[PATCH v3] 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 checking (header size + .nidl) against
remaining buffer length.

Also small minor related fix: `pos` should be unsigned size_t,
not signed int.

Signed-off-by: Eugene Korenevsky <ekorenevsky@aliyun.com>
---
v1->v2:
 * Simplification: do not touch nvme_process_ns_desc()
 * Update commit description
v2->v3:
 * Even more simplification
 * Replace while with do-while as first pre-loop condition
   check is pointless
 * Change `pos` type: int -> size_t
 * Update commit description
---
 drivers/nvme/host/core.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f1f719351f3f..73263545e3cd 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1538,8 +1538,10 @@ 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;
+	size_t pos;
 	void *data;
+	struct nvme_ns_id_desc *cur;
 
 	if (ctrl->vs < NVME_VS(1, 3, 0) && !nvme_multi_css(ctrl))
 		return 0;
@@ -1563,18 +1565,23 @@ 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;
+	pos = 0;
+	do {
+		cur = data + pos;
 
 		if (cur->nidl == 0)
 			break;
+		/* check ns id desc does not exceed remaining buffer by size */
+		if (cur->nidl + sizeof(*cur) > NVME_IDENTIFY_DATA_SIZE - pos)
+			break;
 
 		len = nvme_process_ns_desc(ctrl, &info->ids, cur, &csi_seen);
 		if (len < 0)
 			break;
 
-		len += sizeof(*cur);
-	}
+		pos += sizeof(*cur);
+		pos += len;
+	} while (pos < NVME_IDENTIFY_DATA_SIZE - sizeof(*cur));
 
 	if (nvme_multi_css(ctrl) && !csi_seen) {
 		dev_warn(ctrl->device, "Command set not reported for nsid:%d\n",
-- 
2.47.3