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

net: stmmac: fix TSO header length truncation

stmmac tso xmit() stores the protocol header length returned by stmmac tso header size() in a u8. stmmac tso valid packet() admits headers up to 1023 bytes, so a header longer than 255 bytes wraps modulo 256 (486 becomes 230, 256 becomes 0).

A TCP over IPv6 socket carrying a few hundred bytes of sticky destination/hop-by-hop options makes skb tcp all headers() exceed 255 while staying below the 1023-byte limit, so such an skb reaches stmmac tso xmit().

Widen proto hdr len to unsigned int, which is sufficient since the value is bounded by the hardware limit, and adjust the debug print specifier accordingly.