register_lock_class() can return NULL when the lock class pool is
exhausted, graph_lock() fails, or key validation fails. However,
__lock_set_class() uses the return value directly in pointer arithmetic
without a NULL check:
class = register_lock_class(lock, subclass, 0);
hlock->class_idx = class - lock_classes;
If class is NULL, this computes a wild offset that corrupts
hlock->class_idx. The subsequent reacquire_held_locks() call will
invoke hlock_class() with this corrupted index, leading to a NULL or
out-of-bounds pointer dereference.
Add the missing NULL check, consistent with how __lock_acquire() already
handles this case at the same call site.
Fixes: 64aa348edc ("lockdep: lock_set_subclass - reset a held lock's subclass")
Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>
Link: https://patch.msgid.link/h2kfw43n4527x6mgi2lwpz2rieqnfzgictpv4wr5nyfjkc47co@2r5vz4uz44db
7577e00b9a