x86/fpu: Do not leak fpstate pointer on fork

If fork fails early then the copied task struct would carry the fpstate
pointer of the parent task.

Not a problem right now, but later when dynamically allocated buffers
are available, keeping the pointer might result in freeing the
parent's buffer. Set it to NULL which prevents that. If fork reaches
clone_thread(), the pointer will be correctly set to the new task
context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.817101108@linutronix.de

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 5cd8208..c74c7e8 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -87,6 +87,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_VM86
        dst->thread.vm86 = NULL;
 #endif
+       /* Drop the copied pointer to current's fpstate */
+       dst->thread.fpu.fpstate = NULL;
        return 0;
 }