On Wed, Oct 04, 2023 at 10:54:29AM -0400, Daniel Jordan wrote: > 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); Oh, I should've also said please move the declaration of pd to the top of the function like scripts/checkpatch.pl suggests. > > + if (refcount_dec_and_test(&pd->refcnt)) > > + padata_free_pd(pd); > > mutex_unlock(&ps->pinst->lock); > > > > kfree(ps); > > -- > > 2.40.0 > >