational value.
- Does block < 0 or block > $size make a difference?
- the printk lacks the loglevel.
- Asuming minix supports error handling, shouldn't it do something?

I'd suggest a message saying something like "minix: Bad block address on
device 08:15, needs fsck".
-- 
Oops. My brain just hit a bad sector. 

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