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

[Shivam Kumar]

On Fri, Aug 14, 2026 at 3:48 PM Shivam Kumar
<kumar.shivam43666 at gmail.com> 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.
>
> Fixes: 872d26a391da ("nvmet-tcp: add NVMe over TCP target driver")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Shivam Kumar <kumar.shivam43666 at gmail.com>
> Cc: stable at vger.kernel.org
> ---
>  drivers/nvme/target/tcp.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
> index 75a276d73be3..c9c98b8eb149 100644
> --- a/drivers/nvme/target/tcp.c
> +++ b/drivers/nvme/target/tcp.c
> @@ -1229,6 +1229,8 @@ static int nvmet_tcp_try_recv_pdu(struct nvmet_tcp_queue *queue)
>                 }
>
>                 queue->left = hdr->hlen - queue->offset + hdgst;
> +               if (queue->left > sizeof(queue->pdu) - queue->offset)
> +                       return -EPROTO;
>                 goto recv;
>         }
>
> --
> 2.53.0
>
Gentle ping on this one.