From: Nick Alcock <nick.alcock@oracle.com>
Date: Thu, 10 Oct 2013 23:32:25 +0000 (+0100)
Subject: dtrace: armour ustack() against kernel threads, !task->mm, and corrupt usersp.
X-Git-Tag: v4.1.12-111.0.20170907_2225~3^2~3^2~119
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=1e6c9a5bcbfde68912704174860aecf32c902a40;p=users%2Fjedix%2Flinux-maple.git

dtrace: armour ustack() against kernel threads, !task->mm, and corrupt usersp.

Kernel threads have no userspace stack, by definition: we should not assume they
do.  Further, tasks with no mm (whether because they are kernel threads or for
any other reason) should not be ustack()ed, nor tasks in which find_vma() cannot
find the vma corresponding to the usersp.  (Possible causes for this might be a
task which just smashed its own userspace sp or a task which is in the middle of
exiting or exec()ing.)

Orabug: 17591351

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
---

diff --git a/dtrace/dtrace_isa.c b/dtrace/dtrace_isa.c
index 189d170581697..732d652e8539e 100644
--- a/dtrace/dtrace_isa.c
+++ b/dtrace/dtrace_isa.c
@@ -284,8 +284,17 @@ void dtrace_getufpstack(uint64_t *pcstack, uint64_t *fpstack,
 {
 	struct task_struct	*p = current;
 	unsigned long		*sp = (unsigned long *)this_cpu_read(old_rsp);
-	unsigned long		*bos = (unsigned long *)p->mm->start_stack;
-	struct vm_area_struct   *stack_vma = find_vma(p->mm, p->thread.usersp);
+	unsigned long		*bos;
+	struct vm_area_struct   *stack_vma;
+
+	if ((p->mm == NULL) || (p->flags & PF_KTHREAD))
+	    return;
+
+	bos = (unsigned long *)p->mm->start_stack;
+	stack_vma = find_vma(p->mm, p->thread.usersp);
+
+	if (stack_vma == NULL)
+	    return;
 
 	*pcstack++ = (uint64_t)p->pid;
 	pcstack_limit--;