On Thu, Sep 28, 2023 at 08:38:53AM +0800, Wang Jinchao wrote: > In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead to > system UAF (Use-After-Free) issues. Due to the lengthy analysis of the > pcrypt_aead01 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`. This could use a Fixes tag. From Nicolai's patch[0] we agreed on Fixes: 07928d9bfc81 ("padata: Remove broken queue flushing") With that, Acked-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Thanks! [0] https://lore.kernel.org/all/87educb7rm.fsf@xxxxxxx/ > Signed-off-by: Wang Jinchao <wangjinchao@xxxxxxxxxxx> > --- > V2: > To satisfy Sparse, use rcu_dereference_protected. > Reported-by: kernel test robot <lkp@xxxxxxxxx> > Closes: https://lore.kernel.org/oe-kbuild-all/202309270829.xHgTOMKw-lkp@xxxxxxxxx/ > > V1: https://lore.kernel.org/all/ZRE4XvOOhz4HSOgR@fedora/ > > kernel/padata.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/padata.c b/kernel/padata.c > index 222d60195de6..acef1e703a8b 100644 > --- a/kernel/padata.c > +++ b/kernel/padata.c > @@ -1107,7 +1107,9 @@ void padata_free_shell(struct padata_shell *ps) > > mutex_lock(&ps->pinst->lock); > list_del(&ps->list); > - padata_free_pd(rcu_dereference_protected(ps->pd, 1)); > + struct parallel_data *pd = rcu_dereference_protected(ps->pd, 1); > + if (refcount_dec_and_test(&pd->refcnt)) > + padata_free_pd(pd); > mutex_unlock(&ps->pinst->lock); > > kfree(ps); > -- > 2.40.0 >