CVE-2026-80827: USB: serial: option: fix slab OOB read in interrupt URB callback

CVE-2026-80827: USB: serial: option: fix slab OOB read in interrupt URB callback

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

USB: serial: option: fix slab OOB read in interrupt URB callback

The interrupt URB buffer is allocated in setup_port_interrupt_in() based
on the endpoint's wMaxPacketSize:

    buffer_size = usb_endpoint_maxp(epd);
    port->interrupt_in_buffer = kmalloc(buffer_size, GFP_KERNEL);

When a USB device declares wMaxPacketSize = 8 on its interrupt IN
endpoint, the buffer is allocated from kmalloc-8 cache (exactly
8 bytes).

If the device sends a short packet (actual_length < wMaxPacketSize),
the URB completes with status == 0 and the callback proceeds to read:

    data[sizeof(struct usb_ctrlrequest)]

which evaluates to data[8], accessing 1 byte beyond the allocated 8-byte
buffer. This results in a slab out-of-bounds read.

Fix this by adding the missing bounds check: first verify that the
actual length is large enough to contain the struct usb_ctrlrequest
header before accessing req_pkt->bRequestType and req_pkt->bRequest,
and then verify that there is an additional byte for the modem signal
state before reading data[sizeof(struct usb_ctrlrequest)] inside the
conditional.  Use sizeof(*req_pkt) instead of sizeof(struct
usb_ctrlrequest) for consistency.

[ johan: use dev_err(); split signals declaration and initialisation ]

The Linux kernel CVE team has assigned CVE-2026-80827 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 5.10.269 with commit fbe60fd2abc8a5561f39719a41ad9a01b5d8e567
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 5.15.220 with commit 94e5525697b9e91ddc4071129874120a50a4f342
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 6.1.187 with commit 6b8cf5422c7e96ed5b22a8368eff663f3f98b8ec
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 6.6.156 with commit 030e3a73d3c3aa67c44454649e984d6383cdb7d3
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 6.12.108 with commit 060db7d48af1e650643c8b8319111a9ea2ce4486
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 6.18.49 with commit 2ef5560387f2c0713cee975be2b24b281bd90f3e
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 7.1.13 with commit a72a13c83a652516a0e469d275b81d29a7429049
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 7.2.3 with commit d762aef4eba354066be21a5d88eb2066e282f4c9
	Issue introduced in 2.6.12 with commit 58cfe9113e485f7e04bd0eac4fc4251b330af501 and fixed in 7.3-rc1 with commit 885d802f544ca7bfa8f3984d94233cce715bb6b3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80827
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/usb/serial/option.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/fbe60fd2abc8a5561f39719a41ad9a01b5d8e567
	https://git.kernel.org/stable/c/94e5525697b9e91ddc4071129874120a50a4f342
	https://git.kernel.org/stable/c/6b8cf5422c7e96ed5b22a8368eff663f3f98b8ec
	https://git.kernel.org/stable/c/030e3a73d3c3aa67c44454649e984d6383cdb7d3
	https://git.kernel.org/stable/c/060db7d48af1e650643c8b8319111a9ea2ce4486
	https://git.kernel.org/stable/c/2ef5560387f2c0713cee975be2b24b281bd90f3e
	https://git.kernel.org/stable/c/a72a13c83a652516a0e469d275b81d29a7429049
	https://git.kernel.org/stable/c/d762aef4eba354066be21a5d88eb2066e282f4c9
	https://git.kernel.org/stable/c/885d802f544ca7bfa8f3984d94233cce715bb6b3