[PATCH] usb: gadget: f_ncm: validate datagram bounds in ncm_unwrap_ntb()

[Sonali Pradhan]

When unpacking host-supplied NTBs, ncm_unwrap_ntb() checks datagram length
against frame_max but does not verify that the datagram fits within the
declared block length. Additionally, when decoding multiple NTBs from a
single socket buffer, subsequent block lengths are not checked against the
actual remaining buffer data.

With these checks missing, a malicious USB host can specify datagram
offsets and lengths that point beyond the block, or supply secondary NTB
headers declaring lengths larger than the buffer. skb_put_data() then
copies adjacent kernel memory from skb_shared_info into the network skb.

Fix this by verifying that sufficient buffer space remains for the NTB
header before parsing, handling zero-length block declarations, ensuring
that block lengths never exceed the remaining buffer space, and verifying
that each datagram payload stays strictly within the block boundary.

Fixes: 427694cfaafa ("usb: gadget: ncm: Handle decoding of multiple NTB's in unwrap call")
Fixes: 2b74b0a04d3e ("USB: gadget: f_ncm: add bounds checks to ncm_unwrap_ntb()")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: Jetski:Gemini-2.5-Pro
Signed-off-by: Sonali Pradhan <sonalipradhan@xxxxxxxxxx>
---
 drivers/usb/gadget/function/f_ncm.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index c5bf8a448d64..64eabda2f546 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -1189,6 +1189,10 @@ static int ncm_unwrap_ntb(struct gether *port,
 	frame_max = ncm_opts->max_segment_size;
 
 parse_ntb:
+	if (to_process < (int)opts->nth_size) {
+		INFO(port->func.config->cdev, "Packet too small for headers\n");
+		goto err;
+	}
 	tmp = (__le16 *)ntb_ptr;
 
 	/* dwSignature */
@@ -1209,8 +1213,12 @@ static int ncm_unwrap_ntb(struct gether *port,
 	tmp++; /* skip wSequence */
 
 	block_len = get_ncm(&tmp, opts->block_length);
+	if (block_len == 0)
+		block_len = to_process;
+
 	/* (d)wBlockLength */
-	if ((block_len < opts->nth_size + opts->ndp_size) || (block_len > ntb_max)) {
+	if ((block_len < opts->nth_size + opts->ndp_size) || (block_len > ntb_max) ||
+			(block_len > to_process)) {
 		INFO(port->func.config->cdev, "Bad block length: %#X\n", block_len);
 		goto err;
 	}
@@ -1273,7 +1281,7 @@ static int ncm_unwrap_ntb(struct gether *port,
 			index = index2;
 			/* wDatagramIndex[0] */
 			if ((index < opts->nth_size) ||
-					(index > block_len - opts->dpe_size)) {
+					(index > block_len)) {
 				INFO(port->func.config->cdev,
 				     "Bad index: %#X\n", index);
 				goto err;
@@ -1285,7 +1293,8 @@ static int ncm_unwrap_ntb(struct gether *port,
 			 * ethernet hdr + crc or larger than max frame size
 			 */
 			if ((dg_len < 14 + crc_len) ||
-					(dg_len > frame_max)) {
+					(dg_len > frame_max) ||
+					(dg_len > block_len - index)) {
 				INFO(port->func.config->cdev,
 				     "Bad dgram length: %#X\n", dg_len);
 				goto err;
@@ -1310,7 +1319,7 @@ static int ncm_unwrap_ntb(struct gether *port,
 			dg_len2 = get_ncm(&tmp, opts->dgram_item_len);
 
 			/* wDatagramIndex[1] */
-			if (index2 > block_len - opts->dpe_size) {
+			if (index2 > block_len) {
 				INFO(port->func.config->cdev,
 				     "Bad index: %#X\n", index2);
 				goto err;
-- 
2.55.0.rc0.799.gd6f94ed593-goog