In the Linux kernel, the following vulnerability has been resolved:  padata: Fix refcnt handling in padatafreeshell()  In a high-load arm64 environment, the pcryptaead01 test in LTP can lead to system UAF (Use-After-Free) issues. Due to the lengthy analysis of the pcryptaead01 function call, I'll describe the problem scenario using a simplified model:  Suppose there's a user of padata named user_function that adheres to the padata requirement of calling padata_free_shell after serial() has been invoked, as demonstrated in the following code:  c struct request {     struct padata_priv padata;     struct completion *done; };  void parallel(struct padata_priv *padata) {     do_something(); }  void serial(struct padata_priv *padata) {     struct request *request = container_of(padata,                    struct request,                 padata);     complete(request->done); }  void user_function() {     DECLARE_COMPLETION(done)     padata->parallel = parallel;     padata->serial = serial;     padata_do_parallel();     wait_for_completion(&done);     padata_free_shell(); }  In the corresponding padata.c file, there's the following code:  c static void padata_serial_worker(struct work_struct *serial_work) {     ...     cnt = 0;      while (!list_empty(&local_list)) {         ...         padata->serial(padata);         cnt++;     }      local_bh_enable();      if (refcount_sub_and_test(cnt, &pd->refcnt))         padata_free_pd(pd); }  Because of the high system load and the accumulation of unexecuted softirq at this moment, local_bh_enable() in padata takes longer to execute than usual. Subsequently, when accessing pd->refcnt, pd has already been released by padata_free_shell(), resulting in a UAF issue with pd->refcnt.  The fix is straightforward: add refcount_dec_and_test before calling padata_free_pd in padata_free_shell.