From 04a9508e07582f553e9ea767f9e4a9b93839914b Mon Sep 17 00:00:00 2001 From: MarkLee131 Date: Sat, 25 Apr 2026 18:33:17 +0800 Subject: [PATCH] descriptor: Fix two memory-safety bugs in malformed config descriptor handling Two issues reachable from a malformed config descriptor returned by an attached USB device, both surfaced by the same libFuzzer + ASan run. 1) parse_interface() reads bNumEndpoints from the interface descriptor and increments usb_interface->num_altsetting before entering the inner loop that skips class/vendor specific descriptors ahead of the endpoint array. If that loop's bLength > size short-read branch fires, the function returns before the endpoint array is allocated, leaving the caller with bNumEndpoints > 0 and endpoint == NULL. libusb.h documents endpoint as an array sized by bNumEndpoints, and the testlibusb and xusb examples both iterate it accordingly, so a NULL deref follows. Reset bNumEndpoints to 0 before returning so the invariant holds. 2) The first-pass loop in parse_iad_array() compares header.bLength against the original size argument instead of the remaining bytes, so a single descriptor with bLength == size - 1 lets consumed reach size - 1 and the next iteration enters with only one byte of buffer left. The buf[1] read on the second line of the loop body lands one byte past the malloc allocation that backs the descriptor data. The sibling parsers parse_configuration() and parse_interface() in the same file already use the remaining-bytes form. Switch the IAD parser loop guard and bound check to match. Both code paths are reachable from public APIs (libusb_get_*_config_descriptor and libusb_get_*_interface_association_descriptors), with the malformed input supplied by the attached device. Minimal reproducers are 20 and 9 bytes respectively. Fixes #1813 CVE: CVE-2026-23679 CVE-2026-47104 Upstream-Status: Backport [https://github.com/libusb/libusb/commit/bc0886173ea15b8cc9bba2918f58a97a7f185231] Backport Changes: - The upstream version_nano.h bump is omitted because this is a security backport to libusb 1.0.29, not a version upgrade. Signed-off-by: MarkLee131 (cherry picked from commit bc0886173ea15b8cc9bba2918f58a97a7f185231) Signed-off-by: Anil Dongare --- libusb/descriptor.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/libusb/descriptor.c b/libusb/descriptor.c index 870883a..7d4f118 100644 --- a/libusb/descriptor.c +++ b/libusb/descriptor.c @@ -241,6 +241,10 @@ static int parse_interface(libusb_context *ctx, usbi_warn(ctx, "short extra intf desc read %d/%u", size, header->bLength); + /* Keep the invariant: bNumEndpoints > 0 implies + * endpoint != NULL. The endpoint array isn't + * allocated yet on this early return. */ + ifp->bNumEndpoints = 0; return parsed; } @@ -1365,7 +1369,7 @@ static int parse_iad_array(struct libusb_context *ctx, /* First pass: Iterate through desc list, count number of IADs */ iad_array->length = 0; - while (consumed < size) { + while (size - consumed >= DESC_HEADER_LENGTH) { header.bLength = buf[0]; header.bDescriptorType = buf[1]; if (header.bLength < DESC_HEADER_LENGTH) { @@ -1373,9 +1377,9 @@ static int parse_iad_array(struct libusb_context *ctx, header.bLength); return LIBUSB_ERROR_IO; } - else if (header.bLength > size) { + else if (header.bLength > size - consumed) { usbi_warn(ctx, "short config descriptor read %d/%u", - size, header.bLength); + size - consumed, header.bLength); return LIBUSB_ERROR_IO; } if (header.bDescriptorType == LIBUSB_DT_INTERFACE_ASSOCIATION) -- 2.51.0