[PATCH] kprobes: fix unloading of self probed module

When a kprobes modules is written in such a way that probes are inserted on
itself, then unload of that moudle was not possible due to reference
couning on the same module.

The below patch makes a check and incrementes the module refcount only if
it is not a self probed module.

We need to allow modules to probe themself for kprobes performance
measurements

This patch has been tested on several x86_64, ppc64 and IA64 architectures.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 35 insertions, 10 deletions

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 10005bc92a31..669756bc20a2 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -68,6 +68,9 @@ struct kprobe {
         /* list of kprobes for multi-handler support */
         struct list_head list;
 
+        /* Indicates that the corresponding module has been ref counted */
+        unsigned int mod_refcounted;
+
         /*count the number of times this probe was temporarily disarmed */
         unsigned long nmissed;
 
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 34a885bb82e0..3ea6325228da 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -449,19 +449,32 @@ static int __kprobes in_kprobes_functions(unsigned long addr)
         return 0;
 }
 
-int __kprobes register_kprobe(struct kprobe *p)
+static int __kprobes __register_kprobe(struct kprobe *p,
+        unsigned long called_from)
 {
         int ret = 0;
         struct kprobe *old_p;
-        struct module *mod;
+        struct module *probed_mod;
 
         if ((!kernel_text_address((unsigned long) p->addr)) ||
                 in_kprobes_functions((unsigned long) p->addr))
                 return -EINVAL;
 
-        if ((mod = module_text_address((unsigned long) p->addr)) &&
-                        (unlikely(!try_module_get(mod))))
-                return -EINVAL;
+        p->mod_refcounted = 0;
+        /* Check are we probing a module */
+        if ((probed_mod = module_text_address((unsigned long) p->addr))) {
+                struct module *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)))
+                                return -EINVAL;
+                        p->mod_refcounted = 1;
+                } else
+                        probed_mod = NULL;
+        }
 
         p->nmissed = 0;
         down(&kprobe_mutex);
@@ -483,11 +496,17 @@ int __kprobes register_kprobe(struct kprobe *p)
 out:
         up(&kprobe_mutex);
 
-        if (ret && mod)
-                module_put(mod);
+        if (ret && probed_mod)
+                module_put(probed_mod);
         return ret;
 }
 
+int __kprobes register_kprobe(struct kprobe *p)
+{
+        return __register_kprobe(p,
+                (unsigned long)__builtin_return_address(0));
+}
+
 void __kprobes unregister_kprobe(struct kprobe *p)
 {
         struct module *mod;
@@ -524,7 +543,8 @@ valid_p:
         up(&kprobe_mutex);
 
         synchronize_sched();
-        if ((mod = module_text_address((unsigned long)p->addr)))
+        if (p->mod_refcounted &&
+            (mod = module_text_address((unsigned long)p->addr)))
                 module_put(mod);
 
         if (cleanup_p) {
@@ -547,7 +567,8 @@ int __kprobes register_jprobe(struct jprobe *jp)
         jp->kp.pre_handler = setjmp_pre_handler;
         jp->kp.break_handler = longjmp_break_handler;
 
-        return register_kprobe(&jp->kp);
+        return __register_kprobe(&jp->kp,
+                (unsigned long)__builtin_return_address(0));
 }
 
 void __kprobes unregister_jprobe(struct jprobe *jp)
@@ -587,7 +608,8 @@ int __kprobes register_kretprobe(struct kretprobe *rp)
 
         rp->nmissed = 0;
         /* Establish function entry probe point */
-        if ((ret = register_kprobe(&rp->kp)) != 0)
+        if ((ret = __register_kprobe(&rp->kp,
+                (unsigned long)__builtin_return_address(0))) != 0)
                 free_rp_inst(rp);
         return ret;
 }