From 08583d5ad48528261678df724deb0978d98a7b81 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Mon, 18 Sep 2023 07:19:53 +0200
Subject: [PATCH] kernel: Allow sending signals to process groups from
 userspace

---
 kernel/src/sys/signal.cpp | 65 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 8 deletions(-)

diff --git a/kernel/src/sys/signal.cpp b/kernel/src/sys/signal.cpp
index 779b151c..2d2d05c9 100644
--- a/kernel/src/sys/signal.cpp
+++ b/kernel/src/sys/signal.cpp
@@ -54,16 +54,65 @@ Result<u64> sys_kill(Registers*, SyscallArgs args)
     pid_t pid = (pid_t)args[0];
     int signo = (int)args[1];
 
-    // FIXME: Support this case.
-    if (pid <= 0) return err(ENOTSUP);
+    auto send_signal = [&](Thread* target) -> Result<void> {
+        if (current->auth.euid != 0 && current->auth.euid != target->auth.euid &&
+            current->auth.egid != target->auth.egid)
+            return err(EPERM);
+        if (target->is_kernel) return {};
+        if (signo == 0) return {};
 
-    auto* target = TRY(Result<Thread*>::from_option(Scheduler::find_by_pid(pid), ESRCH));
-    if (current->auth.euid != 0 && current->auth.euid != target->auth.euid && current->auth.egid != target->auth.egid)
-        return err(EPERM);
-    if (target->is_kernel) return 0;
-    if (signo == 0) return 0;
+        target->send_signal(signo);
 
-    target->send_signal(signo);
+        return {};
+    };
+
+    if (pid > 0)
+    {
+        auto* target = TRY(Result<Thread*>::from_option(Scheduler::find_by_pid(pid), ESRCH));
+        TRY(send_signal(target));
+    }
+    else if (pid == 0)
+    {
+        int errno = -1;
+        bool pgid_exists = false;
+        Scheduler::for_each_in_process_group(current->pgid, [&](Thread* target) {
+            pgid_exists = true;
+            auto rc = send_signal(target);
+            if (rc.has_error())
+            {
+                errno = rc.error();
+                return false;
+            }
+            return true;
+        });
+        if (errno > 0) return err(errno);
+        if (!pgid_exists) return err(ESRCH);
+    }
+    else if (pid == -1)
+    {
+        for (auto* thread : g_threads)
+        {
+            // We ignore permission errors here.
+            if (thread != current && thread->id != 1) send_signal(thread);
+        }
+    }
+    else if (pid < -1)
+    {
+        int errno = -1;
+        bool pgid_exists = false;
+        Scheduler::for_each_in_process_group(-pid, [&](Thread* target) {
+            pgid_exists = true;
+            auto rc = send_signal(target);
+            if (rc.has_error())
+            {
+                errno = rc.error();
+                return false;
+            }
+            return true;
+        });
+        if (errno > 0) return err(errno);
+        if (!pgid_exists) return err(ESRCH);
+    }
 
     return 0;
 }