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, 30 insertions, 3 deletions

diff --git a/src/syscall/syscall_linux_arm.go b/src/syscall/syscall_linux_arm.go
index f4740af586..600ec3552d 100644
--- a/src/syscall/syscall_linux_arm.go
+++ b/src/syscall/syscall_linux_arm.go
@@ -159,9 +159,9 @@ func Getrlimit(resource int, rlim *Rlimit) (err error) {
 	return
 }
 
-//sysnb setrlimit(resource int, rlim *rlimit32) (err error) = SYS_SETRLIMIT
+//sysnb setrlimit1(resource int, rlim *rlimit32) (err error) = SYS_SETRLIMIT
 
-func Setrlimit(resource int, rlim *Rlimit) (err error) {
+func setrlimit(resource int, rlim *Rlimit) (err error) {
 	err = prlimit(0, resource, rlim, nil)
 	if err != ENOSYS {
 		return err
@@ -183,7 +183,34 @@ func Setrlimit(resource int, rlim *Rlimit) (err error) {
 		return EINVAL
 	}
 
-	return setrlimit(resource, &rl)
+	return setrlimit1(resource, &rl)
+}
+
+//go:nosplit
+func rawSetrlimit(resource int, rlim *Rlimit) Errno {
+	_, _, errno := RawSyscall6(SYS_PRLIMIT64, 0, uintptr(resource), uintptr(unsafe.Pointer(rlim)), 0, 0, 0)
+	if errno != ENOSYS {
+		return errno
+	}
+
+	rl := rlimit32{}
+	if rlim.Cur == rlimInf64 {
+		rl.Cur = rlimInf32
+	} else if rlim.Cur < uint64(rlimInf32) {
+		rl.Cur = uint32(rlim.Cur)
+	} else {
+		return EINVAL
+	}
+	if rlim.Max == rlimInf64 {
+		rl.Max = rlimInf32
+	} else if rlim.Max < uint64(rlimInf32) {
+		rl.Max = uint32(rlim.Max)
+	} else {
+		return EINVAL
+	}
+
+	_, _, errno = RawSyscall(SYS_SETRLIMIT, uintptr(resource), uintptr(unsafe.Pointer(rlim)), 0)
+	return errno
 }
 
 func (r *PtraceRegs) PC() uint64 { return uint64(r.Uregs[15]) }