linux-toradex.git/kernel/seccomp.c, branch v4.14-rc7

seccomp: make function __get_seccomp_filter static

2017-10-10T18:45:29+00:00

The function __get_seccomp_filter is local to the source and does
not need to be in global scope, so make it static.

Cleans up sparse warning:
symbol '__get_seccomp_filter' was not declared. Should it be static?

Signed-off-by: Colin Ian King 
Fixes: 66a733ea6b61 ("seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter()")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook

seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter()

2017-09-28T05:51:12+00:00

As Chris explains, get_seccomp_filter() and put_seccomp_filter() can end
up using different filters. Once we drop ->siglock it is possible for
task->seccomp.filter to have been replaced by SECCOMP_FILTER_FLAG_TSYNC.

Fixes: f8e529ed941b ("seccomp, ptrace: add support for dumping seccomp filters")
Reported-by: Chris Salls 
Cc: stable@vger.kernel.org # needs s/refcount_/atomic_/ for v4.12 and earlier
Signed-off-by: Oleg Nesterov 
[tycho: add __get_seccomp_filter vs. open coding refcount_inc()]
Signed-off-by: Tycho Andersen 
[kees: tweak commit log]
Signed-off-by: Kees Cook

seccomp: Implement SECCOMP_RET_KILL_PROCESS action

2017-08-14T20:46:50+00:00

Right now, SECCOMP_RET_KILL_THREAD (neé SECCOMP_RET_KILL) kills the
current thread. There have been a few requests for this to kill the entire
process (the thread group). This cannot be just changed (discovered when
adding coredump support since coredumping kills the entire process)
because there are userspace programs depending on the thread-kill
behavior.

Instead, implement SECCOMP_RET_KILL_PROCESS, which is 0x80000000, and can
be processed as "-1" by the kernel, below the existing RET_KILL that is
ABI-set to "0". For userspace, SECCOMP_RET_ACTION_FULL is added to expand
the mask to the signed bit. Old userspace using the SECCOMP_RET_ACTION
mask will see SECCOMP_RET_KILL_PROCESS as 0 still, but this would only
be visible when examining the siginfo in a core dump from a RET_KILL_*,
where it will think it was thread-killed instead of process-killed.

Attempts to introduce this behavior via other ways (filter flags,
seccomp struct flags, masked RET_DATA bits) all come with weird
side-effects and baggage. This change preserves the central behavioral
expectations of the seccomp filter engine without putting too great
a burden on changes needed in userspace to use the new action.

The new action is discoverable by userspace through either the new
actions_avail sysctl or through the SECCOMP_GET_ACTION_AVAIL seccomp
operation. If used without checking for availability, old kernels
will treat RET_KILL_PROCESS as RET_KILL_THREAD (since the old mask
will produce RET_KILL_THREAD).

Cc: Paul Moore 
Cc: Fabricio Voznika 
Signed-off-by: Kees Cook

seccomp: Introduce SECCOMP_RET_KILL_PROCESS

2017-08-14T20:46:49+00:00

This introduces the BPF return value for SECCOMP_RET_KILL_PROCESS to kill
an entire process. This cannot yet be reached by seccomp, but it changes
the default-kill behavior (for unknown return values) from kill-thread to
kill-process.

Signed-off-by: Kees Cook

seccomp: Rename SECCOMP_RET_KILL to SECCOMP_RET_KILL_THREAD

2017-08-14T20:46:48+00:00

In preparation for adding SECCOMP_RET_KILL_PROCESS, rename SECCOMP_RET_KILL
to the more accurate SECCOMP_RET_KILL_THREAD.

The existing selftest values are intentionally left as SECCOMP_RET_KILL
just to be sure we're exercising the alias.

Signed-off-by: Kees Cook

seccomp: Action to log before allowing

2017-08-14T20:46:47+00:00

Add a new action, SECCOMP_RET_LOG, that logs a syscall before allowing
the syscall. At the implementation level, this action is identical to
the existing SECCOMP_RET_ALLOW action. However, it can be very useful when
initially developing a seccomp filter for an application. The developer
can set the default action to be SECCOMP_RET_LOG, maybe mark any
obviously needed syscalls with SECCOMP_RET_ALLOW, and then put the
application through its paces. A list of syscalls that triggered the
default action (SECCOMP_RET_LOG) can be easily gleaned from the logs and
that list can be used to build the syscall whitelist. Finally, the
developer can change the default action to the desired value.

This provides a more friendly experience than seeing the application get
killed, then updating the filter and rebuilding the app, seeing the
application get killed due to a different syscall, then updating the
filter and rebuilding the app, etc.

The functionality is similar to what's supported by the various LSMs.
SELinux has permissive mode, AppArmor has complain mode, SMACK has
bring-up mode, etc.

SECCOMP_RET_LOG is given a lower value than SECCOMP_RET_ALLOW as allow
while logging is slightly more restrictive than quietly allowing.

Unfortunately, the tests added for SECCOMP_RET_LOG are not capable of
inspecting the audit log to verify that the syscall was logged.

With this patch, the logic for deciding if an action will be logged is:

if action == RET_ALLOW:
  do not log
else if action == RET_KILL && RET_KILL in actions_logged:
  log
else if action == RET_LOG && RET_LOG in actions_logged:
  log
else if filter-requests-logging && action in actions_logged:
  log
else if audit_enabled && process-is-being-audited:
  log
else:
  do not log

Signed-off-by: Tyler Hicks 
Signed-off-by: Kees Cook

seccomp: Filter flag to log all actions except SECCOMP_RET_ALLOW

2017-08-14T20:46:46+00:00

Add a new filter flag, SECCOMP_FILTER_FLAG_LOG, that enables logging for
all actions except for SECCOMP_RET_ALLOW for the given filter.

SECCOMP_RET_KILL actions are always logged, when "kill" is in the
actions_logged sysctl, and SECCOMP_RET_ALLOW actions are never logged,
regardless of this flag.

This flag can be used to create noisy filters that result in all
non-allowed actions to be logged. A process may have one noisy filter,
which is loaded with this flag, as well as a quiet filter that's not
loaded with this flag. This allows for the actions in a set of filters
to be selectively conveyed to the admin.

Since a system could have a large number of allocated seccomp_filter
structs, struct packing was taken in consideration. On 64 bit x86, the
new log member takes up one byte of an existing four byte hole in the
struct. On 32 bit x86, the new log member creates a new four byte hole
(unavoidable) and consumes one of those bytes.

Unfortunately, the tests added for SECCOMP_FILTER_FLAG_LOG are not
capable of inspecting the audit log to verify that the actions taken in
the filter were logged.

With this patch, the logic for deciding if an action will be logged is:

if action == RET_ALLOW:
  do not log
else if action == RET_KILL && RET_KILL in actions_logged:
  log
else if filter-requests-logging && action in actions_logged:
  log
else if audit_enabled && process-is-being-audited:
  log
else:
  do not log

Signed-off-by: Tyler Hicks 
Signed-off-by: Kees Cook

seccomp: Sysctl to configure actions that are allowed to be logged

2017-08-14T20:46:45+00:00

Adminstrators can write to this sysctl to set the seccomp actions that
are allowed to be logged. Any actions not found in this sysctl will not
be logged.

For example, all SECCOMP_RET_KILL, SECCOMP_RET_TRAP, and
SECCOMP_RET_ERRNO actions would be loggable if "kill trap errno" were
written to the sysctl. SECCOMP_RET_TRACE actions would not be logged
since its string representation ("trace") wasn't present in the sysctl
value.

The path to the sysctl is:

 /proc/sys/kernel/seccomp/actions_logged

The actions_avail sysctl can be read to discover the valid action names
that can be written to the actions_logged sysctl with the exception of
"allow". SECCOMP_RET_ALLOW actions cannot be configured for logging.

The default setting for the sysctl is to allow all actions to be logged
except SECCOMP_RET_ALLOW. While only SECCOMP_RET_KILL actions are
currently logged, an upcoming patch will allow applications to request
additional actions to be logged.

There's one important exception to this sysctl. If a task is
specifically being audited, meaning that an audit context has been
allocated for the task, seccomp will log all actions other than
SECCOMP_RET_ALLOW despite the value of actions_logged. This exception
preserves the existing auditing behavior of tasks with an allocated
audit context.

With this patch, the logic for deciding if an action will be logged is:

if action == RET_ALLOW:
  do not log
else if action == RET_KILL && RET_KILL in actions_logged:
  log
else if audit_enabled && task-is-being-audited:
  log
else:
  do not log

Signed-off-by: Tyler Hicks 
Signed-off-by: Kees Cook

seccomp: Operation for checking if an action is available

2017-08-14T20:46:44+00:00

Userspace code that needs to check if the kernel supports a given action
may not be able to use the /proc/sys/kernel/seccomp/actions_avail
sysctl. The process may be running in a sandbox and, therefore,
sufficient filesystem access may not be available. This patch adds an
operation to the seccomp(2) syscall that allows userspace code to ask
the kernel if a given action is available.

If the action is supported by the kernel, 0 is returned. If the action
is not supported by the kernel, -1 is returned with errno set to
-EOPNOTSUPP. If this check is attempted on a kernel that doesn't support
this new operation, -1 is returned with errno set to -EINVAL meaning
that userspace code will have the ability to differentiate between the
two error cases.

Signed-off-by: Tyler Hicks 
Suggested-by: Andy Lutomirski 
Signed-off-by: Kees Cook

seccomp: Sysctl to display available actions

2017-08-14T20:46:43+00:00

This patch creates a read-only sysctl containing an ordered list of
seccomp actions that the kernel supports. The ordering, from left to
right, is the lowest action value (kill) to the highest action value
(allow). Currently, a read of the sysctl file would return "kill trap
errno trace allow". The contents of this sysctl file can be useful for
userspace code as well as the system administrator.

The path to the sysctl is:

  /proc/sys/kernel/seccomp/actions_avail

libseccomp and other userspace code can easily determine which actions
the current kernel supports. The set of actions supported by the current
kernel may be different than the set of action macros found in kernel
headers that were installed where the userspace code was built.

In addition, this sysctl will allow system administrators to know which
actions are supported by the kernel and make it easier to configure
exactly what seccomp logs through the audit subsystem. Support for this
level of logging configuration will come in a future patch.

Signed-off-by: Tyler Hicks 
Signed-off-by: Kees Cook