syscall: fix closing of reordered FDs in plan9 ForkExec

After dup'ing file descriptors in syscall.ProcAttr.Files to pass
to the exec'ed process, the logic for closing the old descriptors
was incorrect and could close the new descriptor instead.

Fixes #57180

Change-Id: I7725f21a465ffba57050fe4e36f3d36ba181cfb2
Reviewed-on: https://go-review.googlesource.com/c/go/+/457115
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: David du Colombier <0intro@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

diff --git a/src/syscall/exec_plan9.go b/src/syscall/exec_plan9.go
index d6b7890f55137f44c019a28743d72ecfa6c1e362..8f28b5aa22adbefc2d7f18f356e7323e4c9aa51a 100644 (file)
--- a/src/syscall/exec_plan9.go
+++ b/src/syscall/exec_plan9.go
@@ -276,7 +276,7 @@ dirloop:
 
        // Pass 3: close fd[i] if it was moved in the previous pass.
        for i = 0; i < len(fd); i++ {
-               if fd[i] >= 0 && fd[i] != int(i) {
+               if fd[i] >= len(fd) {
                        RawSyscall(SYS_CLOSE, uintptr(fd[i]), 0, 0)
                }
        }