Re: [PATCH v24 00/25] LSM: Module stacking for AppArmor
From: Topi Miettinen
Date: Tue Feb 02 2021 - 12:15:54 EST
On 2.2.2021 17.30, Casey Schaufler wrote:
On 2/2/2021 4:05 AM, Topi Miettinen wrote:
On 26.1.2021 18.40, Casey Schaufler wrote:
This patchset provides the changes required for
the AppArmor security module to stack safely with any other.
In my test, when kernel command line has apparmor before selinux in lsm= entry, the boot is not successful with enforcing=1:
systemd[1]: Failed to compute init label, ignoring.
systemd[1]: Failed to set SELinux security context system_u:object_r:cgroup_t:s0 for /sys/fs/cgroup: Invalid argument
systemd[1]: Failed to set SELinux security context system_u:object_r:pstore_t:s0 for /sys/fs/pstore: Invalid argument
systemd[1]: Failed to set SELinux security context system_u:object_r:sysfs_t:s0 for /sys/firmware/efi/efivars: Invalid argument
...
Failed to drop capability bounding set of usermode helpers: Operation not permitted
Failed to drop capability bounding set of usermode helpers.
systemd[1]: Freezing execution.
Systemd has extensive support for SELinux. That's good.
It doesn't have an understanding of what needs to be done
if SELinux is active but not the default security module
for interfaces including SO_PEERSEC and /proc/*/attr/*.
That's going to take some work.
Ok. What will be the replacement for SO_PEERSEC? Systemd calls
getsockopt(fd, SOL_SOCKET, SO_PEERSEC, s, &n).
Is the /proc part something that should be fixed on systemd side, or can
perhaps the SELinux libraries hide this from applications?
Probably SELinux libraries can't find or set the labels for the PID1 or any file systems. Before the init label message, systemd calls getcon_raw(), getfilecon_raw(), string_to_security_class() and security_compute_create_raw(), so one of these don't understand the LSM stacking.
That is correct.
Also the policy needs updating to handle process2:setdisplay:
SELinux: Permission setdisplay in class process2 not defined in policy.
SELinux: the above unknown classes and permissions will be denied
With enforcing=0, many services start, but for example systemd-journald doesn't. This is probably related to the earlier problem with labels (maybe libraries try to use SELinux labels where kernel wants AppArmor profiles):
systemd[1]: Failed to set SELinux security context system_u:object_r:init_runtime_t:s0 for /run/systemd/units/invocation:systemd-user-sessions.service: Invalid argument
This is also an artifact of systemd seeing AppArmor information
instead of SELinux contexts.
Will SELinux libraries choose automatically the correct way to set
labels in the future?
Switching the order so that apparmor is after selinux, boot is successful. Loading AppArmor profiles needs a permission from SELinux:
Feb 02 08:53:15 audit[963]: AVC avc: denied { mac_admin } for pid=963 comm="apparmor_parser" capability=33 scontext=system_u:system_r:initrc_t:s0 tcontext=system_u:system_r:initrc_t:s0 tclass=capability2 permissive=0
Feb 02 08:53:15 audit[963]: AVC apparmor="STATUS" operation="profile_replace" info="not policy admin" error=-13 profile="unconfined" pid=963 comm="apparmor_parser"
Feb 02 08:53:15 audit: AUDIT1420 subj_selinux=system_u:system_r:initrc_t:s0 subj_apparmor==unconfined
Feb 02 08:53:15 audit[963]: SYSCALL arch=c000003e syscall=1 success=no exit=-13 a0=7 a1=7a8f2ff04f80 a2=1e09 a3=0 items=0 ppid=961 pid=963 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="apparmor_parser" exe="/usr/sbin/apparmor_parser" subj=? key=(null)
Feb 02 08:53:15 audit: PROCTITLE proctitle=2F7362696E2F61707061726D6F725F706172736572002D2D77726974652D6361636865002D2D7265706C616365002D2D002F6574632F61707061726D6F722E64
Feb 02 08:53:15 apparmor.systemd[963]: /sbin/apparmor_parser: Unable to replace "/lib/systemd/systemd-resolved". Permission denied; attempted to load a profile while confined?
This just seems to need TE rules for the apparmor_parser.
Double equal sign in subj_apparmor==unconfined looks odd, should that be just one like subj_selinux?
The audit code is reporting what AppArmor provides.
I agree that this looks odd.
Tools like ps, and KDE and Gnome System Monitors only show SELinux context, but it would be nice if MAC contexts for all enabled LSMs were shown.
I agree. How this should be done has been a topic of
lively debate for some time.
-Topi
Thank you for this report. Which distribution are you using?
I have been testing with Fedora (SELinux + AppArmor) and Ubuntu
(AppArmor + Smack). I would be very interested to see how a
distribution that doesn't use systemd behaves.
This is Debian with systemd, I'm using SELinux + TOMOYO + AppArmor.
-Topi
v24: Rebase to 5.11-rc1
Incorporate feedback from v23
- Address the IMA team's concerns about "label collisions".
A label collision occurs when there is ambiguity about
which of multiple LSMs is being targeted in the definition
of an integrity check rule. A system with Smack and
AppArmor would be unable to distinguish which LSM is
important to an integrity rule referrencing the label
"unconfined" as that label is meaningful to both.
Provide a boot option to specify which LSM will be used in
IMA rules when multiple LSMs are present. (patch 04)
Pull LSM "slot" identification from later audit patches in
in support of this (patch 03).
- Pick up a few audit events that need to include supplimental
subject context records that had been missed in the
previous version.
v23: Rebase to 5.10-rc4
Incorporate feedback from v22
- Change /proc/*/attr/display to /proc/*/attr/interface_lsm to
make the purpose clearer. (patch 0012)
- Include ABI documentation. (patch 0012, 0022)
- Introduce LSM documentation updates with the patches where
the interfaces are added rather than at the end. (patch 0012, 0022)
Include more maintainers and mail lists in To: and Cc: directives.
v22: Rebase to 5.10-rc1
v21: Rebase to 5.9-rc4
Incorporate feedback from v20
- Further revert UDS SO_PEERSEC to use scaffolding around
the interfaces that use lsmblobs and store only a single
secid. The possibility of multiple security modules
requiring data here is still a future problem.
- Incorporate Richard Guy Briggs' non-syscall auxiliary
records patch (patch 0019-0021) in place of my "supplimental"
records implementation. [I'm not sure I've given proper
attestation. I will correct as appropriate]
v20: Rebase to 5.9-rc1
Change the BPF security module to use the lsmblob data. (patch 0002)
Repair length logic in subject label processing (patch 0015)
Handle -EINVAL from the empty BPF setprocattr hook (patch 0020)
Correct length processing in append_ctx() (patch 0022)
v19: Rebase to 5.8-rc6
Incorporate feedback from v18
- Revert UDS SO_PEERSEC implementation to use lsmblobs
directly, rather than allocating as needed. The correct
treatment of out-of-memory conditions in the later case
is difficult to define. (patch 0005)
- Use a size_t in append_ctx() (patch 0021)
- Fix a memory leak when creating compound contexts. (patch 0021)
Fix build error when CONFIG_SECURITY isn't set (patch 0013)
Fix build error when CONFIG_SECURITY isn't set (patch 0020)
Fix build error when CONFIG_SECURITY isn't set (patch 0021)
v18: Rebase to 5.8-rc3
Incorporate feedback from v17
- Null pointer checking in UDS (patch 0005)
Match changes in IMA code (patch 0012)
Fix the behavior of LSM context supplimental audit
records so that there's always exactly one when it's
appropriate for there to be one. This is a substantial
change that requires extention of the audit_context beyond
syscall events. (patch 0020)
v17: Rebase to 5.7-rc4
v16: Rebase to 5.6
Incorporate feedback from v15 - Thanks Stephen, Mimi and Paul
- Generally improve commit messages WRT scaffolding
- Comment ima_lsm_isset() (patch 0002)
- Some question may remain on IMA warning (patch 0002)
- Mark lsm_slot as __lsm_ro_after_init not __init_data (patch 0002)
- Change name of lsmblob variable in ima_match_rules() (patch 0003)
- Instead of putting a struct lsmblob into the unix_skb_parms
structure put a pointer to an allocated instance. There is
currently only space for 5 u32's in unix_skb_parms and it is
likely to get even tighter. Fortunately, the lifecycle
management of the allocated lsmblob is simple. (patch 0005)
- Dropped Acks due to the above change (patch 0005)
- Improved commentary on secmark labeling scaffolding. (patch 0006)
- Reduced secmark related labeling scaffolding. (patch 0006)
- Replace use of the zeroth entry of an lsmblob in scaffolding
with a function lsmblob_value() to hopefully make it less
obscure. (patch 0006)
- Convert security_secmark_relabel_packet to use lsmblob as
this reduces much of the most contentious scaffolding. (patch 0006)
- Dropped Acks due to the above change (patch 0006)
- Added BUILD_BUG_ON() for CIPSO tag 6. (patch 0018)
- Reworked audit subject information. Instead of adding fields in
the middle of existing records add a new record to the event. When
a separate record is required use subj="?". (patch 0020)
- Dropped Acks due to the above change (patch 0020)
- Reworked audit object information. Instead of adding fields in
the middle of existing records add a new record to the event. When
a separate record is required use obj="?". (patch 0021)
- Dropped Acks due to the above change (patch 0021)
- Enhanced documentation (patch 0022)
- Removed unnecessary error code check in security_getprocattr()
(patch 0021)
v15: Rebase to 5.6-rc1
- Revise IMA data use (patch 0002)
Incorporate feedback from v14
- Fix lockdown module registration naming (patch 0002)
- Revise how /proc/self/attr/context is gathered. (patch 0022)
- Revise access modes on /proc/self/attr/context. (patch 0022)
- Revise documentation on LSM external interfaces. (patch 0022)
v14: Rebase to 5.5-rc5
Incorporate feedback from v13
- Use an array of audit rules (patch 0002)
- Significant change, removed Acks (patch 0002)
- Remove unneeded include (patch 0013)
- Use context.len correctly (patch 0015)
- Reorder code to be more sensible (patch 0016)
- Drop SO_PEERCONTEXT as it's not needed yet (patch 0023)
v13: Rebase to 5.5-rc2
Incorporate feedback from v12
- Print lsmblob size with %z (Patch 0002)
- Convert lockdown LSM initialization. (Patch 0002)
- Restore error check in nft_secmark_compute_secid (Patch 0006)
- Correct blob scaffolding in ima_must_appraise() (Patch 0009)
- Make security_setprocattr() clearer (Patch 0013)
- Use lsm_task_display more widely (Patch 0013)
- Use passed size in lsmcontext_init() (Patch 0014)
- Don't add a smack_release_secctx() hook (Patch 0014)
- Don't print warning in security_release_secctx() (Patch 0014)
- Don't duplicate the label in nfs4_label_init_security() (Patch 0016)
- Remove reviewed-by as code has significant change (Patch 0016)
- Send the entire lsmblob for Tag 6 (Patch 0019)
- Fix description of socket_getpeersec_stream parameters (Patch 0023)
- Retain LSMBLOB_FIRST. What was I thinking? (Patch 0023)
- Add compound context to LSM documentation (Patch 0023)
v12: Rebase to 5.5-rc1
Fixed a couple of incorrect contractions in the text.
v11: Rebase to 5.4-rc6
Incorporate feedback from v10
- Disambiguate reading /proc/.../attr/display by restricting
all use of the interface to the current process.
- Fix a merge error in AppArmor's display attribute check
v10: Ask the security modules if the display can be changed.
v9: There is no version 9
v8: Incorporate feedback from v7
- Minor clean-up in display value management
- refactor "compound" context creation to use a common
append_ctx() function.
v7: Incorporate feedback from v6
- Make setting the display a privileged operation. The
availability of compound contexts reduces the need for
setting the display.
v6: Incorporate feedback from v5
- Add subj_<lsm>= and obj_<lsm>= fields to audit records
- Add /proc/.../attr/context to get the full context in
lsmname\0value\0... format as suggested by Simon McVittie
- Add SO_PEERCONTEXT for getsockopt() to get the full context
in the same format, also suggested by Simon McVittie.
- Add /sys/kernel/security/lsm_display_default to provide
the display default value.
v5: Incorporate feedback from v4
- Initialize the lsmcontext in security_secid_to_secctx()
- Clear the lsmcontext in all security_release_secctx() cases
- Don't use the "display" on strictly internal context
interfaces.
- The SELinux binder hooks check for cases where the context
"display" isn't compatible with SELinux.
v4: Incorporate feedback from v3
- Mark new lsm_<blob>_alloc functions static
- Replace the lsm and slot fields of the security_hook_list
with a pointer to a LSM allocated lsm_id structure. The
LSM identifies if it needs a slot explicitly. Use the
lsm_id rather than make security_add_hooks return the
slot value.
- Validate slot values used in security.c
- Reworked the "display" process attribute handling so that
it works right and doesn't use goofy list processing.
- fix display value check in dentry_init_security
- Replace audit_log of secids with '?' instead of deleting
the audit log
v3: Incorporate feedback from v2
- Make lsmblob parameter and variable names more
meaningful, changing "le" and "l" to "blob".
- Improve consistency of constant naming.
- Do more sanity checking during LSM initialization.
- Be a bit clearer about what is temporary scaffolding.
- Rather than clutter security_getpeersec_dgram with
otherwise unnecessary checks remove the apparmor
stub, which does nothing useful.
Patch 01 moves management of the sock security blob
from the individual modules to the infrastructure.
Patches 02-03 introduce a structure "lsmblob" that will gradually
replace the "secid" as a shorthand for security module information.
At this point lsmblob contains an array of u32 secids, one "slot"
for each of the security modules compiled into the kernel that
used secids. A "slot" is allocated when a security module requests
one.
Patch 04 provides mechanism for the IMA subsystem to identify
explicitly which LSM is subject to IMA policy. This includes
a boot option for specifying the default and an additional option
in IMA rules "lsm=".
Patches 05-13 change LSM interfaces to use the lsmblob instead
of secids. It is important that the lsmblob be a fixed size entity
that does not have to be allocated. Several of the places
where it is used would have performance and/or locking
issues with dynamic allocation.
Patch 14 provides a mechanism for a process to identify which
security module's hooks should be used when displaying or
converting a security context string. A new interface
/proc/self/attr/interface_lsm contains the name of the security
module to show. Reading from this file will present the name of
the module, while writing to it will set the value. Only names
of active security modules are accepted. Internally, the name
is translated to the appropriate "slot" number for the module
which is then stored in the task security blob. Setting the
display requires that all modules using the /proc interfaces
allow the transition. The interface LSM of other processess
can be neither read nor written. All suggested cases for
reading the interface LSM of a different process have race
conditions.
Patch 15 Starts the process of changing how a security
context is represented. Since it is possible for a
security context to have been generated by more than one
security module it is now necessary to note which module
created a security context so that the correct "release"
hook can be called. There are several places where the
module that created a security context cannot be inferred.
This is achieved by introducing a "lsmcontext" structure
which contains the context string, its length and the
"slot" number of the security module that created it.
The security_release_secctx() interface is changed,
replacing the (string,len) pointer pair with a lsmcontext
pointer.
Patches 16-18 convert the security interfaces from
(string,len) pointer pairs to a lsmcontext pointer.
The slot number identifying the creating module is
added by the infrastructure. Where the security context
is stored for extended periods the data type is changed.
The Netlabel code is converted to save lsmblob structures
instead of secids in Patch 19. This is not strictly
necessary as there can only be one security module that
uses Netlabel at this point. Using a lsmblob is much
cleaner, as the interfaces that use the data have all
been converted.
Patch 20 adds checks to the binder hooks which verify
that both ends of a transaction use the same interface LSM.
Patches 21-23 add addition audit records for subject and
object LSM data when there are multiple security modules
with such data. The AUDIT_MAC_TASK_CONTEXTS record is used
in conjuction with a "subj=?" field to identify the subject
data. The AUDIT_MAC_OBJ_CONTEXTS record is used in conjuction
with a "obj=?" field to identify the object data. The
AUDIT_MAC_TASK_CONTEXTS record identifies the security module
with the data: "subj_selinux=xyz_t subj_apparmor=abc". The
AUDIT_MAC_OBJ_CONTEXTS record identifies the security module
with the data: "obj_selinux=xyz_t obj_apparmor=abc". While
AUDIT_MAC_TASK_CONTEXTS records will always contain an entry
for each possible security modules, AUDIT_MAC_OBJ_CONTEXTS
records will only contain entries for security modules for
which the object in question has data.
An example of the MAC_TASK_CONTEXTS (1420) record is:
type=UNKNOWN[1420]
msg=audit(1600880931.832:113)
subj_apparmor==unconfined
subj_smack=_
An example of the MAC_OBJ_CONTEXTS (1421) record is:
type=UNKNOWN[1421]
msg=audit(1601152467.009:1050):
obj_selinux=unconfined_u:object_r:user_home_t:s0
Patch 24 adds a new interface for getting the compound security
contexts, /proc/self/attr/context. An example of the content
of this file is:
selinux\0one_u:one_r:one_t:s0-s0:c0.c1023\0apparmor\0unconfined\0
Finally, with all interference on the AppArmor hooks removed,
Patch 25 removes the exclusive bit from AppArmor. An unnecessary
stub hook was also removed.
The Ubuntu project is using an earlier version of this patchset in
their distribution to enable stacking for containers.
Performance measurements to date have the change within the "noise".
The sockperf and dbench results are on the order of 0.2% to 0.8%
difference, with better performance being as common as worse. The
benchmarks were run with AppArmor and Smack on Ubuntu.
https://github.com/cschaufler/lsm-stacking.git#stack-5.11-rc1-v24
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Casey Schaufler (25):
LSM: Infrastructure management of the sock security
LSM: Add the lsmblob data structure.
LSM: provide lsm name and id slot mappings
IMA: avoid label collisions with stacked LSMs
LSM: Use lsmblob in security_audit_rule_match
LSM: Use lsmblob in security_kernel_act_as
LSM: Use lsmblob in security_secctx_to_secid
LSM: Use lsmblob in security_secid_to_secctx
LSM: Use lsmblob in security_ipc_getsecid
LSM: Use lsmblob in security_task_getsecid
LSM: Use lsmblob in security_inode_getsecid
LSM: Use lsmblob in security_cred_getsecid
IMA: Change internal interfaces to use lsmblobs
LSM: Specify which LSM to display
LSM: Ensure the correct LSM context releaser
LSM: Use lsmcontext in security_secid_to_secctx
LSM: Use lsmcontext in security_inode_getsecctx
LSM: security_secid_to_secctx in netlink netfilter
NET: Store LSM netlabel data in a lsmblob
LSM: Verify LSM display sanity in binder
audit: add support for non-syscall auxiliary records
Audit: Add new record for multiple process LSM attributes
Audit: Add a new record for multiple object LSM attributes
LSM: Add /proc attr entry for full LSM context
AppArmor: Remove the exclusive flag
Documentation/ABI/testing/ima_policy | 8 +-
Documentation/ABI/testing/procfs-attr-context | 14 +
.../ABI/testing/procfs-attr-lsm_display | 22 +
Documentation/security/lsm.rst | 28 +
drivers/android/binder.c | 26 +-
fs/ceph/xattr.c | 6 +-
fs/nfs/nfs4proc.c | 8 +-
fs/nfsd/nfs4xdr.c | 20 +-
fs/proc/base.c | 2 +
include/linux/audit.h | 43 +-
include/linux/cred.h | 3 +-
include/linux/lsm_hooks.h | 36 +-
include/linux/security.h | 185 +++++-
include/net/netlabel.h | 11 +-
include/net/scm.h | 15 +-
include/net/xfrm.h | 13 +-
include/uapi/linux/audit.h | 2 +
kernel/audit.c | 175 ++++--
kernel/audit.h | 11 +-
kernel/auditfilter.c | 36 +-
kernel/auditsc.c | 191 +++---
kernel/cred.c | 12 +-
net/ipv4/cipso_ipv4.c | 26 +-
net/ipv4/ip_sockglue.c | 12 +-
net/netfilter/nf_conntrack_netlink.c | 24 +-
net/netfilter/nf_conntrack_standalone.c | 11 +-
net/netfilter/nfnetlink_queue.c | 38 +-
net/netfilter/nft_meta.c | 10 +-
net/netfilter/xt_SECMARK.c | 7 +-
net/netlabel/netlabel_domainhash.c | 4 +-
net/netlabel/netlabel_kapi.c | 6 +-
net/netlabel/netlabel_unlabeled.c | 106 ++--
net/netlabel/netlabel_unlabeled.h | 2 +-
net/netlabel/netlabel_user.c | 23 +-
net/netlabel/netlabel_user.h | 2 +-
net/xfrm/xfrm_policy.c | 10 +-
net/xfrm/xfrm_state.c | 20 +-
security/apparmor/include/apparmor.h | 3 +-
security/apparmor/include/net.h | 6 +-
security/apparmor/include/procattr.h | 2 +-
security/apparmor/lsm.c | 105 ++--
security/apparmor/procattr.c | 22 +-
security/bpf/hooks.c | 12 +-
security/commoncap.c | 7 +-
security/integrity/ima/ima.h | 15 +-
security/integrity/ima/ima_api.c | 17 +-
security/integrity/ima/ima_appraise.c | 6 +-
security/integrity/ima/ima_main.c | 54 +-
security/integrity/ima/ima_policy.c | 97 ++-
security/integrity/integrity_audit.c | 6 +-
security/loadpin/loadpin.c | 8 +-
security/lockdown/lockdown.c | 7 +-
security/safesetid/lsm.c | 8 +-
security/security.c | 561 ++++++++++++++++--
security/selinux/hooks.c | 99 ++--
security/selinux/include/classmap.h | 2 +-
security/selinux/include/objsec.h | 5 +
security/selinux/include/security.h | 1 +
security/selinux/netlabel.c | 25 +-
security/selinux/ss/services.c | 4 +-
security/smack/smack.h | 6 +
security/smack/smack_access.c | 2 +-
security/smack/smack_lsm.c | 91 +--
security/smack/smack_netfilter.c | 8 +-
security/smack/smackfs.c | 13 +-
security/tomoyo/tomoyo.c | 8 +-
security/yama/yama_lsm.c | 7 +-
67 files changed, 1741 insertions(+), 634 deletions(-)
create mode 100644 Documentation/ABI/testing/procfs-attr-context
create mode 100644 Documentation/ABI/testing/procfs-attr-lsm_display