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Message-ID: <e75185e6-9b16-82a8-5d9b-cdfdc60962bf@schaufler-ca.com>
Date: Fri, 25 Nov 2022 10:27:02 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: Mickaël Salaün <mic@...ikod.net>,
casey.schaufler@...el.com, paul@...l-moore.com,
linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org, keescook@...omium.org,
john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org, casey@...aufler-ca.com
Subject: Re: [PATCH v3 2/9] LSM: Identify the process attributes for each
module
On 11/25/2022 8:41 AM, Mickaël Salaün wrote:
>
> On 23/11/2022 21:15, Casey Schaufler wrote:
>> Add an integer member "attrs_used" to the struct lsm_id which
>> identifies the API related data associated with each security
>> module. The initial set of features maps to information that
>> has traditionaly been available in /proc/self/attr. They are
>> documented in a new userspace-api file.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> ---
>> Documentation/userspace-api/index.rst | 1 +
>> Documentation/userspace-api/lsm.rst | 55 +++++++++++++++++++++++++++
>> include/linux/lsm_hooks.h | 2 +
>> include/uapi/linux/lsm.h | 12 ++++++
>> security/apparmor/lsm.c | 1 +
>> security/selinux/hooks.c | 2 +
>> security/smack/smack_lsm.c | 1 +
>> 7 files changed, 74 insertions(+)
>> create mode 100644 Documentation/userspace-api/lsm.rst
>>
>> diff --git a/Documentation/userspace-api/index.rst
>> b/Documentation/userspace-api/index.rst
>> index c78da9ce0ec4..6feff0fcd88f 100644
>> --- a/Documentation/userspace-api/index.rst
>> +++ b/Documentation/userspace-api/index.rst
>> @@ -30,6 +30,7 @@ place where this information is gathered.
>> sysfs-platform_profile
>> vduse
>> futex2
>> + lsm
>> .. only:: subproject and html
>> diff --git a/Documentation/userspace-api/lsm.rst
>> b/Documentation/userspace-api/lsm.rst
>> new file mode 100644
>> index 000000000000..6ddf5506110b
>> --- /dev/null
>> +++ b/Documentation/userspace-api/lsm.rst
>> @@ -0,0 +1,55 @@
>> +.. SPDX-License-Identifier: GPL-2.0
>> +.. Copyright (C) 2022 Casey Schaufler <casey@...aufler-ca.com>
>> +.. Copyright (C) 2022 Intel Corporation
>> +
>> +=====================================
>> +Linux Security Modules
>> +=====================================
>> +
>> +:Author: Casey Schaufler
>> +:Date: November 2022
>> +
>> +Linux security modules (LSM) provide a mechanism to implement
>> +additional access controls to the Linux security policies.
>> +
>> +The various security modules may support any of these attributes:
>> +
>> +``LSM_ATTR_CURRENT`` is the current, active security context of the
>> +process.
>> +The proc filesystem provides this value in ``/proc/self/attr/current``.
>> +This is supported by the SELinux, Smack and AppArmor security modules.
>> +Smack also provides this value in ``/proc/self/attr/smack/current``.
>> +AppArmor also provides this value in
>> ``/proc/self/attr/apparmor/current``.
>> +
>> +``LSM_ATTR_EXEC`` is the security context of the process at the time
>> the
>> +current image was executed.
>> +The proc filesystem provides this value in ``/proc/self/attr/exec``.
>> +This is supported by the SELinux and AppArmor security modules.
>> +AppArmor also provides this value in ``/proc/self/attr/apparmor/exec``.
>> +
>> +``LSM_ATTR_FSCREATE`` is the security context of the process used when
>> +creating file system objects.
>> +The proc filesystem provides this value in
>> ``/proc/self/attr/fscreate``.
>> +This is supported by the SELinux security module.
>> +
>> +``LSM_ATTR_KEYCREATE`` is the security context of the process used when
>> +creating key objects.
>> +The proc filesystem provides this value in
>> ``/proc/self/attr/keycreate``.
>> +This is supported by the SELinux security module.
>> +
>> +``LSM_ATTR_PREV`` is the security context of the process at the time
>> the
>> +current security context was set.
>> +The proc filesystem provides this value in ``/proc/self/attr/prev``.
>> +This is supported by the SELinux and AppArmor security modules.
>> +AppArmor also provides this value in ``/proc/self/attr/apparmor/prev``.
>> +
>> +``LSM_ATTR_SOCKCREATE`` is the security context of the process used
>> when
>> +creating socket objects.
>> +The proc filesystem provides this value in
>> ``/proc/self/attr/sockcreate``.
>> +This is supported by the SELinux security module.
>> +
>> +Additional documentation
>> +========================
>> +
>> +* Documentation/security/lsm.rst
>> +* Documentation/security/lsm-development.rst
>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
>> index d306db1044d1..7e88acc37a29 100644
>> --- a/include/linux/lsm_hooks.h
>> +++ b/include/linux/lsm_hooks.h
>> @@ -1606,12 +1606,14 @@ struct security_hook_heads {
>> * struct lsm_id - identify a Linux Security Module.
>> * @lsm: Name of the LSM. Must be approved by the LSM maintainers.
>> * @id: LSM ID number from uapi/linux/lsm.h
>> + * @attrs_used: Which attributes this LSM supports.
>> *
>> * Contains the information that identifies the LSM.
>> */
>> struct lsm_id {
>> const u8 *lsm;
>> u32 id;
>> + u64 attrs_used;
>
> I'd prefer this field to be part of the previous patch. This doesn't
> change much but it is to highlight that the struct lsm_id size should
> not change unless properly handled by userspace.
Sigh. Given my druthers there would be a lot fewer, but somewhat larger, patches
in this set. I will happily make this change, but fear reprisal from those who
want a bizzilion tiny patches. (You know who you are) Also note that this is not
an externally visible structure, and that the lsm_ctx structure that is user
visible hasn't been introduced yet.
>
>
>> };
>> /*
>> diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h
>> index 47791c330cbf..8e9124bf622c 100644
>> --- a/include/uapi/linux/lsm.h
>> +++ b/include/uapi/linux/lsm.h
>> @@ -29,4 +29,16 @@
>> #define LSM_ID_BPF 110
>> #define LSM_ID_LANDLOCK 111
>> +/*
>> + * LSM_ATTR_XXX values identify the /proc/.../attr entry that the
>> + * context represents. Not all security modules provide all of these
>> + * values. Some security modules provide none of them.
>> + */
>> +#define LSM_ATTR_CURRENT 0x0001
>> +#define LSM_ATTR_EXEC 0x0002
>> +#define LSM_ATTR_FSCREATE 0x0004
>> +#define LSM_ATTR_KEYCREATE 0x0008
>> +#define LSM_ATTR_PREV 0x0010
>> +#define LSM_ATTR_SOCKCREATE 0x0020
>> +
>> #endif /* _UAPI_LINUX_LSM_H */
>> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
>> index b859b1af6c75..3a6bf4f95d84 100644
>> --- a/security/apparmor/lsm.c
>> +++ b/security/apparmor/lsm.c
>> @@ -1206,6 +1206,7 @@ struct lsm_blob_sizes apparmor_blob_sizes
>> __lsm_ro_after_init = {
>> static struct lsm_id apparmor_lsmid __lsm_ro_after_init = {
>> .lsm = "apparmor",
>> .id = LSM_ID_APPARMOR,
>> + .attrs_used = LSM_ATTR_CURRENT | LSM_ATTR_PREV | LSM_ATTR_EXEC,
>> };
>> static struct security_hook_list apparmor_hooks[]
>> __lsm_ro_after_init = {
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 5fcce36267bd..e831d9c38c54 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -7018,6 +7018,8 @@ static int selinux_uring_cmd(struct
>> io_uring_cmd *ioucmd)
>> static struct lsm_id selinux_lsmid __lsm_ro_after_init = {
>> .lsm = "selinux",
>> .id = LSM_ID_SELINUX,
>> + .attrs_used = LSM_ATTR_CURRENT | LSM_ATTR_EXEC |
>> LSM_ATTR_FSCREATE |
>> + LSM_ATTR_KEYCREATE | LSM_ATTR_PREV | LSM_ATTR_SOCKCREATE,
>> };
>> /*
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index c7ba80e20b8d..c2a05217bde4 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -4791,6 +4791,7 @@ struct lsm_blob_sizes smack_blob_sizes
>> __lsm_ro_after_init = {
>> static struct lsm_id smack_lsmid __lsm_ro_after_init = {
>> .lsm = "smack",
>> .id = LSM_ID_SMACK,
>> + .attrs_used = LSM_ATTR_CURRENT,
>> };
>> static struct security_hook_list smack_hooks[]
>> __lsm_ro_after_init = {
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