Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752555AbdHKEe2 (ORCPT ); Fri, 11 Aug 2017 00:34:28 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35310 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752461AbdHKEeZ (ORCPT ); Fri, 11 Aug 2017 00:34:25 -0400 From: Tyler Hicks To: Kees Cook Cc: Andy Lutomirski , Will Drewry , Paul Moore , Eric Paris , John Crispin , Tycho Andersen , linux-audit@redhat.com, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: [PATCH v6 2/6] seccomp: Operation for checking if an action is available Date: Fri, 11 Aug 2017 04:33:53 +0000 Message-Id: <1502426037-3777-3-git-send-email-tyhicks@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1502426037-3777-1-git-send-email-tyhicks@canonical.com> References: <1502426037-3777-1-git-send-email-tyhicks@canonical.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4311 Lines: 138 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 --- include/uapi/linux/seccomp.h | 5 ++-- kernel/seccomp.c | 26 +++++++++++++++++++ tools/testing/selftests/seccomp/seccomp_bpf.c | 36 +++++++++++++++++++++++++++ 3 files changed, 65 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h index 4b75d8c..95d20d2 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 ee77eb3..1e57eff 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -854,6 +854,27 @@ 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) @@ -865,6 +886,11 @@ 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 92f2779..d3a78ec 100644 --- a/tools/testing/selftests/seccomp/seccomp_bpf.c +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c @@ -116,6 +116,10 @@ struct seccomp_data { #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 @@ -2552,6 +2556,38 @@ 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 -- 2.7.4