kprobes: bugfix: try_module_get even if calling_mod is NULL

When someone called register_*probe() from kernel-core code(not from
module) and that probes a kernel module, users can remove the probed
module because kprobe doesn't increment reference counter of the module.
(on the other hand, if the kernel-module calls register_*probe, kprobe
increments refcount of the probed module.)

Currently, we have no register_*probe() calling from kernel-core(except
smoke-test, but the smoke-test doesn't probe module), so there is no real
bugs.  But the logic is wrong(or not fair) and it can causes a problem
when someone might want to probe module from kernel.

After this patch is applied, even if someone put register_*probe() call in
the kernel-core code, it increments the reference counter of the probed
module, and it prevents user to remove the module until stopping probing
it.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.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>

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9f8a3f25259a9da4c8535bab07014b07da79a643..3afd354c46f1ebac4e6a86cf5912c763a03725d3 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -634,7 +634,7 @@ static int __kprobes __register_kprobe(struct kprobe *p,
                 * avoid incrementing the module refcount, so as to allow
                 * unloading of self probing modules.
                 */
-               if (calling_mod && calling_mod != probed_mod) {
+               if (calling_mod != probed_mod) {
                        if (unlikely(!try_module_get(probed_mod))) {
                                preempt_enable();
                                return -EINVAL;