Re: [PATCH v7 3/6] seccomp: add a way to get a listener fd from ptrace

 include/linux/seccomp.h                       |  7 ++
 include/uapi/linux/ptrace.h                   |  2 +
 kernel/ptrace.c                               |  4 ++
 kernel/seccomp.c                              | 31 +++++++++
 tools/testing/selftests/seccomp/seccomp_bpf.c | 68 +++++++++++++++++++
 5 files changed, 112 insertions(+)

diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 017444b5efed..234c61b37405 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h

@@ -83,6 +83,8 @@ static inline int seccomp_mode(struct seccomp *s)
 #ifdef CONFIG_SECCOMP_FILTER
 extern void put_seccomp_filter(struct task_struct *tsk);
 extern void get_seccomp_filter(struct task_struct *tsk);
+extern long seccomp_new_listener(struct task_struct *task,
+                                unsigned long filter_off);

 #else  /* CONFIG_SECCOMP_FILTER */
 static inline void put_seccomp_filter(struct task_struct *tsk)
 {

@@ -92,6 +94,11 @@ static inline void get_seccomp_filter(struct task_struct *tsk)
 {
        return;
 }
+static inline long seccomp_new_listener(struct task_struct *task,
+                                       unsigned long filter_off)
+{
+       return -EINVAL;
+}
 #endif /* CONFIG_SECCOMP_FILTER */

 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)

diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index d5a1b8a492b9..e80ecb1bd427 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_NEW_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..289960ac181b 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_NEW_LISTENER:
+               ret = seccomp_new_listener(child, addr);
+               break;
+
        default:
                break;
        }

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 44a31ac8373a..17685803a2af 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c

@@ -1777,4 +1777,35 @@ static struct file *init_listener(struct task_struct *task,

        return ret;
 }
+
+long seccomp_new_listener(struct task_struct *task,
+                         unsigned long filter_off)
+{
+       struct seccomp_filter *filter;
+       struct file *listener;
+       int fd;
+
+       if (!capable(CAP_SYS_ADMIN))
+               return -EACCES;
+
+       filter = get_nth_filter(task, filter_off);
+       if (IS_ERR(filter))
+               return PTR_ERR(filter);
+
+       fd = get_unused_fd_flags(0);

+       if (fd < 0) {
+               __put_seccomp_filter(filter);
+               return fd;
+       }
+
+       listener = init_listener(task, filter);
+       __put_seccomp_filter(filter);
+       if (IS_ERR(listener)) {
+               put_unused_fd(fd);
+               return PTR_ERR(listener);
+       }
+
+       fd_install(fd, listener);
+       return fd;
+}
 #endif

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 5f4b836a6792..c6ba3ed5392e 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c

@@ -193,6 +193,10 @@ int seccomp(unsigned int op, unsigned int flags, void *args)
 }
 #endif

+#ifndef PTRACE_SECCOMP_NEW_LISTENER
+#define PTRACE_SECCOMP_NEW_LISTENER 0x420e
+#endif
+
 #if __BYTE_ORDER == __LITTLE_ENDIAN
 #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
 #elif __BYTE_ORDER == __BIG_ENDIAN

@@ -3175,6 +3179,70 @@ TEST(get_user_notification_syscall)
        EXPECT_EQ(0, WEXITSTATUS(status));
 }

+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_NEW_LISTENER, pid, 0);
+       EXPECT_GE(listener, 0);
+
+       /* EBUSY for second listener */
+       EXPECT_EQ(ptrace(PTRACE_SECCOMP_NEW_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);
+
+       req.len = sizeof(req);
+       EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_RECV, &req), sizeof(req));
+
+       resp.len = sizeof(resp);
+       resp.id = req.id;
+       resp.error = 0;
+       resp.val = USER_NOTIF_MAGIC;
+
+       EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_SEND, &resp), sizeof(resp));
+
+       EXPECT_EQ(waitpid(pid, &status, 0), pid);
+       EXPECT_EQ(true, WIFEXITED(status));
+       EXPECT_EQ(0, WEXITSTATUS(status));
+
+       close(listener);
+}
+
 /*
  * Check that a pid in a child namespace still shows up as valid in ours.
  */
--

2.17.1