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 <[email protected]>
Thanks!
[0] https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Wang Jinchao <[email protected]>
> ---
> V2:
> To satisfy Sparse, use rcu_dereference_protected.
> Reported-by: kernel test robot <[email protected]>
> Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
>
> 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
>