Subject: Re: Coverity: __do_sys_pidfd_send_signal(): UNINIT

From: Oleg Nesterov <[email-masked]>
Date: Wed, 14 Feb 2024 10:03:33 +0100

On 02/13, Tycho Andersen wrote:
>
> I think this is a false positive, we have:

Agreed,

> That said, a default case wouldn't hurt, and we should fix the first
> comment anyways, since now we have extensions.
>
> I'm happy to send a patch or maybe it's better for Christian to fix it
> in-tree.

I leave this to you and Christian, whatever you prefer. But perhaps we
can simplify these checks? Something like below.

Oleg.

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3876,10 +3876,6 @@ static struct pid *pidfd_to_pid(const struct file *file)
 	return tgid_pidfd_to_pid(file);
 }
 
-#define PIDFD_SEND_SIGNAL_FLAGS                            \
-	(PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \
-	 PIDFD_SIGNAL_PROCESS_GROUP)
-
 /**
  * sys_pidfd_send_signal - Signal a process through a pidfd
  * @pidfd:  file descriptor of the process
@@ -3903,13 +3899,21 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
 	kernel_siginfo_t kinfo;
 	enum pid_type type;
 
-	/* Enforce flags be set to 0 until we add an extension. */
-	if (flags & ~PIDFD_SEND_SIGNAL_FLAGS)
-		return -EINVAL;
-
-	/* Ensure that only a single signal scope determining flag is set. */
-	if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1)
-		return -EINVAL;
+	switch (flags) {
+	case 0:
+		/* but see the PIDFD_THREAD check below */
+		type = PIDTYPE_TGID;
+		break;
+	case PIDFD_SIGNAL_THREAD:
+		type = PIDTYPE_PID;
+		break;
+	case PIDFD_SIGNAL_THREAD_GROUP:
+		type = PIDTYPE_TGID;
+		break;
+	case PIDFD_SIGNAL_PROCESS_GROUP:
+		type = PIDTYPE_PGID;
+		break;
+	}
 
 	f = fdget(pidfd);
 	if (!f.file)
@@ -3926,24 +3930,8 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
 	if (!access_pidfd_pidns(pid))
 		goto err;
 
-	switch (flags) {
-	case 0:
-		/* Infer scope from the type of pidfd. */
-		if (f.file->f_flags & PIDFD_THREAD)
-			type = PIDTYPE_PID;
-		else
-			type = PIDTYPE_TGID;
-		break;
-	case PIDFD_SIGNAL_THREAD:
+	if (!flags && (f.file->f_flags & PIDFD_THREAD))
 		type = PIDTYPE_PID;
-		break;
-	case PIDFD_SIGNAL_THREAD_GROUP:
-		type = PIDTYPE_TGID;
-		break;
-	case PIDFD_SIGNAL_PROCESS_GROUP:
-		type = PIDTYPE_PGID;
-		break;
-	}
 
 	if (info) {
 		ret = copy_siginfo_from_user_any(&kinfo, info);