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From: "Mickaël Salaün" <mic@digikod.net>
To: Jann Horn <jannh@google.com>
Cc: "kernel list" <linux-kernel@vger.kernel.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"James Morris" <jmorris@namei.org>, "Jann Horn" <jann@thejh.net>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Kees Cook" <keescook@chromium.org>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vincent Dagonneau" <vincent.dagonneau@ssi.gouv.fr>,
	"Kernel Hardening" <kernel-hardening@lists.openwall.com>,
	"Linux API" <linux-api@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-doc@vger.kernel.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK"
	<linux-kselftest@vger.kernel.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [RFC PATCH v14 05/10] fs,landlock: Support filesystem access-control
Date: Thu, 27 Feb 2020 17:50:31 +0100	[thread overview]
Message-ID: <34319b76-44bd-8915-fd7c-5147f901615e@digikod.net> (raw)
In-Reply-To: <CAG48ez36SMrPPgsj0omcVukRLwOzBzqWOQjuGCmmmrmsGiNukw@mail.gmail.com>



On 26/02/2020 21:29, Jann Horn wrote:
> On Mon, Feb 24, 2020 at 5:03 PM Mickaël Salaün <mic@digikod.net> wrote:
>> +static inline u32 get_mem_access(unsigned long prot, bool private)
>> +{
>> +       u32 access = LANDLOCK_ACCESS_FS_MAP;
>> +
>> +       /* Private mapping do not write to files. */
>> +       if (!private && (prot & PROT_WRITE))
>> +               access |= LANDLOCK_ACCESS_FS_WRITE;
>> +       if (prot & PROT_READ)
>> +               access |= LANDLOCK_ACCESS_FS_READ;
>> +       if (prot & PROT_EXEC)
>> +               access |= LANDLOCK_ACCESS_FS_EXECUTE;
>> +       return access;
>> +}
> 
> When I do the following, is landlock going to detect that the mmap()
> is a read access, or is it incorrectly going to think that it's
> neither read nor write?
> 
> $ cat write-only.c
> #include <fcntl.h>
> #include <sys/mman.h>
> #include <stdio.h>
> int main(void) {
>   int fd = open("/etc/passwd", O_RDONLY);
>   char *ptr = mmap(NULL, 0x1000, PROT_WRITE, MAP_PRIVATE, fd, 0);
>   printf("'%.*s'\n", 4, ptr);
> }
> $ gcc -o write-only write-only.c -Wall
> $ ./write-only
> 'root'
> $
> 

Thanks to the "if (!private && (prot & PROT_WRITE))", Landlock allows
this private mmap (as intended) even if there is no write access to this
file, but not with a shared mmap (and a file opened with O_RDWR). I just
added a test for this to be sure.

However, I'm not sure this hook is useful for now. Indeed, the process
still need to have a file descriptor open with the right accesses.

  reply	other threads:[~2020-02-27 16:51 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-24 16:02 [RFC PATCH v14 00/10] Landlock LSM Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 01/10] landlock: Add object and rule management Mickaël Salaün
2020-02-25 20:49   ` Jann Horn
2020-02-26 15:31     ` Mickaël Salaün
2020-02-26 20:24       ` Jann Horn
2020-02-27 16:46         ` Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 02/10] landlock: Add ruleset and domain management Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 03/10] landlock: Set up the security framework and manage credentials Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 04/10] landlock: Add ptrace restrictions Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 05/10] fs,landlock: Support filesystem access-control Mickaël Salaün
2020-02-26 20:29   ` Jann Horn
2020-02-27 16:50     ` Mickaël Salaün [this message]
2020-02-27 16:51       ` Jann Horn
2020-02-24 16:02 ` [RFC PATCH v14 06/10] landlock: Add syscall implementation Mickaël Salaün
2020-03-17 16:47   ` Al Viro
2020-03-17 17:51     ` Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 07/10] arch: Wire up landlock() syscall Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 08/10] selftests/landlock: Add initial tests Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 09/10] samples/landlock: Add a sandbox manager example Mickaël Salaün
2020-02-24 16:02 ` [RFC PATCH v14 10/10] landlock: Add user and kernel documentation Mickaël Salaün
2020-02-29 17:23   ` Randy Dunlap
2020-03-02 10:03     ` Mickaël Salaün
2020-02-25 18:49 ` [RFC PATCH v14 00/10] Landlock LSM J Freyensee
2020-02-26 15:34   ` Mickaël Salaün
     [not found] ` <20200227042002.3032-1-hdanton@sina.com>
2020-02-27 17:01   ` [RFC PATCH v14 01/10] landlock: Add object and rule management Mickaël Salaün
2020-03-09 23:44 ` [RFC PATCH v14 00/10] Landlock LSM Jann Horn
2020-03-11 23:38   ` Mickaël Salaün
2020-03-17 16:19     ` Jann Horn
2020-03-17 17:50       ` Mickaël Salaün
2020-03-17 19:45         ` Jann Horn
2020-03-18 12:06           ` Mickaël Salaün
2020-03-18 23:33             ` Jann Horn
2020-03-19 16:58               ` Mickaël Salaün
2020-03-19 21:17                 ` Jann Horn
2020-03-30 18:26                   ` Mickaël Salaün

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