Re: [PATCH] nvmet-tcp: fix out-of-bounds write when receiving an over-long PDU

[Keith Busch <kbusch@kernel.org>]

On Fri, Aug 14, 2026 at 03:48:11PM -0400, Shivam Kumar wrote:
> nvmet_tcp_try_recv_pdu() reads a PDU header into the fixed 128-byte
> queue->pdu union, then computes the remaining payload length as
> 
> 	queue->left = hdr->hlen - queue->offset + hdgst;
> 
> and reads that many more bytes into &queue->pdu + queue->offset, without
> ever bounding the result against sizeof(queue->pdu).
> 
> A struct nvme_tcp_icreq_pdu is itself 128 bytes, exactly the size of the
> union. Once a header digest has been negotiated (hdgst = 4), a second
> ICReq passes the hlen == nvmet_tcp_pdu_size() check but yields
> queue->left = 128 - 8 + 4 = 124, so bytes 8..132 are written into the
> 128-byte buffer -- 4 bytes past its end, over queue->hdr_digest and
> queue->data_digest. Those bytes are attacker-controlled (an ICReq
> carries no digest), and the duplicate ICReq is only rejected later,
> after the overflow. A remote unauthenticated host can thus corrupt
> kernel memory adjacent to the receive buffer.
> 
> Reject any PDU whose declared length would read past the end of
> queue->pdu before the second recv.

Thanks, applied to nvme-7.3.