Re: [PATCH v3 2/9] LSM: Identify the process attributes for each module

[Casey Schaufler]

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@xxxxxxxxxxxxxxxx>
>> ---
>>   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@xxxxxxxxxxxxxxxx>
>> +.. 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 = {