Re: [PATCH net] esp: Fix crash observed during device unregistration and decryption

[Steffen Klassert <steffen.klassert@secunet.com>]

On Wed, Mar 16, 2016 at 06:25:26PM -0600, Subash Abhinov Kasiviswanathan wrote:
> A crash is observed when a decrypted packet is processed in receive path.
> get_rps_cpus() tries to dereference the skb->dev fields but it appears
> that the device is freed from the poison pattern.
> 
> [<ffffffc000af58ec>] get_rps_cpu+0x94/0x2f0
> [<ffffffc000af5f94>] netif_rx_internal+0x140/0x1cc
> [<ffffffc000af6094>] netif_rx+0x74/0x94
> [<ffffffc000bc0b6c>] xfrm_input+0x754/0x7d0
> [<ffffffc000bc0bf8>] xfrm_input_resume+0x10/0x1c
> [<ffffffc000ba6eb8>] esp_input_done+0x20/0x30
> [<ffffffc0000b64c8>] process_one_work+0x244/0x3fc
> [<ffffffc0000b7324>] worker_thread+0x2f8/0x418
> [<ffffffc0000bb40c>] kthread+0xe0/0xec
> 
> -013|get_rps_cpu(
>      |    dev = 0xFFFFFFC08B688000,
>      |    skb = 0xFFFFFFC0C76AAC00 -> (
>      |      dev = 0xFFFFFFC08B688000 -> (
>      |        name =
> "......................................................
>      |        name_hlist = (next = 0xAAAAAAAAAAAAAAAA, pprev =
> 0xAAAAAAAAAAA
> 
> Following are the sequence of events observed -
> 
> - Encrypted packet in receive path from netdevice is queued
> - Encrypted packet queued for decryption (asynchronous)
> - Netdevice brought down and freed
> - Packet is decrypted and returned through callback in esp_input_done
> - Packet is queued again for process in network stack using netif_rx
> 
> Since the device appears to have been freed, the dereference of skb->dev in
> get_rps_cpus() leads to an unhandled page fault exception.
> 
> Fix this by holding on to device reference when queueing packets
> asynchronously and releasing the reference on call back return.
> 
> Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
> ---
>  net/ipv4/esp4.c | 2 ++
>  net/ipv6/esp6.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
> index 4779374..d482a96 100644
> --- a/net/ipv4/esp4.c
> +++ b/net/ipv4/esp4.c
> @@ -380,6 +380,7 @@ static void esp_input_done(struct crypto_async_request
> *base, int err)
>  {
>  	struct sk_buff *skb = base->data;
>  
> +	dev_put(skb->dev);

esp_input_done() is called just on asynchronous resumption, so you
leak the reference on synchronous crypto.

Also, other IPsec protocols need this too. So maybe better
to add this to xfrm_input().