jump_label: Fix NULL dereference bug in __jump_label_mod_update()

Commit 19483677684b ("jump_label: Annotate entries that operate on
__init code earlier") refactored the code that manages runtime
patching of jump labels in modules that are tied to static keys
defined in other modules or in the core kernel.

In the latter case, we may iterate over the static_key_mod linked
list until we hit the entry for the core kernel, whose 'mod' field
will be NULL, and attempt to dereference it to get at its 'state'
member.

So let's add a non-NULL check: this forces the 'init' argument of
__jump_label_update() to false for static keys that are defined in
the core kernel, which is appropriate given that __init annotated
jump_label entries in the core kernel should no longer be active
at this point (i.e., when loading modules).

Fixes: 19483677684b ("jump_label: Annotate entries that operate on ...")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20181001081324.11553-1-ard.biesheuvel@linaro.org

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index e8cf3ff3149cd645a1445532056259215e76d0b2..14a7f98817458c3d440a7c46878feb3cadb66ad0 100644 (file)
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -516,7 +516,7 @@ static void __jump_label_mod_update(struct static_key *key)
                else
                        stop = m->jump_entries + m->num_jump_entries;
                __jump_label_update(key, mod->entries, stop,
-                                   m->state == MODULE_STATE_COMING);
+                                   m && m->state == MODULE_STATE_COMING);
        }
 }