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syscall: use clone3 syscall with CLONE_NEWTIME

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CLONE_NEWTIME can only be used with the clone3 and unshare system calls,
see 769071ac9f:

> All available clone flags have been used, so CLONE_NEWTIME uses the highest
> bit of CSIGNAL. It means that it can be used only with the unshare() and
> the clone3() system calls.

The clone3 syscall was added in Linux kernel version 5.3 and
CLONE_NEWTIME was added in version 5.6. However, it was non-functional
until version 6.3 (and stable versions with the corresponding fix [1]).

[1] https://lore.kernel.org/lkml/20230308105126.10107-1-tklauser@distanz.ch/

In case CLONE_NEWTIME is set in SysProcAttr.Cloneflags on an unsupported
kernel version, the fork/exec call will fail.

Fixes #49779

Change-Id: Ic3ecfc2b601bafaab12b1805d7f9512955a8c7e2
Reviewed-on: https://go-review.googlesource.com/c/go/+/474356
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Tobias Klauser 2023-03-08 12:49:10 +01:00 committed by Gopher Robot
parent 778627f331
commit 7c019c62fb
2 changed files with 51 additions and 0 deletions
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5
src/syscall/exec_linux.go
View File

@ -293,6 +293,11 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
exitSignal: uint64(SIGCHLD),
cgroup: uint64(sys.CgroupFD),
}
} else if flags&CLONE_NEWTIME != 0 {
clone3 = &cloneArgs{
flags: uint64(flags),
exitSignal: uint64(SIGCHLD),
}
}
// About to call fork.

46
src/syscall/exec_linux_test.go
View File

@ -487,6 +487,52 @@ func TestUseCgroupFDHelper(*testing.T) {
fmt.Print(string(selfCg))
}
func TestCloneTimeNamespace(t *testing.T) {
testenv.MustHaveExec(t)
if os.Getenv("GO_WANT_HELPER_PROCESS") == "1" {
timens, err := os.Readlink("/proc/self/ns/time")
if err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(2)
}
fmt.Print(string(timens))
os.Exit(0)
}
exe, err := os.Executable()
if err != nil {
t.Fatal(err)
}
cmd := testenv.Command(t, exe, "-test.run=TestCloneTimeNamespace")
cmd.Env = append(cmd.Environ(), "GO_WANT_HELPER_PROCESS=1")
cmd.SysProcAttr = &syscall.SysProcAttr{
Cloneflags: syscall.CLONE_NEWTIME,
}
out, err := cmd.CombinedOutput()
if err != nil {
if isNotSupported(err) {
// CLONE_NEWTIME does not appear to be supported.
t.Skipf("skipping, CLONE_NEWTIME not supported: %v", err)
}
t.Fatalf("Cmd failed with err %v, output: %s", err, out)
}
// Inode numer of the time namespaces should be different.
// Based on https://man7.org/linux/man-pages/man7/time_namespaces.7.html#EXAMPLES
timens, err := os.Readlink("/proc/self/ns/time")
if err != nil {
t.Fatal(err)
}
parentTimeNS := string(timens)
childTimeNS := string(out)
if childTimeNS == parentTimeNS {
t.Fatalf("expected child time namespace to be different from parent time namespace: %s", parentTimeNS)
}
}
type capHeader struct {
version uint32
pid int32