Add the current thread and thread group IDs into the data
available for seccomp-bpf programs to work on.  This allows
installation of filters that police syscalls based on thread
or process ID, e.g. tgkill(2)/kill(2)/prctl(2).

Signed-off-by: David Drysdale <redacted>
---
 include/uapi/linux/seccomp.h | 10 ++++++++++
 kernel/seccomp.c             |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
index ac2dc9f72973..b88370d6f6ca 100644
--- a/include/uapi/linux/seccomp.h
+++ b/include/uapi/linux/seccomp.h

@@ -36,12 +36,22 @@
  * @instruction_pointer: at the time of the system call.
  * @args: up to 6 system call arguments always stored as 64-bit values
  *        regardless of the architecture.
+ * @tgid: thread group ID of the thread executing the BPF program.
+ * @tid: thread ID of the thread executing the BPF program.
+ * The SECCOMP_DATA_TID_PRESENT macro indicates the presence of the
+ * tgid and tid fields; user programs may use this macro to conditionally
+ * compile code against older versions of the kernel.  Note also that
+ * BPF programs should cope with the absence of these fields by testing
+ * the length of data available.
  */
 struct seccomp_data {
        int nr;
        __u32 arch;
        __u64 instruction_pointer;
        __u64 args[6];
+       __u32 tgid;
+       __u32 tid;
 };
+#define SECCOMP_DATA_TID_PRESENT       1

 #endif /* _UAPI_LINUX_SECCOMP_H */

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 301bbc24739c..dd5146f15d6d 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c

@@ -80,6 +80,8 @@ static void populate_seccomp_data(struct seccomp_data *sd)
        sd->args[4] = args[4];
        sd->args[5] = args[5];
        sd->instruction_pointer = KSTK_EIP(task);
+       sd->tgid = task_tgid_vnr(current);
+       sd->tid = task_pid_vnr(current);
 }