From: Jann Horn <jannh@google.com>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: kernel list <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
James Morris <jmorris@namei.org>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Matthew Garrett <mjg59@google.com>,
Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
mickael.salaun@ssi.gouv.fr, zohar@linux.ibm.com,
philippe.trebuchet@ssi.gouv.fr, shuah@kernel.org,
thibaut.sautereau@ssi.gouv.fr, vincent.strubel@ssi.gouv.fr,
yves-alexis.perez@ssi.gouv.fr,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Linux API <linux-api@vger.kernel.org>,
linux-security-module <linux-security-module@vger.kernel.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH v1 3/5] Yama: Enforces noexec mounts or file executability through O_MAYEXEC
Date: Wed, 12 Dec 2018 18:09:35 +0100 [thread overview]
Message-ID: <CAG48ez3SAW8EyaJ9T1U3qPoRhYwe4CCyL9bAxuc3GxjrXipi-A@mail.gmail.com> (raw)
In-Reply-To: <20181212081712.32347-4-mic@digikod.net>
On Wed, Dec 12, 2018 at 9:18 AM Mickaël Salaün <mic@digikod.net> wrote:
> Enable to either propagate the mount options from the underlying VFS
> mount to prevent execution, or to propagate the file execute permission.
> This may allow a script interpreter to check execution permissions
> before reading commands from a file.
>
> The main goal is to be able to protect the kernel by restricting
> arbitrary syscalls that an attacker could perform with a crafted binary
> or certain script languages. It also improves multilevel isolation
> by reducing the ability of an attacker to use side channels with
> specific code. These restrictions can natively be enforced for ELF
> binaries (with the noexec mount option) but require this kernel
> extension to properly handle scripts (e.g., Python, Perl).
>
> Add a new sysctl kernel.yama.open_mayexec_enforce to control this
> behavior. A following patch adds documentation.
>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Reviewed-by: Philippe Trébuchet <philippe.trebuchet@ssi.gouv.fr>
> Reviewed-by: Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Mickaël Salaün <mickael.salaun@ssi.gouv.fr>
> ---
[...]
> +/**
> + * yama_inode_permission - check O_MAYEXEC permission before accessing an inode
> + * @inode: inode structure to check
> + * @mask: permission mask
> + *
> + * Return 0 if access is permitted, -EACCES otherwise.
> + */
> +int yama_inode_permission(struct inode *inode, int mask)
This should be static, no?
> +{
> + if (!(mask & MAY_OPENEXEC))
> + return 0;
> + /*
> + * Match regular files and directories to make it easier to
> + * modify script interpreters.
> + */
> + if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
> + return 0;
So files are subject to checks, but loading code from things like
sockets is always fine?
> + if ((open_mayexec_enforce & YAMA_OMAYEXEC_ENFORCE_MOUNT) &&
> + !(mask & MAY_EXECMOUNT))
> + return -EACCES;
> +
> + /*
> + * May prefer acl_permission_check() instead of generic_permission(),
> + * to not be bypassable with CAP_DAC_READ_SEARCH.
> + */
> + if (open_mayexec_enforce & YAMA_OMAYEXEC_ENFORCE_FILE)
> + return generic_permission(inode, MAY_EXEC);
> +
> + return 0;
> +}
> +
> static struct security_hook_list yama_hooks[] __lsm_ro_after_init = {
> + LSM_HOOK_INIT(inode_permission, yama_inode_permission),
> LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
> LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
> LSM_HOOK_INIT(task_prctl, yama_task_prctl),
> @@ -447,6 +489,37 @@ static int yama_dointvec_minmax(struct ctl_table *table, int write,
> return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
> }
>
> +static int yama_dointvec_bitmask_macadmin(struct ctl_table *table, int write,
> + void __user *buffer, size_t *lenp,
> + loff_t *ppos)
> +{
> + int error;
> +
> + if (write) {
> + struct ctl_table table_copy;
> + int tmp_mayexec_enforce;
> +
> + if (!capable(CAP_MAC_ADMIN))
> + return -EPERM;
Don't put capable() checks in sysctls, it doesn't work.
next prev parent reply other threads:[~2018-12-12 17:09 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-12 8:17 [RFC PATCH v1 0/5] Add support for O_MAYEXEC Mickaël Salaün
2018-12-12 8:17 ` [RFC PATCH v1 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() Mickaël Salaün
2018-12-12 14:43 ` Jan Kara
2018-12-12 17:09 ` Mickaël Salaün
2018-12-12 20:42 ` Mimi Zohar
2018-12-13 9:47 ` Matthew Bobrowski
2018-12-13 14:23 ` Mickaël Salaün
2019-04-15 18:47 ` Steve Grubb
2019-04-16 11:49 ` Florian Weimer
2019-04-16 15:34 ` Steve Grubb
2019-04-17 10:01 ` Florian Weimer
2019-04-17 15:04 ` Mickaël Salaün
2019-04-17 14:55 ` Mickaël Salaün
2019-08-04 23:55 ` Andy Lutomirski
2019-08-06 16:40 ` Mickaël Salaün
2018-12-12 8:17 ` [RFC PATCH v1 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount propertie Mickaël Salaün
2018-12-12 8:17 ` [RFC PATCH v1 3/5] Yama: Enforces noexec mounts or file executability through O_MAYEXEC Mickaël Salaün
2018-12-12 14:28 ` Mickaël Salaün
2018-12-12 17:09 ` Jann Horn [this message]
2018-12-13 14:49 ` Mickaël Salaün
2019-01-03 11:17 ` Jann Horn
2019-01-08 13:29 ` Mickaël Salaün
2019-01-08 23:30 ` Kees Cook
2019-01-09 13:41 ` Mickaël Salaün
2018-12-12 8:17 ` [RFC PATCH v1 4/5] selftest/yama: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2018-12-12 8:17 ` [RFC PATCH v1 5/5] doc: Add documentation for Yama's open_mayexec_enforce Mickaël Salaün
2018-12-12 16:29 ` [RFC PATCH v1 0/5] Add support for O_MAYEXEC Jordan Glover
2018-12-12 17:01 ` Mickaël Salaün
2018-12-12 19:51 ` James Morris
2018-12-12 20:13 ` Florian Weimer
2018-12-12 23:40 ` James Morris
2018-12-13 5:13 ` Florian Weimer
2018-12-13 14:57 ` Mickaël Salaün
2018-12-13 3:02 ` Matthew Wilcox
2018-12-13 5:22 ` Florian Weimer
2018-12-13 11:04 ` Mimi Zohar
2018-12-13 11:26 ` Florian Weimer
2018-12-13 12:16 ` Mimi Zohar
2018-12-13 12:16 ` Matthew Wilcox
2018-12-13 15:17 ` Mickaël Salaün
2018-12-13 17:13 ` Matthew Wilcox
2018-12-13 17:36 ` Mickaël Salaün
2018-12-13 17:44 ` Matthew Wilcox
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