Re: [PATCH 2/2] tracing: Add test for user space strings when filtering on string pointers

Hi Steve,

Steven Rostedt rostedt@goodmis.org writes:

From: Steven Rostedt rostedt@goodmis.org

Pingfan reported that the following causes a fault:

echo "filename ~ "cpu"" > events/syscalls/sys_enter_openat/filter echo 1 > events/syscalls/sys_enter_at/enable

[..]

+static __always_inline char *test_string(char *str) +{

• struct ustring_buffer *ubuf;
• char __user *ustr;
• char *kstr;
• if (!ustring_per_cpu)

• return NULL;
  

• ubuf = this_cpu_ptr(ustring_per_cpu);
• kstr = ubuf->buffer;
• if (likely((unsigned long)str >= TASK_SIZE)) {

I think that would not work on architectures where addresses for kernel and user space could overlap, i.e. with different address spaces?

• /* For safety, do not trust the string pointer */
  

• if (!strncpy_from_kernel_nofault(kstr, str, USTRING_BUF_SIZE))
  

• 	return NULL;
  

• } else {

• /* user space address? */
  

• ustr = str;
  

• if (!strncpy_from_user_nofault(kstr, ustr, USTRING_BUF_SIZE))
  

• 	return NULL;
  

• }
• return kstr;

+}