syscall: restore original NOFILE rlimit in child process

If we increased the NOFILE rlimit when starting the program,
restore the original rlimit when forking a child process.

For #46279

Change-Id: Ia5d2af9ef435e5932965c15eec2e428d2130d230
Reviewed-on: https://go-review.googlesource.com/c/go/+/476097
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Ian Lance Taylor <iant@google.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/syscall/exec_libc.go b/src/syscall/exec_libc.go
index 0f8a7b5375..44557867eb 100644
--- a/src/syscall/exec_libc.go
+++ b/src/syscall/exec_libc.go
@@ -53,6 +53,7 @@ func getpid() (pid uintptr, err Errno)
 func ioctl(fd uintptr, req uintptr, arg uintptr) (err Errno)
 func setgid(gid uintptr) (err Errno)
 func setgroups1(ngid uintptr, gid uintptr) (err Errno)
+func setrlimit1(which uintptr, lim unsafe.Pointer) (err Errno)
 func setsid() (pid uintptr, err Errno)
 func setuid(uid uintptr) (err Errno)
 func setpgid(pid uintptr, pgid uintptr) (err Errno)
@@ -90,6 +91,8 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		ngroups, groups uintptr
 	)
 
+	rlim, rlimOK := origRlimitNofile.Load().(Rlimit)
+
 	// guard against side effects of shuffling fds below.
 	// Make sure that nextfd is beyond any currently open files so
 	// that we can't run the risk of overwriting any of them.
@@ -292,6 +295,11 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		}
 	}
 
+	// Restore original rlimit.
+	if rlimOK && rlim.Cur != 0 {
+		setrlimit1(RLIMIT_NOFILE, unsafe.Pointer(&rlim))
+	}
+
 	// Time to exec.
 	err1 = execve(
 		uintptr(unsafe.Pointer(argv0)),