[release-branch.go1.16] syscall: 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.

Updates #50057

Change-Id: Ie8955025dbd20702fabadc9bbe1d1a5ac0f36305
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1291271
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/370515
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>

17 files changed, 105 insertions, 51 deletions

diff --git a/src/syscall/syscall_aix.go b/src/syscall/syscall_aix.go
index 9c6afba442..db289fd39c 100644
--- a/src/syscall/syscall_aix.go
+++ b/src/syscall/syscall_aix.go
@@ -64,8 +64,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe(&pp)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_darwin.go b/src/syscall/syscall_darwin.go
index afdadbf894..2d4aa5867e 100644
--- a/src/syscall/syscall_darwin.go
+++ b/src/syscall/syscall_darwin.go
@@ -93,8 +93,10 @@ func Pipe(p []int) (err error) {
 	}
 	var q [2]int32
 	err = pipe(&q)
-	p[0] = int(q[0])
-	p[1] = int(q[1])
+	if err == nil {
+		p[0] = int(q[0])
+		p[1] = int(q[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_dragonfly.go b/src/syscall/syscall_dragonfly.go
index 0988fe4608..b3be59d02d 100644
--- a/src/syscall/syscall_dragonfly.go
+++ b/src/syscall/syscall_dragonfly.go
@@ -96,8 +96,11 @@ func Pipe(p []int) (err error) {
 	if len(p) != 2 {
 		return EINVAL
 	}
-	p[0], p[1], err = pipe()
-	return
+	r, w, err := pipe()
+	if err == nil {
+		p[0], p[1] = r, w
+	}
+	return err
 }
 
 //sys	extpread(fd int, p []byte, flags int, offset int64) (n int, err error)
diff --git a/src/syscall/syscall_freebsd.go b/src/syscall/syscall_freebsd.go
index 7c7b89aab9..ad904d6981 100644
--- a/src/syscall/syscall_freebsd.go
+++ b/src/syscall/syscall_freebsd.go
@@ -105,8 +105,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 
diff --git a/src/syscall/syscall_linux_386.go b/src/syscall/syscall_linux_386.go
index ed52647403..f08007b278 100644
--- a/src/syscall/syscall_linux_386.go
+++ b/src/syscall/syscall_linux_386.go
@@ -30,8 +30,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe(&pp)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -43,8 +45,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_amd64.go b/src/syscall/syscall_linux_amd64.go
index 5df3f796d1..896117adc8 100644
--- a/src/syscall/syscall_linux_amd64.go
+++ b/src/syscall/syscall_linux_amd64.go
@@ -118,8 +118,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe(&pp)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -131,8 +133,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_arm.go b/src/syscall/syscall_linux_arm.go
index 4a3729f898..8f21f17d6f 100644
--- a/src/syscall/syscall_linux_arm.go
+++ b/src/syscall/syscall_linux_arm.go
@@ -34,8 +34,10 @@ func Pipe(p []int) (err error) {
 	if err == ENOSYS {
 		err = pipe(&pp)
 	}
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -47,8 +49,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_arm64.go b/src/syscall/syscall_linux_arm64.go
index f575c84c93..bfa7be96aa 100644
--- a/src/syscall/syscall_linux_arm64.go
+++ b/src/syscall/syscall_linux_arm64.go
@@ -152,8 +152,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, 0)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -165,8 +167,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_mips64x.go b/src/syscall/syscall_linux_mips64x.go
index ab25b7be6f..bb69b1dffb 100644
--- a/src/syscall/syscall_linux_mips64x.go
+++ b/src/syscall/syscall_linux_mips64x.go
@@ -108,8 +108,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, 0)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -121,8 +123,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_mipsx.go b/src/syscall/syscall_linux_mipsx.go
index 377946fc92..99a3fad401 100644
--- a/src/syscall/syscall_linux_mipsx.go
+++ b/src/syscall/syscall_linux_mipsx.go
@@ -119,8 +119,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -130,8 +132,11 @@ func Pipe(p []int) (err error) {
 	if len(p) != 2 {
 		return EINVAL
 	}
-	p[0], p[1], err = pipe()
-	return
+	r, w, err := pipe()
+	if err == nil {
+		p[0], p[1] = r, w
+	}
+	return err
 }
 
 //sys	mmap2(addr uintptr, length uintptr, prot int, flags int, fd int, pageOffset uintptr) (xaddr uintptr, err error)
diff --git a/src/syscall/syscall_linux_ppc64x.go b/src/syscall/syscall_linux_ppc64x.go
index 45bf667407..639d5c64ab 100644
--- a/src/syscall/syscall_linux_ppc64x.go
+++ b/src/syscall/syscall_linux_ppc64x.go
@@ -87,8 +87,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, 0)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -100,8 +102,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_riscv64.go b/src/syscall/syscall_linux_riscv64.go
index 2a0fe64d25..dd48f7c8db 100644
--- a/src/syscall/syscall_linux_riscv64.go
+++ b/src/syscall/syscall_linux_riscv64.go
@@ -155,8 +155,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, 0)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -168,8 +170,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_linux_s390x.go b/src/syscall/syscall_linux_s390x.go
index 0f6f6277bb..08e66136b8 100644
--- a/src/syscall/syscall_linux_s390x.go
+++ b/src/syscall/syscall_linux_s390x.go
@@ -80,8 +80,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, 0)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
@@ -93,8 +95,10 @@ func Pipe2(p []int, flags int) (err error) {
 	}
 	var pp [2]_C_int
 	err = pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_netbsd.go b/src/syscall/syscall_netbsd.go
index fc13b706b5..0754bad5ac 100644
--- a/src/syscall/syscall_netbsd.go
+++ b/src/syscall/syscall_netbsd.go
@@ -112,8 +112,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 
diff --git a/src/syscall/syscall_openbsd.go b/src/syscall/syscall_openbsd.go
index 5a5ba5a51b..18eafe3521 100644
--- a/src/syscall/syscall_openbsd.go
+++ b/src/syscall/syscall_openbsd.go
@@ -72,8 +72,10 @@ func Pipe2(p []int, flags int) error {
 	}
 	var pp [2]_C_int
 	err := pipe2(&pp, flags)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return err
 }
 
diff --git a/src/syscall/syscall_plan9.go b/src/syscall/syscall_plan9.go
index d16cad45d8..6a8ab97dc6 100644
--- a/src/syscall/syscall_plan9.go
+++ b/src/syscall/syscall_plan9.go
@@ -198,8 +198,10 @@ func Pipe(p []int) (err error) {
 	}
 	var pp [2]int32
 	err = pipe(&pp)
-	p[0] = int(pp[0])
-	p[1] = int(pp[1])
+	if err == nil {
+		p[0] = int(pp[0])
+		p[1] = int(pp[1])
+	}
 	return
 }
 
diff --git a/src/syscall/syscall_solaris.go b/src/syscall/syscall_solaris.go
index daa4b88a71..7640aac25b 100644
--- a/src/syscall/syscall_solaris.go
+++ b/src/syscall/syscall_solaris.go
@@ -55,7 +55,9 @@ func Pipe(p []int) (err error) {
 	if e1 != 0 {
 		err = Errno(e1)
 	}
-	p[0], p[1] = int(r0), int(w0)
+	if err == nil {
+		p[0], p[1] = int(r0), int(w0)
+	}
 	return
 }