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

[Andrea Parri <parri.andrea@gmail.com>]

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.

Fixes: 0faa0fe6f90e ("nvmet: New NVMe PCI endpoint function target driver")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
For stable, this depends on patch 4/5: without it, the new Data SGL
Length Invalid error is still reported to the host as a success.

 drivers/nvme/target/pci-epf.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/target/pci-epf.c b/drivers/nvme/target/pci-epf.c
index 4c5fff232fb99..a8df176c1a574 100644
--- a/drivers/nvme/target/pci-epf.c
+++ b/drivers/nvme/target/pci-epf.c
@@ -1073,10 +1073,22 @@ static int nvmet_pci_epf_iod_parse_sgl_segments(struct nvmet_pci_epf_ctrl *ctrl,
 	return 0;
 }
 
+static u64 nvmet_pci_epf_iod_data_segs_len(struct nvmet_pci_epf_iod *iod)
+{
+	u64 len = 0;
+	int i;
+
+	for (i = 0; i < iod->nr_data_segs; i++)
+		len += iod->data_segs[i].length;
+
+	return len;
+}
+
 static int nvmet_pci_epf_iod_parse_sgls(struct nvmet_pci_epf_iod *iod)
 {
 	struct nvmet_pci_epf_ctrl *ctrl = iod->ctrl;
 	struct nvme_sgl_desc *sgl = &iod->cmd.common.dptr.sgl;
+	int ret;
 
 	if (sgl->type == (NVME_SGL_FMT_DATA_DESC << 4)) {
 		/* Single data descriptor case. */
@@ -1084,10 +1096,23 @@ static int nvmet_pci_epf_iod_parse_sgls(struct nvmet_pci_epf_iod *iod)
 		iod->data_segs = &iod->data_seg;
 		iod->data_seg.pci_addr = le64_to_cpu(sgl->addr);
 		iod->data_seg.length = le32_to_cpu(sgl->length);
-		return 0;
+	} else {
+		ret = nvmet_pci_epf_iod_parse_sgl_segments(ctrl, iod);
+		if (ret)
+			return ret;
 	}
 
-	return nvmet_pci_epf_iod_parse_sgl_segments(ctrl, iod);
+	/*
+	 * The command executes on data_len bytes, but each segment is
+	 * allocated and transferred in full, so they must describe exactly
+	 * data_len bytes.
+	 */
+	if (nvmet_pci_epf_iod_data_segs_len(iod) != iod->data_len) {
+		iod->status = NVME_SC_SGL_INVALID_DATA | NVME_STATUS_DNR;
+		return -EINVAL;
+	}
+
+	return 0;
 }
 
 static int nvmet_pci_epf_alloc_iod_data_buf(struct nvmet_pci_epf_iod *iod)
-- 
2.53.0