From 5eecbc68edeb41c015d4223c4fb5fcb9b76b32b8 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian@brauner.io>
Date: Wed, 17 Apr 2019 22:50:25 +0200
Subject: [PATCH] UPSTREAM: signal: support CLONE_PIDFD with pidfd_send_signal

Let pidfd_send_signal() use pidfds retrieved via CLONE_PIDFD.  With this
patch pidfd_send_signal() becomes independent of procfs.  This fullfils
the request made when we merged the pidfd_send_signal() patchset.  The
pidfd_send_signal() syscall is now always available allowing for it to
be used by users without procfs mounted or even users without procfs
support compiled into the kernel.

Signed-off-by: Christian Brauner <christian@brauner.io>
Co-developed-by: Jann Horn <jannh@google.com>
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>

(cherry picked from commit 2151ad1b067275730de1b38c7257478cae47d29e)

Bug: 135608568
Test: test program using syscall(__NR_sys_pidfd_open,..) and poll()
Change-Id: If6ee59279f41e0ae3c6d9e24f7b5481f23aab469
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 kernel/signal.c | 12 +++++++++---
 kernel/sys_ni.c |  3 ---
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 99837647c49a..fa88d5ca566b 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3289,7 +3289,6 @@ SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
 	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
@@ -3326,6 +3325,14 @@ static int copy_siginfo_from_user_any(siginfo_t *kinfo, siginfo_t __user *info)
 	return copy_from_user(kinfo, info, sizeof(siginfo_t));
 }
 
+static struct pid *pidfd_to_pid(const struct file *file)
+{
+	if (file->f_op == &pidfd_fops)
+		return file->private_data;
+
+	return tgid_pidfd_to_pid(file);
+}
+
 /**
  * sys_pidfd_send_signal - send a signal to a process through a task file
  *                          descriptor
@@ -3362,7 +3369,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
 		return -EBADF;
 
 	/* Is this a pidfd? */
-	pid = tgid_pidfd_to_pid(f.file);
+	pid = pidfd_to_pid(f.file);
 	if (IS_ERR(pid)) {
 		ret = PTR_ERR(pid);
 		goto err;
@@ -3396,7 +3403,6 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
 	fdput(f);
 	return ret;
 }
-#endif /* CONFIG_PROC_FS */
 
 static int
 do_send_specific(pid_t tgid, pid_t pid, int sig, struct siginfo *info)
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index e0af0a166bac..70423834f116 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -162,9 +162,6 @@ COND_SYSCALL(syslog);
 
 /* kernel/sched/core.c */
 
-/* kernel/signal.c */
-COND_SYSCALL(pidfd_send_signal);
-
 /* kernel/sys.c */
 COND_SYSCALL(setregid);
 COND_SYSCALL(setgid);