1 files changed, 127 insertions, 6 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 5d53183e2705..b7953934aa99 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -19,7 +19,9 @@
 #include <linux/sched/task.h>
 #include <linux/sched/task_stack.h>
 #include <linux/sched/cputime.h>
+#include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/proc_fs.h>
 #include <linux/tty.h>
 #include <linux/binfmts.h>
 #include <linux/coredump.h>
@@ -3487,6 +3489,16 @@ COMPAT_SYSCALL_DEFINE4(rt_sigtimedwait_time32, compat_sigset_t __user *, uthese,
 #endif
 #endif
 
+static inline void prepare_kill_siginfo(int sig, struct kernel_siginfo *info)
+{
+        clear_siginfo(info);
+        info->si_signo = sig;
+        info->si_errno = 0;
+        info->si_code = SI_USER;
+        info->si_pid = task_tgid_vnr(current);
+        info->si_uid = from_kuid_munged(current_user_ns(), current_uid());
+}
+
 /**
  *  sys_kill - send a signal to a process
  *  @pid: the PID of the process
@@ -3496,16 +3508,125 @@ SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
 {
         struct kernel_siginfo info;
 
-        clear_siginfo(&info);
-        info.si_signo = sig;
-        info.si_errno = 0;
-        info.si_code = SI_USER;
-        info.si_pid = task_tgid_vnr(current);
-        info.si_uid = from_kuid_munged(current_user_ns(), current_uid());
+        prepare_kill_siginfo(sig, &info);
 
         return kill_something_info(sig, &info, pid);
 }
 
+#ifdef CONFIG_PROC_FS
+/*
+ * Verify that the signaler and signalee either are in the same pid namespace
+ * or that the signaler's pid namespace is an ancestor of the signalee's pid
+ * namespace.
+ */
+static bool access_pidfd_pidns(struct pid *pid)
+{
+        struct pid_namespace *active = task_active_pid_ns(current);
+        struct pid_namespace *p = ns_of_pid(pid);
+
+        for (;;) {
+                if (!p)
+                        return false;
+                if (p == active)
+                        break;
+                p = p->parent;
+        }
+
+        return true;
+}
+
+static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo, siginfo_t *info)
+{
+#ifdef CONFIG_COMPAT
+        /*
+         * Avoid hooking up compat syscalls and instead handle necessary
+         * conversions here. Note, this is a stop-gap measure and should not be
+         * considered a generic solution.
+         */
+        if (in_compat_syscall())
+                return copy_siginfo_from_user32(
+                        kinfo, (struct compat_siginfo __user *)info);
+#endif
+        return copy_siginfo_from_user(kinfo, info);
+}
+
+/**
+ * sys_pidfd_send_signal - send a signal to a process through a task file
+ *                          descriptor
+ * @pidfd:  the file descriptor of the process
+ * @sig:    signal to be sent
+ * @info:   the signal info
+ * @flags:  future flags to be passed
+ *
+ * The syscall currently only signals via PIDTYPE_PID which covers
+ * kill(<positive-pid>, <signal>. It does not signal threads or process
+ * groups.
+ * In order to extend the syscall to threads and process groups the @flags
+ * argument should be used. In essence, the @flags argument will determine
+ * what is signaled and not the file descriptor itself. Put in other words,
+ * grouping is a property of the flags argument not a property of the file
+ * descriptor.
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
+                siginfo_t __user *, info, unsigned int, flags)
+{
+        int ret;
+        struct fd f;
+        struct pid *pid;
+        kernel_siginfo_t kinfo;
+
+        /* Enforce flags be set to 0 until we add an extension. */
+        if (flags)
+                return -EINVAL;
+
+        f = fdget_raw(pidfd);
+        if (!f.file)
+                return -EBADF;
+
+        /* Is this a pidfd? */
+        pid = tgid_pidfd_to_pid(f.file);
+        if (IS_ERR(pid)) {
+                ret = PTR_ERR(pid);
+                goto err;
+        }
+
+        ret = -EINVAL;
+        if (!access_pidfd_pidns(pid))
+                goto err;
+
+        if (info) {
+                ret = copy_siginfo_from_user_any(&kinfo, info);
+                if (unlikely(ret))
+                        goto err;
+
+                ret = -EINVAL;
+                if (unlikely(sig != kinfo.si_signo))
+                        goto err;
+
+                if ((task_pid(current) != pid) &&
+                    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)) {
+                        /* Only allow sending arbitrary signals to yourself. */
+                        ret = -EPERM;
+                        if (kinfo.si_code != SI_USER)
+                                goto err;
+
+                        /* Turn this into a regular kill signal. */
+                        prepare_kill_siginfo(sig, &kinfo);
+                }
+        } else {
+                prepare_kill_siginfo(sig, &kinfo);
+        }
+
+        ret = kill_pid_info(sig, &kinfo, pid);
+
+err:
+        fdput(f);
+        return ret;
+}
+#endif /* CONFIG_PROC_FS */
+
 static int
 do_send_specific(pid_t tgid, pid_t pid, int sig, struct kernel_siginfo *info)
 {