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, 12 insertions, 1 deletions

diff --git a/src/syscall/syscall_linux.go b/src/syscall/syscall_linux.go
index bf9d85637a..618b2e6d42 100644
--- a/src/syscall/syscall_linux.go
+++ b/src/syscall/syscall_linux.go
@@ -1058,7 +1058,7 @@ func Getpgrp() (pid int) {
 //sys	Mknodat(dirfd int, path string, mode uint32, dev int) (err error)
 //sys	Nanosleep(time *Timespec, leftover *Timespec) (err error)
 //sys	PivotRoot(newroot string, putold string) (err error) = SYS_PIVOT_ROOT
-//sysnb prlimit(pid int, resource int, newlimit *Rlimit, old *Rlimit) (err error) = SYS_PRLIMIT64
+//sysnb prlimit1(pid int, resource int, newlimit *Rlimit, old *Rlimit) (err error) = SYS_PRLIMIT64
 //sys	read(fd int, p []byte) (n int, err error)
 //sys	Removexattr(path string, attr string) (err error)
 //sys	Setdomainname(p []byte) (err error)
@@ -1261,3 +1261,14 @@ func Munmap(b []byte) (err error) {
 //sys	Munlock(b []byte) (err error)
 //sys	Mlockall(flags int) (err error)
 //sys	Munlockall() (err error)
+
+// prlimit changes a resource limit. We use a single definition so that
+// we can tell StartProcess to not restore the original NOFILE limit.
+// This is unexported but can be called from x/sys/unix.
+func prlimit(pid int, resource int, newlimit *Rlimit, old *Rlimit) (err error) {
+	err = prlimit1(pid, resource, newlimit, old)
+	if err == nil && newlimit != nil && resource == RLIMIT_NOFILE {
+		origRlimitNofile.Store(Rlimit{0, 0})
+	}
+	return err
+}