On Thu, May 17, 2018 at 09:12:17AM -0600, Tycho Andersen wrote: > 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.
I get the problem I guess the question we need to answer is do we care enought to bring ptrace into this? Not really objecting, just asking. :) If blocking sendmsg() or socket() becomes an issue because people like to shoot themselves in the foot we can surely add this option later. Christian > > v2: fix a bug where listener mode was not unset when an unused fd was not > available > > Signed-off-by: Tycho Andersen <[email protected]> > CC: Kees Cook <[email protected]> > CC: Andy Lutomirski <[email protected]> > CC: Oleg Nesterov <[email protected]> > CC: Eric W. Biederman <[email protected]> > CC: "Serge E. Hallyn" <[email protected]> > CC: Christian Brauner <[email protected]> > CC: Tyler Hicks <[email protected]> > CC: Akihiro Suda <[email protected]> > --- > include/linux/seccomp.h | 11 ++++ > include/uapi/linux/ptrace.h | 2 + > kernel/ptrace.c | 4 ++ > kernel/seccomp.c | 27 ++++++++ > tools/testing/selftests/seccomp/seccomp_bpf.c | 66 +++++++++++++++++++ > 5 files changed, 110 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 f136eca93f2f..7c23aee76bb4 100644 > --- a/kernel/seccomp.c > +++ b/kernel/seccomp.c > @@ -1678,4 +1678,31 @@ 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); > + 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 bb96df66222f..473905f33e0b 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 > @@ -3096,6 +3100,68 @@ 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 > > _______________________________________________ > Containers mailing list > [email protected] > https://lists.linuxfoundation.org/mailman/listinfo/containers
