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Biederman" , "Serge E . Hallyn" , Christian Brauner , Tyler Hicks , Akihiro Suda , "Tobin C . Harding" , Tycho Andersen Subject: [PATCH v3 3/4] seccomp: add a way to get a listener fd from ptrace Date: Thu, 31 May 2018 08:49:48 -0600 Message-Id: <20180531144949.24995-4-tycho@tycho.ws> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180531144949.24995-1-tycho@tycho.ws> References: <20180531144949.24995-1-tycho@tycho.ws> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As an alternative to SECCOMP_FILTER_FLAG_GET_LISTENER, perhaps a ptrace() version which can acquire filters is useful. There are at least two reasons this is preferable, even though it uses ptrace: 1. You can control tasks that aren't cooperating with you 2. You can control tasks whose filters block sendmsg() and socket(); if the task installs a filter which blocks these calls, there's no way with SECCOMP_FILTER_FLAG_GET_LISTENER to get the fd out to the privileged task. v2: fix a bug where listener mode was not unset when an unused fd was not available v3: fix refcounting bug (Oleg) Signed-off-by: Tycho Andersen CC: Kees Cook CC: Andy Lutomirski CC: Oleg Nesterov CC: Eric W. Biederman CC: "Serge E. Hallyn" CC: Christian Brauner CC: Tyler Hicks CC: Akihiro Suda --- include/linux/seccomp.h | 11 ++++ include/uapi/linux/ptrace.h | 2 + kernel/ptrace.c | 4 ++ kernel/seccomp.c | 28 ++++++++ tools/testing/selftests/seccomp/seccomp_bpf.c | 66 +++++++++++++++++++ 5 files changed, 111 insertions(+) diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h index 0fd3e0676a1c..10e684899b7b 100644 --- a/include/linux/seccomp.h +++ b/include/linux/seccomp.h @@ -111,4 +111,15 @@ static inline long seccomp_get_metadata(struct task_struct *task, return -EINVAL; } #endif /* CONFIG_SECCOMP_FILTER && CONFIG_CHECKPOINT_RESTORE */ + +#ifdef CONFIG_SECCOMP_USER_NOTIFICATION +extern long seccomp_get_listener(struct task_struct *task, + unsigned long filter_off); +#else +static inline long seccomp_get_listener(struct task_struct *task, + unsigned long filter_off) +{ + return -EINVAL; +} +#endif/* CONFIG_SECCOMP_USER_NOTIFICATION */ #endif /* _LINUX_SECCOMP_H */ diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h index d5a1b8a492b9..dc0abf81de3b 100644 --- a/include/uapi/linux/ptrace.h +++ b/include/uapi/linux/ptrace.h @@ -73,6 +73,8 @@ struct seccomp_metadata { __u64 flags; /* Output: filter's flags */ }; +#define PTRACE_SECCOMP_GET_LISTENER 0x420e + /* Read signals from a shared (process wide) queue */ #define PTRACE_PEEKSIGINFO_SHARED (1 << 0) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 21fec73d45d4..fcbdb6f4dc07 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -1096,6 +1096,10 @@ int ptrace_request(struct task_struct *child, long request, ret = seccomp_get_metadata(child, addr, datavp); break; + case PTRACE_SECCOMP_GET_LISTENER: + ret = seccomp_get_listener(child, addr); + break; + default: break; } diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 4a6d6bd80d07..6dc99c65c2f4 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1668,6 +1668,34 @@ static struct file *init_listener(struct task_struct *task, return ret; } + +long seccomp_get_listener(struct task_struct *task, + unsigned long filter_off) +{ + struct seccomp_filter *filter; + struct file *listener; + int fd; + + filter = get_nth_filter(task, filter_off); + if (IS_ERR(filter)) + return PTR_ERR(filter); + + fd = get_unused_fd_flags(O_RDWR); + if (fd < 0) { + __put_seccomp_filter(filter); + return fd; + } + + listener = init_listener(task, task->seccomp.filter); + __put_seccomp_filter(filter); + if (IS_ERR(listener)) { + put_unused_fd(fd); + return PTR_ERR(listener); + } + + fd_install(fd, listener); + return fd; +} #else static struct file *init_listener(struct task_struct *task, struct seccomp_filter *filter) diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c index f439bd3fb15f..07984f7bd601 100644 --- a/tools/testing/selftests/seccomp/seccomp_bpf.c +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c @@ -178,6 +178,10 @@ int seccomp(unsigned int op, unsigned int flags, void *args) } #endif +#ifndef PTRACE_SECCOMP_GET_LISTENER +#define PTRACE_SECCOMP_GET_LISTENER 0x420e +#endif + #if __BYTE_ORDER == __LITTLE_ENDIAN #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n])) #elif __BYTE_ORDER == __BIG_ENDIAN @@ -3110,6 +3114,68 @@ TEST(get_user_notification_syscall) close(listener); } +TEST(get_user_notification_ptrace) +{ + pid_t pid; + int status, listener; + int sk_pair[2]; + char c; + struct seccomp_notif req = {}; + struct seccomp_notif_resp resp = {}; + + ASSERT_EQ(socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sk_pair), 0); + + pid = fork(); + ASSERT_GE(pid, 0); + + if (pid == 0) { + EXPECT_EQ(user_trap_syscall(__NR_getpid, 0), 0); + + /* Test that we get ENOSYS while not attached */ + EXPECT_EQ(syscall(__NR_getpid), -1); + EXPECT_EQ(errno, ENOSYS); + + /* Signal we're ready and have installed the filter. */ + EXPECT_EQ(write(sk_pair[1], "J", 1), 1); + + EXPECT_EQ(read(sk_pair[1], &c, 1), 1); + EXPECT_EQ(c, 'H'); + + exit(syscall(__NR_getpid) != USER_NOTIF_MAGIC); + } + + EXPECT_EQ(read(sk_pair[0], &c, 1), 1); + EXPECT_EQ(c, 'J'); + + EXPECT_EQ(ptrace(PTRACE_ATTACH, pid), 0); + EXPECT_EQ(waitpid(pid, NULL, 0), pid); + listener = ptrace(PTRACE_SECCOMP_GET_LISTENER, pid, 0); + EXPECT_GE(listener, 0); + + /* EBUSY for second listener */ + EXPECT_EQ(ptrace(PTRACE_SECCOMP_GET_LISTENER, pid, 0), -1); + EXPECT_EQ(errno, EBUSY); + + EXPECT_EQ(ptrace(PTRACE_DETACH, pid, NULL, 0), 0); + + /* Now signal we are done and respond with magic */ + EXPECT_EQ(write(sk_pair[0], "H", 1), 1); + + EXPECT_EQ(read(listener, &req, sizeof(req)), sizeof(req)); + + resp.id = req.id; + resp.error = 0; + resp.val = USER_NOTIF_MAGIC; + + EXPECT_EQ(write(listener, &resp, sizeof(resp)), sizeof(resp)); + + EXPECT_EQ(waitpid(pid, &status, 0), pid); + EXPECT_EQ(true, WIFEXITED(status)); + EXPECT_EQ(0, WEXITSTATUS(status)); + + close(listener); +} + /* * TODO: * - add microbenchmarks -- 2.17.0