Re: [PATCH wpan] mac802154: fix llsec key resources release in mac802154_llsec_key_del

[Alexander Aring]

Hi,

On Wed, Feb 28, 2024 at 11:44 AM Fedor Pchelkin <pchelkin@xxxxxxxxx> wrote:
>
> mac802154_llsec_key_del() can free resources of a key directly without
> following the RCU rules for waiting before the end of a grace period. This
> may lead to use-after-free in case llsec_lookup_key() is traversing the
> list of keys in parallel with a key deletion:
>
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 4 PID: 16000 at lib/refcount.c:25 refcount_warn_saturate+0x162/0x2a0
> Modules linked in:
> CPU: 4 PID: 16000 Comm: wpan-ping Not tainted 6.7.0 #19
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> RIP: 0010:refcount_warn_saturate+0x162/0x2a0
> Call Trace:
>  <TASK>
>  llsec_lookup_key.isra.0+0x890/0x9e0
>  mac802154_llsec_encrypt+0x30c/0x9c0
>  ieee802154_subif_start_xmit+0x24/0x1e0
>  dev_hard_start_xmit+0x13e/0x690
>  sch_direct_xmit+0x2ae/0xbc0
>  __dev_queue_xmit+0x11dd/0x3c20
>  dgram_sendmsg+0x90b/0xd60
>  __sys_sendto+0x466/0x4c0
>  __x64_sys_sendto+0xe0/0x1c0
>  do_syscall_64+0x45/0xf0
>  entry_SYSCALL_64_after_hwframe+0x6e/0x76
>
> Also, ieee802154_llsec_key_entry structures are not freed by
> mac802154_llsec_key_del():
>
> unreferenced object 0xffff8880613b6980 (size 64):
>   comm "iwpan", pid 2176, jiffies 4294761134 (age 60.475s)
>   hex dump (first 32 bytes):
>     78 0d 8f 18 80 88 ff ff 22 01 00 00 00 00 ad de  x.......".......
>     00 00 00 00 00 00 00 00 03 00 cd ab 00 00 00 00  ................
>   backtrace:
>     [<ffffffff81dcfa62>] __kmem_cache_alloc_node+0x1e2/0x2d0
>     [<ffffffff81c43865>] kmalloc_trace+0x25/0xc0
>     [<ffffffff88968b09>] mac802154_llsec_key_add+0xac9/0xcf0
>     [<ffffffff8896e41a>] ieee802154_add_llsec_key+0x5a/0x80
>     [<ffffffff8892adc6>] nl802154_add_llsec_key+0x426/0x5b0
>     [<ffffffff86ff293e>] genl_family_rcv_msg_doit+0x1fe/0x2f0
>     [<ffffffff86ff46d1>] genl_rcv_msg+0x531/0x7d0
>     [<ffffffff86fee7a9>] netlink_rcv_skb+0x169/0x440
>     [<ffffffff86ff1d88>] genl_rcv+0x28/0x40
>     [<ffffffff86fec15c>] netlink_unicast+0x53c/0x820
>     [<ffffffff86fecd8b>] netlink_sendmsg+0x93b/0xe60
>     [<ffffffff86b91b35>] ____sys_sendmsg+0xac5/0xca0
>     [<ffffffff86b9c3dd>] ___sys_sendmsg+0x11d/0x1c0
>     [<ffffffff86b9c65a>] __sys_sendmsg+0xfa/0x1d0
>     [<ffffffff88eadbf5>] do_syscall_64+0x45/0xf0
>     [<ffffffff890000ea>] entry_SYSCALL_64_after_hwframe+0x6e/0x76
>
> Handle the proper resource release in the RCU callback function
> mac802154_llsec_key_del_rcu().
>
> Note that if llsec_lookup_key() finds a key, it gets a refcount via
> llsec_key_get() and locally copies key id from key_entry (which is a
> list element). So it's safe to call llsec_key_put() and free the list
> entry after the RCU grace period elapses.
>
> Found by Linux Verification Center (linuxtesting.org).
>
> Fixes: 5d637d5aabd8 ("mac802154: add llsec structures and mutators")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
> ---
> Should the patch be targeted to "net" tree directly?
>
>  include/net/cfg802154.h |  1 +
>  net/mac802154/llsec.c   | 18 +++++++++++++-----
>  2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/include/net/cfg802154.h b/include/net/cfg802154.h
> index cd95711b12b8..76d2cd2e2b30 100644
> --- a/include/net/cfg802154.h
> +++ b/include/net/cfg802154.h
> @@ -401,6 +401,7 @@ struct ieee802154_llsec_key {
>
>  struct ieee802154_llsec_key_entry {
>         struct list_head list;
> +       struct rcu_head rcu;
>
>         struct ieee802154_llsec_key_id id;
>         struct ieee802154_llsec_key *key;
> diff --git a/net/mac802154/llsec.c b/net/mac802154/llsec.c
> index 8d2eabc71bbe..f13b07ebfb98 100644
> --- a/net/mac802154/llsec.c
> +++ b/net/mac802154/llsec.c
> @@ -265,19 +265,27 @@ int mac802154_llsec_key_add(struct mac802154_llsec *sec,
>         return -ENOMEM;
>  }
>
> +static void mac802154_llsec_key_del_rcu(struct rcu_head *rcu)
> +{
> +       struct ieee802154_llsec_key_entry *pos;
> +       struct mac802154_llsec_key *mkey;
> +
> +       pos = container_of(rcu, struct ieee802154_llsec_key_entry, rcu);
> +       mkey = container_of(pos->key, struct mac802154_llsec_key, key);
> +
> +       llsec_key_put(mkey);
> +       kfree_sensitive(pos);

I don't think this kfree is right, "struct ieee802154_llsec_key_entry"
is declared as "non pointer" in "struct mac802154_llsec_key". The
memory that is part of "struct ieee802154_llsec_key_entry" should be
freed when llsec_key_put(), llsec_key_release() hits.

Or is there something I am missing here?

Thanks.

Otherwise the patch looks correct to me.

- Alex