CVE-2026-63831

In the Linux kernel, the following vulnerability has been resolved:

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

llsecdoencryptunauth(), llsecdoencryptauth(), llsecdodecryptunauth(), and llsecdodecryptauth() all perform in-place cryptographic transformations on skb data. They build a scatterlist with sginitone() 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. cryptoskcipherencrypt/decrypt, cryptoaeadencrypt/decrypt).

On the RX path, _ieee802154rxhandlepacket() clones the received skb before handing it to each subscriber via ieee802154subifframe(). The cloned skb shares the same underlying data buffer via reference counting. When llsecdodecrypt() 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 skbcowdata() before performing any in-place crypto operation. skbcowdata() 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.