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Message-ID: <CAG48ez36SMrPPgsj0omcVukRLwOzBzqWOQjuGCmmmrmsGiNukw@mail.gmail.com>
Date: Wed, 26 Feb 2020 21:29:18 +0100
From: Jann Horn <jannh@...gle.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: kernel list <linux-kernel@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...capital.net>, Arnd Bergmann <arnd@...db.de>,
Casey Schaufler <casey@...aufler-ca.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
James Morris <jmorris@...ei.org>, Jann Horn <jann@...jh.net>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>, Michael Kerrisk <mtk.manpages@...il.com>,
Mickaël Salaün <mickael.salaun@....gouv.fr>,
"Serge E . Hallyn" <serge@...lyn.com>, Shuah Khan <shuah@...nel.org>,
Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>, linux-doc@...r.kernel.org,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>,
linux-security-module <linux-security-module@...r.kernel.org>,
"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [RFC PATCH v14 05/10] fs,landlock: Support filesystem access-control
On Mon, Feb 24, 2020 at 5:03 PM Mickaël Salaün <mic@...ikod.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'
$
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