linux-hardening - Re: Coverity: __do_sys_pidfd_send

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Date: Wed, 14 Feb 2024 10:06:41 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Tycho Andersen <tycho@...ho.pizza>
Cc: coverity-bot <keescook@...omium.org>,
	Christian Brauner <brauner@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Peng Zhang <zhangpeng.00@...edance.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mateusz Guzik <mjguzik@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Tycho Andersen <tandersen@...flix.com>,
	Mike Christie <michael.christie@...cle.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	linux-kernel@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavo@...eddedor.com>,
	linux-next@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: Coverity: __do_sys_pidfd_send_signal(): UNINIT

On 02/14, Oleg Nesterov wrote:
>
> 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.

forgot about -EINVAL ...

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 +3899,23 @@ 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)
+	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;
+	default:
 		return -EINVAL;
+	}
 
 	f = fdget(pidfd);
 	if (!f.file)
@@ -3926,24 +3932,8 @@ 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);