[PATCH v3 4/4] um: Prohibit the VM_CLONE flag in run_helper_thread()

["Tiwei Bie" <tiwei.btw@antgroup.com>]

Directly creating helper threads with VM_CLONE using clone can
compromise the thread safety of errno. Since all these helper
threads have been converted to use os_run_helper_thread(), let's
prevent using this flag in run_helper_thread().

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
---
 arch/um/os-Linux/helper.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index df22cba24d82..89c2ad2a4e3a 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -122,6 +122,10 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
 	unsigned long stack, sp;
 	int pid, status, err;
 
+	/* To share memory space, use os_run_helper_thread() instead. */
+	if (flags & CLONE_VM)
+		return -EINVAL;
+
 	stack = alloc_stack(0, __uml_cant_sleep());
 	if (stack == 0)
 		return -ENOMEM;
-- 
2.34.1