From 1febec7e47cdcd01f43fb0211094e3010474666e Mon Sep 17 00:00:00 2001 From: Sonali Pradhan Date: Fri, 3 Jul 2026 08:37:24 +0000 Subject: [PATCH] usb: gadget: f_ncm: validate datagram bounds in ncm_unwrap_ntb() 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 Assisted-by: Jetski:Gemini-2.5-Pro Signed-off-by: Sonali Pradhan Link: https://patch.msgid.link/20260703083725.1903850-1-sonalipradhan@google.com Signed-off-by: Greg Kroah-Hartman --- 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;