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  1. 23 5月, 2022 1 次提交
  3. 14 5月, 2022 1 次提交
  5. 16 2月, 2022 1 次提交
  7. 07 12月, 2021 1 次提交
  9. 23 11月, 2021 1 次提交
  11. 14 11月, 2021 1 次提交
    • P
      net,lsm,selinux: revert the security_sctp_assoc_established() hook · 1aa3b220
      由 Paul Moore 提交于 
      This patch reverts two prior patches, e7310c94
("security: implement sctp_assoc_established hook in selinux") and
7c2ef024 ("security: add sctp_assoc_established hook"), which
create the security_sctp_assoc_established() LSM hook and provide a
SELinux implementation.  Unfortunately these two patches were merged
without proper review (the Reviewed-by and Tested-by tags from
Richard Haines were for previous revisions of these patches that
were significantly different) and there are outstanding objections
from the SELinux maintainers regarding these patches.

Work is currently ongoing to correct the problems identified in the
reverted patches, as well as others that have come up during review,
but it is unclear at this point in time when that work will be ready
for inclusion in the mainline kernel.  In the interest of not keeping
objectionable code in the kernel for multiple weeks, and potentially
a kernel release, we are reverting the two problematic patches.
Signed-off-by: NPaul Moore <paul@paul-moore.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      1aa3b220
  13. 13 11月, 2021 1 次提交
    • P
      net,lsm,selinux: revert the security_sctp_assoc_established() hook · 32a370ab
      由 Paul Moore 提交于 
      This patch reverts two prior patches, e7310c94
("security: implement sctp_assoc_established hook in selinux") and
7c2ef024 ("security: add sctp_assoc_established hook"), which
create the security_sctp_assoc_established() LSM hook and provide a
SELinux implementation.  Unfortunately these two patches were merged
without proper review (the Reviewed-by and Tested-by tags from
Richard Haines were for previous revisions of these patches that
were significantly different) and there are outstanding objections
from the SELinux maintainers regarding these patches.

Work is currently ongoing to correct the problems identified in the
reverted patches, as well as others that have come up during review,
but it is unclear at this point in time when that work will be ready
for inclusion in the mainline kernel.  In the interest of not keeping
objectionable code in the kernel for multiple weeks, and potentially
a kernel release, we are reverting the two problematic patches.
Signed-off-by: NPaul Moore <paul@paul-moore.com>
      32a370ab
  15. 03 11月, 2021 2 次提交
  17. 20 10月, 2021 1 次提交
  19. 15 10月, 2021 1 次提交
  21. 20 9月, 2021 1 次提交
    • P
      lsm,io_uring: add LSM hooks to io_uring · cdc1404a
      由 Paul Moore 提交于 
      A full expalantion of io_uring is beyond the scope of this commit
description, but in summary it is an asynchronous I/O mechanism
which allows for I/O requests and the resulting data to be queued
in memory mapped "rings" which are shared between the kernel and
userspace.  Optionally, io_uring offers the ability for applications
to spawn kernel threads to dequeue I/O requests from the ring and
submit the requests in the kernel, helping to minimize the syscall
overhead.  Rings are accessed in userspace by memory mapping a file
descriptor provided by the io_uring_setup(2), and can be shared
between applications as one might do with any open file descriptor.
Finally, process credentials can be registered with a given ring
and any process with access to that ring can submit I/O requests
using any of the registered credentials.

While the io_uring functionality is widely recognized as offering a
vastly improved, and high performing asynchronous I/O mechanism, its
ability to allow processes to submit I/O requests with credentials
other than its own presents a challenge to LSMs.  When a process
creates a new io_uring ring the ring's credentials are inhertied
from the calling process; if this ring is shared with another
process operating with different credentials there is the potential
to bypass the LSMs security policy.  Similarly, registering
credentials with a given ring allows any process with access to that
ring to submit I/O requests with those credentials.

In an effort to allow LSMs to apply security policy to io_uring I/O
operations, this patch adds two new LSM hooks.  These hooks, in
conjunction with the LSM anonymous inode support previously
submitted, allow an LSM to apply access control policy to the
sharing of io_uring rings as well as any io_uring credential changes
requested by a process.

The new LSM hooks are described below:

 * int security_uring_override_creds(cred)
   Controls if the current task, executing an io_uring operation,
   is allowed to override it's credentials with @cred.  In cases
   where the current task is a user application, the current
   credentials will be those of the user application.  In cases
   where the current task is a kernel thread servicing io_uring
   requests the current credentials will be those of the io_uring
   ring (inherited from the process that created the ring).

 * int security_uring_sqpoll(void)
   Controls if the current task is allowed to create an io_uring
   polling thread (IORING_SETUP_SQPOLL).  Without a SQPOLL thread
   in the kernel processes must submit I/O requests via
   io_uring_enter(2) which allows us to compare any requested
   credential changes against the application making the request.
   With a SQPOLL thread, we can no longer compare requested
   credential changes against the application making the request,
   the comparison is made against the ring's credentials.
Signed-off-by: NPaul Moore <paul@paul-moore.com>
      cdc1404a
  23. 23 4月, 2021 2 次提交
  25. 23 3月, 2021 2 次提交
    • P
      lsm: separate security_task_getsecid() into subjective and objective variants · 4ebd7651
      由 Paul Moore 提交于 
      Of the three LSMs that implement the security_task_getsecid() LSM
hook, all three LSMs provide the task's objective security
credentials.  This turns out to be unfortunate as most of the hook's
callers seem to expect the task's subjective credentials, although
a small handful of callers do correctly expect the objective
credentials.

This patch is the first step towards fixing the problem: it splits
the existing security_task_getsecid() hook into two variants, one
for the subjective creds, one for the objective creds.

  void security_task_getsecid_subj(struct task_struct *p,
				   u32 *secid);
  void security_task_getsecid_obj(struct task_struct *p,
				  u32 *secid);

While this patch does fix all of the callers to use the correct
variant, in order to keep this patch focused on the callers and to
ease review, the LSMs continue to use the same implementation for
both hooks.  The net effect is that this patch should not change
the behavior of the kernel in any way, it will be up to the latter
LSM specific patches in this series to change the hook
implementations and return the correct credentials.

Acked-by: Mimi Zohar <zohar@linux.ibm.com> (IMA)
Acked-by: NCasey Schaufler <casey@schaufler-ca.com>
Reviewed-by: NRichard Guy Briggs <rgb@redhat.com>
Signed-off-by: NPaul Moore <paul@paul-moore.com>
      4ebd7651
    • O
      lsm,selinux: add new hook to compare new mount to an existing mount · 69c4a42d
      由 Olga Kornievskaia 提交于 
      Add a new hook that takes an existing super block and a new mount
with new options and determines if new options confict with an
existing mount or not.

A filesystem can use this new hook to determine if it can share
the an existing superblock with a new superblock for the new mount.
Signed-off-by: NOlga Kornievskaia <kolga@netapp.com>
Acked-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>
[PM: tweak the subject line, fix tab/space problems]
Signed-off-by: NPaul Moore <paul@paul-moore.com>
      69c4a42d
  27. 24 1月, 2021 1 次提交
    • C
      commoncap: handle idmapped mounts · 71bc356f
      由 Christian Brauner 提交于 
      When interacting with user namespace and non-user namespace aware
filesystem capabilities the vfs will perform various security checks to
determine whether or not the filesystem capabilities can be used by the
caller, whether they need to be removed and so on. The main
infrastructure for this resides in the capability codepaths but they are
called through the LSM security infrastructure even though they are not
technically an LSM or optional. This extends the existing security hooks
security_inode_removexattr(), security_inode_killpriv(),
security_inode_getsecurity() to pass down the mount's user namespace and
makes them aware of idmapped mounts.

In order to actually get filesystem capabilities from disk the
capability infrastructure exposes the get_vfs_caps_from_disk() helper.
For user namespace aware filesystem capabilities a root uid is stored
alongside the capabilities.

In order to determine whether the caller can make use of the filesystem
capability or whether it needs to be ignored it is translated according
to the superblock's user namespace. If it can be translated to uid 0
according to that id mapping the caller can use the filesystem
capabilities stored on disk. If we are accessing the inode that holds
the filesystem capabilities through an idmapped mount we map the root
uid according to the mount's user namespace. Afterwards the checks are
identical to non-idmapped mounts: reading filesystem caps from disk
enforces that the root uid associated with the filesystem capability
must have a mapping in the superblock's user namespace and that the
caller is either in the same user namespace or is a descendant of the
superblock's user namespace. For filesystems that are mountable inside
user namespace the caller can just mount the filesystem and won't
usually need to idmap it. If they do want to idmap it they can create an
idmapped mount and mark it with a user namespace they created and which
is thus a descendant of s_user_ns. For filesystems that are not
mountable inside user namespaces the descendant rule is trivially true
because the s_user_ns will be the initial user namespace.

If the initial user namespace is passed nothing changes so non-idmapped
mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-11-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NJames Morris <jamorris@linux.microsoft.com>
Signed-off-by: NChristian Brauner <christian.brauner@ubuntu.com>
      71bc356f
  29. 15 1月, 2021 1 次提交
    • L
      security: add inode_init_security_anon() LSM hook · 215b674b
      由 Lokesh Gidra 提交于 
      This change adds a new LSM hook, inode_init_security_anon(), that will
be used while creating secure anonymous inodes. The hook allows/denies
its creation and assigns a security context to the inode.

The new hook accepts an optional context_inode parameter that callers
can use to provide additional contextual information to security modules
for granting/denying permission to create an anon-inode of the same type.
This context_inode's security_context can also be used to initialize the
newly created anon-inode's security_context.
Signed-off-by: NLokesh Gidra <lokeshgidra@google.com>
Reviewed-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NPaul Moore <paul@paul-moore.com>
      215b674b
  31. 24 11月, 2020 1 次提交
  33. 26 10月, 2020 1 次提交
  35. 05 10月, 2020 2 次提交
    • K
      LSM: Add "contents" flag to kernel_read_file hook · 2039bda1
      由 Kees Cook 提交于 
      As with the kernel_load_data LSM hook, add a "contents" flag to the
kernel_read_file LSM hook that indicates whether the LSM can expect
a matching call to the kernel_post_read_file LSM hook with the full
contents of the file. With the coming addition of partial file read
support for kernel_read_file*() API, the LSM will no longer be able
to always see the entire contents of a file during the read calls.

For cases where the LSM must read examine the complete file contents,
it will need to do so on its own every time the kernel_read_file
hook is called with contents=false (or reject such cases). Adjust all
existing LSMs to retain existing behavior.
Signed-off-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NMimi Zohar <zohar@linux.ibm.com>
Link: https://lore.kernel.org/r/20201002173828.2099543-12-keescook@chromium.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      2039bda1
    • K
      LSM: Introduce kernel_post_load_data() hook · b64fcae7
      由 Kees Cook 提交于 
      There are a few places in the kernel where LSMs would like to have
visibility into the contents of a kernel buffer that has been loaded or
read. While security_kernel_post_read_file() (which includes the
buffer) exists as a pairing for security_kernel_read_file(), no such
hook exists to pair with security_kernel_load_data().

Earlier proposals for just using security_kernel_post_read_file() with a
NULL file argument were rejected (i.e. "file" should always be valid for
the security_..._file hooks, but it appears at least one case was
left in the kernel during earlier refactoring. (This will be fixed in
a subsequent patch.)

Since not all cases of security_kernel_load_data() can have a single
contiguous buffer made available to the LSM hook (e.g. kexec image
segments are separately loaded), there needs to be a way for the LSM to
reason about its expectations of the hook coverage. In order to handle
this, add a "contents" argument to the "kernel_load_data" hook that
indicates if the newly added "kernel_post_load_data" hook will be called
with the full contents once loaded. That way, LSMs requiring full contents
can choose to unilaterally reject "kernel_load_data" with contents=false
(which is effectively the existing hook coverage), but when contents=true
they can allow it and later evaluate the "kernel_post_load_data" hook
once the buffer is loaded.

With this change, LSMs can gain coverage over non-file-backed data loads
(e.g. init_module(2) and firmware userspace helper), which will happen
in subsequent patches.

Additionally prepare IMA to start processing these cases.
Signed-off-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NKP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/r/20201002173828.2099543-9-keescook@chromium.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      b64fcae7
  37. 07 8月, 2020 1 次提交
  39. 15 6月, 2020 1 次提交
  41. 30 5月, 2020 2 次提交
    • E
      exec: Compute file based creds only once · 56305aa9
      由 Eric W. Biederman 提交于 
      Move the computation of creds from prepare_binfmt into begin_new_exec
so that the creds need only be computed once.  This is just code
reorganization no semantic changes of any kind are made.

Moving the computation is safe.  I have looked through the kernel and
verified none of the binfmts look at bprm->cred directly, and that
there are no helpers that look at bprm->cred indirectly.  Which means
that it is not a problem to compute the bprm->cred later in the
execution flow as it is not used until it becomes current->cred.

A new function bprm_creds_from_file is added to contain the work that
needs to be done.  bprm_creds_from_file first computes which file
bprm->executable or most likely bprm->file that the bprm->creds
will be computed from.

The funciton bprm_fill_uid is updated to receive the file instead of
accessing bprm->file.  The now unnecessary work needed to reset the
bprm->cred->euid, and bprm->cred->egid is removed from brpm_fill_uid.
A small comment to document that bprm_fill_uid now only deals with the
work to handle suid and sgid files.  The default case is already
heandled by prepare_exec_creds.

The function security_bprm_repopulate_creds is renamed
security_bprm_creds_from_file and now is explicitly passed the file
from which to compute the creds.  The documentation of the
bprm_creds_from_file security hook is updated to explain when the hook
is called and what it needs to do.  The file is passed from
cap_bprm_creds_from_file into get_file_caps so that the caps are
computed for the appropriate file.  The now unnecessary work in
cap_bprm_creds_from_file to reset the ambient capabilites has been
removed.  A small comment to document that the work of
cap_bprm_creds_from_file is to read capabilities from the files
secureity attribute and derive capabilities from the fact the
user had uid 0 has been added.
Reviewed-by: NKees Cook <keescook@chromium.org>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      56305aa9
    • E
      exec: Add a per bprm->file version of per_clear · a7868323
      由 Eric W. Biederman 提交于 
      There is a small bug in the code that recomputes parts of bprm->cred
for every bprm->file.  The code never recomputes the part of
clear_dangerous_personality_flags it is responsible for.

Which means that in practice if someone creates a sgid script
the interpreter will not be able to use any of:
	READ_IMPLIES_EXEC
	ADDR_NO_RANDOMIZE
	ADDR_COMPAT_LAYOUT
	MMAP_PAGE_ZERO.

This accentially clearing of personality flags probably does
not matter in practice because no one has complained
but it does make the code more difficult to understand.

Further remaining bug compatible prevents the recomputation from being
removed and replaced by simply computing bprm->cred once from the
final bprm->file.

Making this change removes the last behavior difference between
computing bprm->creds from the final file and recomputing
bprm->cred several times.  Which allows this behavior change
to be justified for it's own reasons, and for any but hunts
looking into why the behavior changed to wind up here instead
of in the code that will follow that computes bprm->cred
from the final bprm->file.

This small logic bug appears to have existed since the code
started clearing dangerous personality bits.

History Tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: 1bb0fa189c6a ("[PATCH] NX: clean up legacy binary support")
Reviewed-by: NKees Cook <keescook@chromium.org>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      a7868323
  43. 21 5月, 2020 2 次提交
  45. 19 5月, 2020 2 次提交
  47. 05 5月, 2020 1 次提交
  49. 30 3月, 2020 1 次提交
  51. 20 2月, 2020 1 次提交
    • R
      security: <linux/lsm_hooks.h>: fix all kernel-doc warnings · bd1a5a53
      由 Randy Dunlap 提交于 
      Fix all kernel-doc warnings in <linux/lsm_hooks.h>.
Fixes the following warnings:

../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'quotactl' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'quota_on' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'sb_free_mnt_opts' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'sb_eat_lsm_opts' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'sb_kern_mount' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'sb_show_options' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'sb_add_mnt_opt' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'd_instantiate' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'getprocattr' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'setprocattr' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'locked_down' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'perf_event_open' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'perf_event_alloc' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'perf_event_free' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'perf_event_read' not described in 'security_list_options'
../include/linux/lsm_hooks.h:1830: warning: Function parameter or member 'perf_event_write' not described in 'security_list_options'
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Cc: John Johansen <john.johansen@canonical.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Micah Morton <mortonm@chromium.org>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Kentaro Takeda <takedakn@nttdata.co.jp>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: NCasey Schaufler <casey@schaufler-ca.com>
Acked-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NJames Morris <jmorris@namei.org>
      bd1a5a53
  53. 18 10月, 2019 1 次提交
    • J
      perf_event: Add support for LSM and SELinux checks · da97e184
      由 Joel Fernandes (Google) 提交于 
      In current mainline, the degree of access to perf_event_open(2) system
call depends on the perf_event_paranoid sysctl.  This has a number of
limitations:

1. The sysctl is only a single value. Many types of accesses are controlled
   based on the single value thus making the control very limited and
   coarse grained.
2. The sysctl is global, so if the sysctl is changed, then that means
   all processes get access to perf_event_open(2) opening the door to
   security issues.

This patch adds LSM and SELinux access checking which will be used in
Android to access perf_event_open(2) for the purposes of attaching BPF
programs to tracepoints, perf profiling and other operations from
userspace. These operations are intended for production systems.

5 new LSM hooks are added:
1. perf_event_open: This controls access during the perf_event_open(2)
   syscall itself. The hook is called from all the places that the
   perf_event_paranoid sysctl is checked to keep it consistent with the
   systctl. The hook gets passed a 'type' argument which controls CPU,
   kernel and tracepoint accesses (in this context, CPU, kernel and
   tracepoint have the same semantics as the perf_event_paranoid sysctl).
   Additionally, I added an 'open' type which is similar to
   perf_event_paranoid sysctl == 3 patch carried in Android and several other
   distros but was rejected in mainline [1] in 2016.

2. perf_event_alloc: This allocates a new security object for the event
   which stores the current SID within the event. It will be useful when
   the perf event's FD is passed through IPC to another process which may
   try to read the FD. Appropriate security checks will limit access.

3. perf_event_free: Called when the event is closed.

4. perf_event_read: Called from the read(2) and mmap(2) syscalls for the event.

5. perf_event_write: Called from the ioctl(2) syscalls for the event.

[1] https://lwn.net/Articles/696240/

Since Peter had suggest LSM hooks in 2016 [1], I am adding his
Suggested-by tag below.

To use this patch, we set the perf_event_paranoid sysctl to -1 and then
apply selinux checking as appropriate (default deny everything, and then
add policy rules to give access to domains that need it). In the future
we can remove the perf_event_paranoid sysctl altogether.
Suggested-by: NPeter Zijlstra <peterz@infradead.org>
Co-developed-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NJames Morris <jmorris@namei.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: rostedt@goodmis.org
Cc: Yonghong Song <yhs@fb.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: jeffv@google.com
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: primiano@google.com
Cc: Song Liu <songliubraving@fb.com>
Cc: rsavitski@google.com
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Matthew Garrett <matthewgarrett@google.com>
Link: https://lkml.kernel.org/r/20191014170308.70668-1-joel@joelfernandes.org
      da97e184
  55. 20 8月, 2019 2 次提交
  57. 13 8月, 2019 1 次提交
    • A
      fanotify, inotify, dnotify, security: add security hook for fs notifications · ac5656d8
      由 Aaron Goidel 提交于 
      As of now, setting watches on filesystem objects has, at most, applied a
check for read access to the inode, and in the case of fanotify, requires
CAP_SYS_ADMIN. No specific security hook or permission check has been
provided to control the setting of watches. Using any of inotify, dnotify,
or fanotify, it is possible to observe, not only write-like operations, but
even read access to a file. Modeling the watch as being merely a read from
the file is insufficient for the needs of SELinux. This is due to the fact
that read access should not necessarily imply access to information about
when another process reads from a file. Furthermore, fanotify watches grant
more power to an application in the form of permission events. While
notification events are solely, unidirectional (i.e. they only pass
information to the receiving application), permission events are blocking.
Permission events make a request to the receiving application which will
then reply with a decision as to whether or not that action may be
completed. This causes the issue of the watching application having the
ability to exercise control over the triggering process. Without drawing a
distinction within the permission check, the ability to read would imply
the greater ability to control an application. Additionally, mount and
superblock watches apply to all files within the same mount or superblock.
Read access to one file should not necessarily imply the ability to watch
all files accessed within a given mount or superblock.

In order to solve these issues, a new LSM hook is implemented and has been
placed within the system calls for marking filesystem objects with inotify,
fanotify, and dnotify watches. These calls to the hook are placed at the
point at which the target path has been resolved and are provided with the
path struct, the mask of requested notification events, and the type of
object on which the mark is being set (inode, superblock, or mount). The
mask and obj_type have already been translated into common FS_* values
shared by the entirety of the fs notification infrastructure. The path
struct is passed rather than just the inode so that the mount is available,
particularly for mount watches. This also allows for use of the hook by
pathname-based security modules. However, since the hook is intended for
use even by inode based security modules, it is not placed under the
CONFIG_SECURITY_PATH conditional. Otherwise, the inode-based security
modules would need to enable all of the path hooks, even though they do not
use any of them.

This only provides a hook at the point of setting a watch, and presumes
that permission to set a particular watch implies the ability to receive
all notification about that object which match the mask. This is all that
is required for SELinux. If other security modules require additional hooks
or infrastructure to control delivery of notification, these can be added
by them. It does not make sense for us to propose hooks for which we have
no implementation. The understanding that all notifications received by the
requesting application are all strictly of a type for which the application
has been granted permission shows that this implementation is sufficient in
its coverage.

Security modules wishing to provide complete control over fanotify must
also implement a security_file_open hook that validates that the access
requested by the watching application is authorized. Fanotify has the issue
that it returns a file descriptor with the file mode specified during
fanotify_init() to the watching process on event. This is already covered
by the LSM security_file_open hook if the security module implements
checking of the requested file mode there. Otherwise, a watching process
can obtain escalated access to a file for which it has not been authorized.

The selinux_path_notify hook implementation works by adding five new file
permissions: watch, watch_mount, watch_sb, watch_reads, and watch_with_perm
(descriptions about which will follow), and one new filesystem permission:
watch (which is applied to superblock checks). The hook then decides which
subset of these permissions must be held by the requesting application
based on the contents of the provided mask and the obj_type. The
selinux_file_open hook already checks the requested file mode and therefore
ensures that a watching process cannot escalate its access through
fanotify.

The watch, watch_mount, and watch_sb permissions are the baseline
permissions for setting a watch on an object and each are a requirement for
any watch to be set on a file, mount, or superblock respectively. It should
be noted that having either of the other two permissions (watch_reads and
watch_with_perm) does not imply the watch, watch_mount, or watch_sb
permission. Superblock watches further require the filesystem watch
permission to the superblock. As there is no labeled object in view for
mounts, there is no specific check for mount watches beyond watch_mount to
the inode. Such a check could be added in the future, if a suitable labeled
object existed representing the mount.

The watch_reads permission is required to receive notifications from
read-exclusive events on filesystem objects. These events include accessing
a file for the purpose of reading and closing a file which has been opened
read-only. This distinction has been drawn in order to provide a direct
indication in the policy for this otherwise not obvious capability. Read
access to a file should not necessarily imply the ability to observe read
events on a file.

Finally, watch_with_perm only applies to fanotify masks since it is the
only way to set a mask which allows for the blocking, permission event.
This permission is needed for any watch which is of this type. Though
fanotify requires CAP_SYS_ADMIN, this is insufficient as it gives implicit
trust to root, which we do not do, and does not support least privilege.
Signed-off-by: NAaron Goidel <acgoide@tycho.nsa.gov>
Acked-by: NCasey Schaufler <casey@schaufler-ca.com>
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NPaul Moore <paul@paul-moore.com>
      ac5656d8
  59. 09 6月, 2019 1 次提交
  61. 27 3月, 2019 2 次提交