mac802154: llsec: add skb_cow_data() before in-place crypto

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>
Closes: <link to your mail on lore>
Link: https://lore.kernel.org/20260526183726.56100-1-doruk@0sec.ai
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

diff --git a/net/mac802154/llsec.c b/net/mac802154/llsec.c
index e8512578398e5aba04d637c0319fd48c89cf3c7f..5e7cc11fab3a43356f227847160554e3ba14f4bc 100644 (file)
--- a/net/mac802154/llsec.c
+++ b/net/mac802154/llsec.c
@@ -710,6 +710,7 @@ int mac802154_llsec_encrypt(struct mac802154_llsec *sec, struct sk_buff *skb)
 {
        struct ieee802154_hdr hdr;
        int rc, authlen, hlen;
+       struct sk_buff *trailer;
        struct mac802154_llsec_key *key;
        u32 frame_ctr;
 
@@ -769,6 +770,12 @@ int mac802154_llsec_encrypt(struct mac802154_llsec *sec, struct sk_buff *skb)
        skb->mac_len = ieee802154_hdr_push(skb, &hdr);
        skb_reset_mac_header(skb);
 
+       rc = skb_cow_data(skb, 0, &trailer);
+       if (rc < 0) {
+               llsec_key_put(key);
+               return rc;
+       }
+
        rc = llsec_do_encrypt(skb, sec, &hdr, key);
        llsec_key_put(key);
 
@@ -908,6 +915,13 @@ llsec_do_decrypt(struct sk_buff *skb, const struct mac802154_llsec *sec,
                 const struct ieee802154_hdr *hdr,
                 struct mac802154_llsec_key *key, __le64 dev_addr)
 {
+       struct sk_buff *trailer;
+       int err;
+
+       err = skb_cow_data(skb, 0, &trailer);
+       if (err < 0)
+               return err;
+
        if (hdr->sec.level == IEEE802154_SCF_SECLEVEL_ENC)
                return llsec_do_decrypt_unauth(skb, sec, hdr, key, dev_addr);
        else