From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2D5AA3B05AF; Fri, 4 Sep 2026 05:36:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788500187; cv=none; b=ghSGa86Yk858eL4wpsKmyu3EBMdIVV6w7hzY4cpFllCKZBIhPOoMYc8Yh8UCF9kzk2NSt5xfmPgd4gopCvc4Ms+4QWgW7UYIWFSs1ernmiuUXgfpBNBjwDqhYy+hahYeKRPM62v9Mwgi9SeH5AXZmWvqPPr+UFA9TgLeP3HTeXs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788500187; c=relaxed/simple; bh=IPF32lkGfcC2d/24T19Xa+QJFuNm0mbkmVYFcCVDQ70=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NVRzw5UyAH3H/ZPev3Ue7GqcOdwaozI9uygC4BoYuZJ+uvHmRy96Bhik8oDyDB526BX3cyKiqBD1zBkTBhGG2NG2wKLspi6NZgWIAO/8vbZwNTdT03JpqBojHBuWi6DEx2Wn1oRX4nlIip2MkpYFFXXWv9ouklGAA4pHc8M+0oQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=TzQvwWMZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="TzQvwWMZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88B121F00A3D; Fri, 4 Sep 2026 05:36:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788500186; bh=78L7NkR0nGzVBI1F9Hqq6R5LOg3jssnkxCJBsaAM4To=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=TzQvwWMZMw5kA1maD12M5rhDfXiZrrib5n5XDaKbtIAaqc8/UKaT3gZrprBZKq4S8 RzLp2/SG+BB5rjPgnip8cn3ZjF4VEb1ygQWi9uV2zRwtP9Z2SGP5Yxl+gOrLxmHRim 8zzD3C442MVibAJkGavW5aUUvtv5KiE4wM5awuYY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Federico Kirschbaum , Baul Lee , Takashi Iwai Subject: [PATCH 7.2 638/713] ALSA: FCP: do not copy out an uninitialised init response Date: Fri, 4 Sep 2026 07:00:06 +0200 Message-ID: <20260904045818.131390008@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260904045803.810145556@linuxfoundation.org> References: <20260904045803.810145556@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Baul Lee commit 4335e387786479889e6db691fe06d345e52ea536 upstream. fcp_ioctl_init() allocates its response buffer with kmalloc() and copies the whole buffer back to userspace: buf_size = init.step0_resp_size + init.step2_resp_size; void *resp __free(kfree) = kmalloc(buf_size, GFP_KERNEL); ... if (copy_to_user(arg->resp, resp, buf_size)) return -EFAULT; Nothing clears the buffer, and the only writer of its leading step0_resp_size bytes is the step-0 control transfer: err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), FCP_USB_REQ_STEP0, USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN, 0, private->bInterfaceNumber, step0_resp, private->step0_resp_size); if (err < 0) return err; usb_fill_control_urb() does not set URB_SHORT_NOT_OK, so a short or zero-length data stage completes with status 0 and snd_usb_ctl_msg() returns a small actual_length. The only check is err < 0, so a short transfer is accepted as success. snd_usb_ctl_msg() copies the full size back unconditionally: buf = kmemdup(data, size, GFP_KERNEL); ... memcpy(data, buf, size); Bytes the device never wrote are therefore restored into resp unchanged and copied to userspace. step0_resp_size and step2_resp_size are each validated only to 1..255, so the caller also picks the slab cache, from kmalloc-8 up to kmalloc-512. On 7.2.0-rc5 (arm64), device answering step 0 with a zero-length data stage, s0 = s2 = 255: # init_on_alloc off, no spray step0 window [0,255): nonzero=94/255 000: 00 80 60 06 00 00 ff ff 18 00 00 00 57 01 ea 01 010: 08 78 22 13 00 00 ff ff a8 c4 5f 80 00 80 ff ff # same kernel, kmalloc-512 pre-seeded with an 8-byte tag step0 window [0,255): nonzero=219/255 tagbytes=232 # identical run, init_on_alloc=1 step0 window [0,255): nonzero=0/255 tagbytes=0 # all three runs step2 window [255,510): device words matched=62/62 a8 c4 5f 80 00 80 ff ff is the little-endian kernel text address ffff8000805fc4a8. The step-2 window is unaffected, so the disclosure is exactly the step-0 region. Zero the buffer, and require the step-0 transfer to deliver the full step0_resp_size bytes so a short data stage is reported as an error. Discovered by XBOW, triaged by Baul Lee Fixes: 46757a3e7d50 ("ALSA: FCP: Add Focusrite Control Protocol driver") Reported-by: Federico Kirschbaum Reported-by: Baul Lee Cc: stable@vger.kernel.org Signed-off-by: Baul Lee Link: https://patch.msgid.link/20260805013804.38839-1-baul.lee@xbow.com Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/usb/fcp.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/sound/usb/fcp.c +++ b/sound/usb/fcp.c @@ -494,7 +494,7 @@ static int fcp_ioctl_init(struct usb_mix buf_size = init.step0_resp_size + init.step2_resp_size; void *resp __free(kfree) = - kmalloc(buf_size, GFP_KERNEL); + kzalloc(buf_size, GFP_KERNEL); if (!resp) return -ENOMEM; @@ -1033,6 +1033,8 @@ static int fcp_init(struct usb_mixer_int step0_resp, private->step0_resp_size); if (err < 0) return err; + if (err != private->step0_resp_size) + return -EIO; err = fcp_init_notify(mixer); if (err < 0)