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 E3662377A82; Thu, 20 Aug 2026 16:34:15 +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=1787243657; cv=none; b=TPIkHRylQBQM3Df1TdlMbUDZpO8rf4+CDjtLuRA4MzoRv9KpkWcQj+ZYJFVJz9iixm6Xz/iEbRxZIrs5dv0y4M9bXs4wD1DVAo975j0huniV5MmEeTAFGDIzxc+Kf6ynUo9v8AghOo9B7KBifVg4CplNUGFysESUeZN1GJNHCZ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787243657; c=relaxed/simple; bh=YpjuuOuk5Ia26qMFEgTrmMVlTzfdC5QKpnP7TEwJRiI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=sz7IK3Vmy8SvWyS5B4N7NlV0Y9jNiomXidXHTvQTBfbgea5cfjytKY4tJiK0GEA4Z5c+4nkcDucFWnTjlYQZ/wxRepIo5N8DsbQ0sSqf4fyJsI+KR/0oS+yDYtFGkffQ37m/xLtFSX1Pr2ywv4qudADx3MbREy//j09rsz6Eu7A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=1hvpW9+o; 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="1hvpW9+o" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A8131F000E9; Thu, 20 Aug 2026 16:34:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1787243655; bh=OR5cWi+eFkaBjmJvCW7Jvpl7DLx2bYxkFaRuAtKMG9o=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=1hvpW9+oqWD2lbkLBDDAlAA9ZSSnlMglG6cnHuZy14nRzLG1wL94HpVWyyve/vVO/ FWk9XYoKrbp+nSCyGQdtbaZCYHzFOMLZSY43GUlvb1uu57xvrVAGihKYPlSAe2t+ap 3RM8gBNvc/VniKYQaFI0xHnJKx9VH1VCVfcUsSVA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ashutosh Desai , Lyude Paul , Sasha Levin Subject: [PATCH 5.15 171/272] drm/dp/mst: fix OOB reads on 2-byte fields in sideband reply parsers Date: Thu, 20 Aug 2026 16:55:55 +0200 Message-ID: <20260820145236.498244122@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260820145231.229664293@linuxfoundation.org> References: <20260820145231.229664293@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ashutosh Desai [ Upstream commit 6b89ba3dba2f583626fb693e47e951ffb8bf591f ] Three sideband reply parsers read 16-bit fields as: val = (raw->msg[idx] << 8) | (raw->msg[idx+1]); and check bounds only after the fact. When idx == raw->curlen, raw->msg[idx+1] reads one byte past the received message data into the following struct fields (curchunk_len, curchunk_idx, curlen). Affected functions: - drm_dp_sideband_parse_enum_path_resources_ack() full_payload_bw_number and avail_payload_bw_number fields - drm_dp_sideband_parse_allocate_payload_ack() allocated_pbn field - drm_dp_sideband_parse_query_payload_ack() allocated_pbn field Fix by using a single combined check (idx + 2 > curlen) before each 2-byte read. Since the check is strictly tighter than idx > curlen, no separate step is needed. Fixes: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper (v0.6)") Cc: # v3.17+ Signed-off-by: Ashutosh Desai Reviewed-by: Lyude Paul [added fixes tag] Signed-off-by: Lyude Paul Link: https://patch.msgid.link/20260510203128.2884846-1-ashutoshdesai993@gmail.com Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/drm_dp_mst_topology.c | 17 ++++------------- 1 file changed, 4 insertions(+), 13 deletions(-) --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -924,16 +924,13 @@ static bool drm_dp_sideband_parse_enum_p repmsg->u.path_resources.port_number = (raw->msg[idx] >> 4) & 0xf; repmsg->u.path_resources.fec_capable = raw->msg[idx] & 0x1; idx++; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; repmsg->u.path_resources.full_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]); idx += 2; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; repmsg->u.path_resources.avail_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]); - idx += 2; - if (idx > raw->curlen) - goto fail_len; return true; fail_len: DRM_DEBUG_KMS("enum resource parse length fail %d %d\n", idx, raw->curlen); @@ -951,12 +948,9 @@ static bool drm_dp_sideband_parse_alloca goto fail_len; repmsg->u.allocate_payload.vcpi = raw->msg[idx]; idx++; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; repmsg->u.allocate_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx+1]); - idx += 2; - if (idx > raw->curlen) - goto fail_len; return true; fail_len: DRM_DEBUG_KMS("allocate payload parse length fail %d %d\n", idx, raw->curlen); @@ -970,12 +964,9 @@ static bool drm_dp_sideband_parse_query_ repmsg->u.query_payload.port_number = (raw->msg[idx] >> 4) & 0xf; idx++; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; repmsg->u.query_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]); - idx += 2; - if (idx > raw->curlen) - goto fail_len; return true; fail_len: DRM_DEBUG_KMS("query payload parse length fail %d %d\n", idx, raw->curlen);