Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 27 Nov 2017 21:29:25 -0800
From:   Andrei Vagin <avagin@virtuozzo.com>
To:     Alexey Dobriyan <adobriyan@gmail.com>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        xemul@virtuozzo.com
Subject: Re: proc: fix /proc/*/map_files lookup
Message-ID: <20171128052924.GA7047@outlook.office365.com>
References: <20171120212706.GA14325@avx2>
MIME-Version: 1.0
Content-Type: text/plain; charset=koi8-r
Content-Disposition: inline
In-Reply-To: <20171120212706.GA14325@avx2>
User-Agent: Mutt/1.9.1 (2017-09-22)
Received-SPF: None (protection.outlook.com: virtuozzo.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Nov 2017 05:29:34.3407 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 78507ee7-352d-4c6a-b311-08d53621032d
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f
X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR08MB0746
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Nov 21, 2017 at 12:27:06AM +0300, Alexey Dobriyan wrote:
> Current code does:
> 
> 	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)
> 
> However sscanf() is broken garbage.
> 
> It silently accepts whitespace between format specifiers
> (did you know that?).
> 
> It silently accepts valid strings which result in integer overflow.
> 
> Do not use sscanf() for any even remotely reliable parsing code.

This patch breaks criu, criu has one places where a file name is generated
as map_files/%p-%p

openat(1048572, "map_files/0x7f9912dd5000-0x7f9912de4000", O_RDWR) = -1 ENOENT (No such file or directory) <0.000015>

And this code worked before this patch and it doesn't work with this
patch. And you have to know that we never break user-space programs ;)

But seriously, the patch looks good to me, but I would prefer to not queue
it into stable kernels.

Thanks,
Andrei


> 
> 	OK
> 	# readlink '/proc/1/map_files/55a23af39000-55a23b05b000'
> 	/lib/systemd/systemd
> 
> 	broken
> 	# readlink '/proc/1/map_files/               55a23af39000-55a23b05b000'
> 	/lib/systemd/systemd
> 
> 	broken
> 	# readlink '/proc/1/map_files/55a23af39000-55a23b05b000    '
> 	/lib/systemd/systemd
> 
> 	very broken
> 	# readlink '/proc/1/map_files/1000000000000000055a23af39000-55a23b05b000'
> 	/lib/systemd/systemd
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: stable@kernel.org
> ---
> 
>  fs/proc/base.c |   29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -100,6 +100,8 @@
>  #include "internal.h"
>  #include "fd.h"
>  
> +#include "../../lib/kstrtox.h"
> +
>  /* NOTE:
>   *	Implementing inode permission operations in /proc is almost
>   *	certainly an error.  Permission checks need to happen during
> @@ -1907,8 +1909,33 @@ bool proc_fill_cache(struct file *file, struct dir_context *ctx,
>  static int dname_to_vma_addr(struct dentry *dentry,
>  			     unsigned long *start, unsigned long *end)
>  {
> -	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)
> +	const char *str = dentry->d_name.name;
> +	unsigned long long sval, eval;
> +	unsigned int len;
> +
> +	len = _parse_integer(str, 16, &sval);
> +	if (len & KSTRTOX_OVERFLOW)
> +		return -EINVAL;
> +	if (sval != (unsigned long)sval)
> +		return -EINVAL;
> +	str += len;
> +
> +	if (*str != '-')
>  		return -EINVAL;
> +	str++;
> +
> +	len = _parse_integer(str, 16, &eval);
> +	if (len & KSTRTOX_OVERFLOW)
> +		return -EINVAL;
> +	if (eval != (unsigned long)eval)
> +		return -EINVAL;
> +	str += len;
> +
> +	if (*str != '\0')
> +		return -EINVAL;
> +
> +	*start = sval;
> +	*end = eval;
>  
>  	return 0;
>  }

From 1584653559919789070@xxx Tue Nov 21 05:50:00 +0000 2017
X-GM-THRID: 1584621974020232218
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread