cdc_ncm_rx_verify_ndp16() validates that the NDP header and its DPE entries fit within the skb. The first check correctly accounts for ndpoffset: if ((ndpoffset + sizeof(struct usb_cdc_ncm_ndp16)) > skb_in->len) but the second check omits it: if ((sizeof(struct usb_cdc_ncm_ndp16) + ret * (sizeof(struct usb_cdc_ncm_dpe16))) > skb_in->len) This validates the DPE array size against the total skb length as if the NDP were at offset 0, rather than at ndpoffset. When the NDP is placed near the end of the NTB (large wNdpIndex), the DPE entries can extend past the skb data buffer even though the check passes. cdc_ncm_rx_fixup() then reads out-of-bounds memory when iterating the DPE array. Add ndpoffset to the nframes bounds check and use struct_size_t() to express the NDP-plus-DPE-array size more clearly. Found by coverage-guided fuzzing with QEMU system-mode emulation. Fixes: ff06ab13a4cc ("net: cdc_ncm: splitting rx_fixup for code reuse") Signed-off-by: Tobi Gaertner --- drivers/net/usb/cdc_ncm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c index 5d123df0a..846f8b997 100644 --- a/drivers/net/usb/cdc_ncm.c +++ b/drivers/net/usb/cdc_ncm.c @@ -1675,8 +1675,8 @@ int cdc_ncm_rx_verify_ndp16(struct sk_buff *skb_in, int ndpoffset) sizeof(struct usb_cdc_ncm_dpe16)); ret--; /* we process NDP entries except for the last one */ - if ((sizeof(struct usb_cdc_ncm_ndp16) + - ret * (sizeof(struct usb_cdc_ncm_dpe16))) > skb_in->len) { + if (ndpoffset + struct_size_t(struct usb_cdc_ncm_ndp16, + dpe16, ret) > skb_in->len) { netif_dbg(dev, rx_err, dev->net, "Invalid nframes = %d\n", ret); ret = -EINVAL; } -- 2.43.0