On 8/29/20 12:37 PM, Tuong Lien wrote:
> The 'this_cpu_ptr()' is used to obtain the AEAD key' TFM on the current
> CPU for encryption, however the execution can be preemptible since it's
> actually user-space context, so the 'using smp_processor_id() in
> preemptible' has been observed.
>
> We fix the issue by using the 'get/put_cpu_ptr()' API which consists of
> a 'preempt_disable()' instead.
>
> Fixes: fc1b6d6de220 ("tipc: introduce TIPC encryption & authentication")
Have you forgotten ' Reported-by:
syzbot+263f8c0d007dc09b2...@syzkaller.appspotmail.com' ?
> Acked-by: Jon Maloy <jma...@redhat.com>
> Signed-off-by: Tuong Lien <tuong.t.l...@dektech.com.au>
> ---
> net/tipc/crypto.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c
> index c38babaa4e57..7c523dc81575 100644
> --- a/net/tipc/crypto.c
> +++ b/net/tipc/crypto.c
> @@ -326,7 +326,8 @@ static void tipc_aead_free(struct rcu_head *rp)
> if (aead->cloned) {
> tipc_aead_put(aead->cloned);
> } else {
> - head = *this_cpu_ptr(aead->tfm_entry);
> + head = *get_cpu_ptr(aead->tfm_entry);
> + put_cpu_ptr(aead->tfm_entry);
Why is this safe ?
I think that this very unusual construct needs a comment, because this is not
obvious.
This really looks like an attempt to silence syzbot to me.
> list_for_each_entry_safe(tfm_entry, tmp, &head->list, list) {
> crypto_free_aead(tfm_entry->tfm);
> list_del(&tfm_entry->list);
> @@ -399,10 +400,15 @@ static void tipc_aead_users_set(struct tipc_aead __rcu
> *aead, int val)
> */
> static struct crypto_aead *tipc_aead_tfm_next(struct tipc_aead *aead)
> {
> - struct tipc_tfm **tfm_entry = this_cpu_ptr(aead->tfm_entry);
> + struct tipc_tfm **tfm_entry;
> + struct crypto_aead *tfm;
>
> + tfm_entry = get_cpu_ptr(aead->tfm_entry);
> *tfm_entry = list_next_entry(*tfm_entry, list);
> - return (*tfm_entry)->tfm;
> + tfm = (*tfm_entry)->tfm;
> + put_cpu_ptr(tfm_entry);
Again, this looks suspicious to me. I can not explain why this would be safe.
> +
> + return tfm;
> }
>
> /**
>
