Re: [PATCH 5/5] nvmet: pci-epf: require SGLs to match the command data length

[Christoph Hellwig <hch@lst.de>]

On Mon, Oct 12, 2026 at 04:12:32PM +0200, Andrea Parri wrote:
> The PCI endpoint target sends the host every byte a read command's SGL
> describes, even when the SGL describes more than the command transfers.
> The excess is kmalloc() memory the command never wrote, so the host
> receives stale target memory. Any successful read can do this,
> including Identify.
> 
> nvmet_pci_epf_alloc_iod_data_buf() allocates each segment at the length
> of its SGL data descriptor, but sets req->transfer_len from
> iod->data_len, the length the command implies. Once the command
> completes, nvmet_pci_epf_transfer_iod_data() sends every segment in
> full. Nothing compares the descriptor lengths with iod->data_len, and
> the MDTS check only bounds iod->data_len.
> 
> Fail the command with Data SGL Length Invalid when the data descriptors
> do not add up to iod->data_len, before any segment is allocated. The
> tcp and rdma transports take the data length from the SGL itself, so
> there most commands already reject a mismatch in
> nvmet_check_transfer_len(). PRP lists are built from iod->data_len and
> are unaffected.
> 
> Found by code inspection. Build-tested only (x86_64, W=1): no PCI
> endpoint hardware was available to run it.

Looks good, although again having this validated on hardware would
be really useful.