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seccomp: Operation for checking if an action is available

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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 <tyhicks@canonical.com>
Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Tyler Hicks
2017-08-11 04:33:53 +00:00
committed by Kees Cook
parent 8e5f1ad116
commit d612b1fd80
3 changed files with 65 additions and 2 deletions
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5
include/uapi/linux/seccomp.h
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@@ -11,8 +11,9 @@
#define SECCOMP_MODE_FILTER 2 /* uses user-supplied filter. */
/* Valid operations for seccomp syscall. */
#define SECCOMP_SET_MODE_STRICT 0
#define SECCOMP_SET_MODE_FILTER 1
#define SECCOMP_SET_MODE_STRICT 0
#define SECCOMP_SET_MODE_FILTER 1
#define SECCOMP_GET_ACTION_AVAIL 2
/* Valid flags for SECCOMP_SET_MODE_FILTER */
#define SECCOMP_FILTER_FLAG_TSYNC 1