[PATCH v2] nvme: nvme_identify_ns_descs: prevent oob

[Eugene Korenevsky <ekorenevsky@aliyun.com>]

Broken or malicious controller can send invalid ns id.
Out-of-band memory access may occur if remaining buffer size
is less than .nidl (ns id length) field of `struct nvme_ns_id_desc`

Fix this issue by counting remaining buffer length and checking
.nidl against it.

Signed-off-by: Eugene Korenevsky <ekorenevsky@aliyun.com>
---
v1->v2:
 * Simplification: do not touch nvme_process_ns_desc()
 * Update commit description
---
 drivers/nvme/host/core.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f1f719351f3f..62143f256a63 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1538,7 +1538,8 @@ static int nvme_identify_ns_descs(struct nvme_ctrl *ctrl,
 {
 	struct nvme_command c = { };
 	bool csi_seen = false;
-	int status, pos, len;
+	int status, len, remain;
+	struct nvme_ns_id_desc *cur;
 	void *data;
 
 	if (ctrl->vs < NVME_VS(1, 3, 0) && !nvme_multi_css(ctrl))
@@ -1563,17 +1564,21 @@ static int nvme_identify_ns_descs(struct nvme_ctrl *ctrl,
 		goto free_data;
 	}
 
-	for (pos = 0; pos < NVME_IDENTIFY_DATA_SIZE; pos += len) {
-		struct nvme_ns_id_desc *cur = data + pos;
-
+	remain = NVME_IDENTIFY_DATA_SIZE;
+	cur = data;
+	while (remain >= sizeof(*cur)) {
 		if (cur->nidl == 0)
 			break;
+		if (sizeof(*cur) + cur->nidl > remain)
+			break;
 
 		len = nvme_process_ns_desc(ctrl, &info->ids, cur, &csi_seen);
 		if (len < 0)
 			break;
 
 		len += sizeof(*cur);
+		remain -= len;
+		cur += len;
 	}
 
 	if (nvme_multi_css(ctrl) && !csi_seen) {
-- 
2.47.3