kprobes: disable preempt for module_text_address() and kernel_text_address()
Masami Hiramatsu [Wed, 12 Nov 2008 21:26:51 +0000 (13:26 -0800)]
__register_kprobe() can be preempted after checking probing address but
before module_text_address() or try_module_get(), and in this interval
the module can be unloaded.  In that case, try_module_get(probed_mod)
will access to invalid address, or kprobe will probe invalid address.

This patch uses preempt_disable() to protect it and uses
__module_text_address() and __kernel_text_address().

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kprobes.c

index 8b57a25..f83c5e4 100644 (file)
@@ -613,30 +613,37 @@ static int __kprobes __register_kprobe(struct kprobe *p,
                return -EINVAL;
        p->addr = addr;
 
-       if (!kernel_text_address((unsigned long) p->addr) ||
-           in_kprobes_functions((unsigned long) p->addr))
+       preempt_disable();
+       if (!__kernel_text_address((unsigned long) p->addr) ||
+           in_kprobes_functions((unsigned long) p->addr)) {
+               preempt_enable();
                return -EINVAL;
+       }
 
        p->mod_refcounted = 0;
 
        /*
         * Check if are we probing a module.
         */
-       probed_mod = module_text_address((unsigned long) p->addr);
+       probed_mod = __module_text_address((unsigned long) p->addr);
        if (probed_mod) {
-               struct module *calling_mod = module_text_address(called_from);
+               struct module *calling_mod;
+               calling_mod = __module_text_address(called_from);
                /*
                 * We must allow modules to probe themself and in this case
                 * avoid incrementing the module refcount, so as to allow
                 * unloading of self probing modules.
                 */
                if (calling_mod && calling_mod != probed_mod) {
-                       if (unlikely(!try_module_get(probed_mod)))
+                       if (unlikely(!try_module_get(probed_mod))) {
+                               preempt_enable();
                                return -EINVAL;
+                       }
                        p->mod_refcounted = 1;
                } else
                        probed_mod = NULL;
        }
+       preempt_enable();
 
        p->nmissed = 0;
        INIT_LIST_HEAD(&p->list);
@@ -718,6 +725,10 @@ static void __kprobes __unregister_kprobe_bottom(struct kprobe *p)
        struct kprobe *old_p;
 
        if (p->mod_refcounted) {
+               /*
+                * Since we've already incremented refcount,
+                * we don't need to disable preemption.
+                */
                mod = module_text_address((unsigned long)p->addr);
                if (mod)
                        module_put(mod);