Re: [PATCH net v2] mac802154: llsec: add skb_cow_data() before in-place crypto

[Simon Horman <horms@kernel.org>]

On Tue, May 26, 2026 at 08:37:26PM +0200, Doruk Tan Ozturk wrote:
> llsec_do_encrypt_unauth(), llsec_do_encrypt_auth(),
> llsec_do_decrypt_unauth(), and llsec_do_decrypt_auth() all perform
> in-place cryptographic transformations on skb data.  They build a
> scatterlist with sg_init_one() pointing into the skb's linear data area
> and then pass the same scatterlist as both src and dst to the crypto API
> (e.g. crypto_skcipher_encrypt/decrypt, crypto_aead_encrypt/decrypt).
> 
> On the RX path, __ieee802154_rx_handle_packet() clones the received skb
> before handing it to each subscriber via ieee802154_subif_frame().  The
> cloned skb shares the same underlying data buffer via reference
> counting.  When llsec_do_decrypt() subsequently modifies this shared
> buffer in place, it corrupts data that other clones -- potentially
> belonging to other sockets or subsystems -- still reference.
> 
> On the TX path, similar data sharing can occur when an skb's head has
> been cloned (skb_cloned() returns true).
> 
> The fix is to call skb_cow_data() before performing any in-place crypto
> operation.  skb_cow_data() ensures that the skb's data area is not
> shared: if the skb head is cloned or the data spans multiple fragments,
> it copies the data into a private buffer that can be safely modified in
> place.  This is the same pattern used by:
> 
>   - ESP (net/ipv4/esp4.c, net/ipv6/esp6.c)
>   - MACsec (drivers/net/macsec.c)
>   - WireGuard (drivers/net/wireguard/receive.c)
>   - TIPC (net/tipc/crypto.c)
> 
> Without this guard, in-place crypto on shared skb data leads to:
>   - Silent data corruption of other skb clones
>   - Use-after-free when the crypto API scatterwalk writes through a
>     page that has already been freed by another clone's kfree_skb()
>   - Kernel crashes under concurrent 802.15.4 traffic with security
>     enabled (KASAN/KMSAN reports slab-use-after-free)
> 
> Found by 0sec (https://0sec.ai) using automated source analysis.
> 
> Fixes: 4c14a2fb5d14 ("mac802154: add llsec decryption method")
> Fixes: 03556e4d0dbb ("mac802154: add llsec encryption method")
> Cc: stable@vger.kernel.org
> Reported-by: Doruk Tan Ozturk <doruk@0sec.ai>
> Closes: https://lore.kernel.org/linux-wpan/20260525161806.96158-1-doruk@0sec.ai/
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
> ---
> v2:
>   - mark as net fix per Olek's review
>   - add Closes tag
>   - add Reviewed-by

FTR: An AI generated review of this patch is available on sashiko.dev.
I believe that review can be treated in the context of possible follow-up
and should not effect the progress of this patch.