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authorTyler Hicks <tyhicks@canonical.com>2017-08-11 04:33:53 +0000
committerKees Cook <keescook@chromium.org>2017-08-14 13:46:44 -0700
commitd612b1fd8010d0d67b5287fe146b8b55bcbb8655 (patch)
treecadcaeebf71ffa28aced54e9fc8b7c0ee42cc6d3
parent8e5f1ad116df6b0de65eac458d5e7c318d1c05af (diff)
seccomp: Operation for checking if an action is available
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>
-rw-r--r--include/uapi/linux/seccomp.h5
-rw-r--r--kernel/seccomp.c26
-rw-r--r--tools/testing/selftests/seccomp/seccomp_bpf.c36
3 files changed, 65 insertions, 2 deletions
diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index 0f238a43ff1e..aaad61cc46bc 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h
@@ -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
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 5f19f41e4e50..7a6089f66fed 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -808,6 +808,27 @@ static inline long seccomp_set_mode_filter(unsigned int flags,
}
#endif
+static long seccomp_get_action_avail(const char __user *uaction)
+{
+ u32 action;
+
+ if (copy_from_user(&action, uaction, sizeof(action)))
+ return -EFAULT;
+
+ switch (action) {
+ case SECCOMP_RET_KILL:
+ case SECCOMP_RET_TRAP:
+ case SECCOMP_RET_ERRNO:
+ case SECCOMP_RET_TRACE:
+ case SECCOMP_RET_ALLOW:
+ break;
+ default:
+ return -EOPNOTSUPP;
+ }
+
+ return 0;
+}
+
/* Common entry point for both prctl and syscall. */
static long do_seccomp(unsigned int op, unsigned int flags,
const char __user *uargs)
@@ -819,6 +840,11 @@ static long do_seccomp(unsigned int op, unsigned int flags,
return seccomp_set_mode_strict();
case SECCOMP_SET_MODE_FILTER:
return seccomp_set_mode_filter(flags, uargs);
+ case SECCOMP_GET_ACTION_AVAIL:
+ if (flags != 0)
+ return -EINVAL;
+
+ return seccomp_get_action_avail(uargs);
default:
return -EINVAL;
}
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 2fb49d99588d..1f2888f6678b 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1731,6 +1731,10 @@ TEST_F_SIGNAL(TRACE_syscall, kill_after_ptrace, SIGSYS)
#define SECCOMP_SET_MODE_FILTER 1
#endif
+#ifndef SECCOMP_GET_ACTION_AVAIL
+#define SECCOMP_GET_ACTION_AVAIL 2
+#endif
+
#ifndef SECCOMP_FILTER_FLAG_TSYNC
#define SECCOMP_FILTER_FLAG_TSYNC 1
#endif
@@ -2469,6 +2473,38 @@ TEST(syscall_restart)
_metadata->passed = 0;
}
+TEST(get_action_avail)
+{
+ __u32 actions[] = { SECCOMP_RET_KILL, SECCOMP_RET_TRAP,
+ SECCOMP_RET_ERRNO, SECCOMP_RET_TRACE,
+ SECCOMP_RET_ALLOW };
+ __u32 unknown_action = 0x10000000U;
+ int i;
+ long ret;
+
+ ret = seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &actions[0]);
+ ASSERT_NE(ENOSYS, errno) {
+ TH_LOG("Kernel does not support seccomp syscall!");
+ }
+ ASSERT_NE(EINVAL, errno) {
+ TH_LOG("Kernel does not support SECCOMP_GET_ACTION_AVAIL operation!");
+ }
+ EXPECT_EQ(ret, 0);
+
+ for (i = 0; i < ARRAY_SIZE(actions); i++) {
+ ret = seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &actions[i]);
+ EXPECT_EQ(ret, 0) {
+ TH_LOG("Expected action (0x%X) not available!",
+ actions[i]);
+ }
+ }
+
+ /* Check that an unknown action is handled properly (EOPNOTSUPP) */
+ ret = seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &unknown_action);
+ EXPECT_EQ(ret, -1);
+ EXPECT_EQ(errno, EOPNOTSUPP);
+}
+
/*
* TODO:
* - add microbenchmarks