[PATCH v4] 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.

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
v3->v4:
 * Replace do-while with for. A bit exceeded 80 hard limit but still in
   100 soft limit
 * Restore `pos` type. This is subject of another patch if we prefer
   minimalism
---
 drivers/nvme/host/core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f1f719351f3f..253d35937f03 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1540,6 +1540,7 @@ static int nvme_identify_ns_descs(struct nvme_ctrl *ctrl,
 	bool csi_seen = false;
 	int status, pos, len;
 	void *data;
+	struct nvme_ns_id_desc *cur;
 
 	if (ctrl->vs < NVME_VS(1, 3, 0) && !nvme_multi_css(ctrl))
 		return 0;
@@ -1563,11 +1564,14 @@ 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;
+	for (pos = 0; pos < NVME_IDENTIFY_DATA_SIZE - sizeof(*cur); pos += len) {
+		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)
-- 
2.47.3