unix, plan9: avoid writing to p when Pipe(p) fails

Generally speaking Go functions make no guarantees
about what has happened to result parameters on error,
and Pipe is no exception: callers should avoid looking at
p if Pipe returns an error.

However, we had a bug in which ForkExec was using the
content of p after a failed Pipe, and others may too.
As a robustness fix, make Pipe avoid writing to p on failure.

windows.Pipe already avoided writing to p on failure.

For golang/go#50057.

Change-Id: I93ed06b06a9981793c119c1d7df689fbe79b4116
Reviewed-on: https://go-review.googlesource.com/c/sys/+/370614
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

plan9/syscall_plan9.go

@@ -132,8 +132,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]int32
 	err = pipe(&pp)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 

unix/syscall_aix.go

@@ -519,8 +519,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe(&pp)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 

unix/syscall_darwin.go

@@ -159,8 +159,10 @@ func Pipe(p []int) (err error) {
 	}
 	var x [2]int32
 	err = pipe(&x)
-	p[0] = int(x[0])
+	if err == nil {
-	p[1] = int(x[1])
+		p[0] = int(x[0])
+		p[1] = int(x[1])
+	}
 	return
 }
 

unix/syscall_dragonfly.go

@@ -101,7 +101,10 @@ func Pipe(p []int) (err error) {
 	if len(p) != 2 {
 		return EINVAL
 	}
-	p[0], p[1], err = pipe()
+	r, w, err := pipe()
+	if err == nil {
+		p[0], p[1] = r, w
+	}
 	return
 }
 
@@ -114,7 +117,10 @@ func Pipe2(p []int, flags int) (err error) {
 	var pp [2]_C_int
 	// pipe2 on dragonfly takes an fds array as an argument, but still
 	// returns the file descriptors.
-	p[0], p[1], err = pipe2(&pp, flags)
+	r, w, err := pipe2(&pp, flags)
+	if err == nil {
+		p[0], p[1] = r, w
+	}
 	return err
 }
 

unix/syscall_freebsd.go

@@ -110,8 +110,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 

unix/syscall_linux.go

@@ -131,8 +131,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 

unix/syscall_netbsd.go

@@ -128,8 +128,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 

unix/syscall_openbsd.go

@@ -87,8 +87,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 

unix/syscall_solaris.go

@@ -66,8 +66,10 @@ func Pipe(p []int) (err error) {
 	if n != 0 {
 		return err
 	}
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return nil
 }
 
@@ -79,8 +81,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 

unix/syscall_zos_s390x.go

@@ -579,8 +579,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe(&pp)
-	p[0] = int(pp[0])
+	if err == nil {
-	p[1] = int(pp[1])
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }