In the Linux kernel, the following vulnerability has been resolved: nfc: st21nfca: validate ATR_REQ length against the received frame st21

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

nfc: st21nfca: validate ATR_REQ length against the received frame

st21nfca_tm_recv_atr_req() checks that the received ATR_REQ frame is at
least ST21NFCA_ATR_REQ_MIN_SIZE and that the self-declared atr_req->length
is at least sizeof(struct st21nfca_atr_req), but never checks that
atr_req->length does not exceed the actual received length (skb->len).

st21nfca_tm_send_atr_res() then trusts the declared length:

 1gb_len = atr_req->length - sizeof(struct st21nfca_atr_req);
 2...
 3memcpy(atr_res->gbi, atr_req->gbi, gb_len);

so an RF peer that sends a short frame but sets atr_req->length larger
than the frame makes gb_len exceed the general bytes actually present,
and the memcpy reads out of bounds past the received skb. Those bytes are
placed in the ATR_RES and sent back to the peer (kernel-memory disclosure
to a proximity attacker); a larger declared length is an out-of-bounds
read (DoS).

Reject frames whose declared length exceeds the received length. The
adjacent nfc_tm_activated() path in the same function already derives its
general-bytes length from skb->len rather than the declared field.

Found by 0sec (https://0sec.ai) using automated source analysis; the
missing bound is evident from source. Compile-tested.