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Thu, 09 Apr 2026 21:00:34 -0700 (PDT) Received: from TDC4045031631.e0cglfehwr0e5gttmepj3hi3hf.ux.internal.cloudapp.net ([20.63.37.123]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8ac84cdda1csm14132946d6.43.2026.04.09.21.00.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 21:00:33 -0700 (PDT) From: Ashutosh Desai To: dri-devel@lists.freedesktop.org Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, linux-kernel@vger.kernel.org, Ashutosh Desai Subject: [PATCH] drm/dp/mst: fix OOB reads on 2-byte fields in sideband reply parsers Date: Fri, 10 Apr 2026 04:00:26 +0000 Message-Id: <20260410040026.2436280-1-ashutoshdesai993@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Three sideband reply parsers read 16-bit fields as: val =3D (raw->msg[idx] << 8) | (raw->msg[idx+1]); and only check bounds after the fact (idx +=3D 2, then if (idx > raw->curlen)). When idx =3D=3D raw->curlen at the point of the read, raw->msg[idx+1] is one byte past the received message data, reading 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 Move the bounds check to immediately before each 2-byte read, using idx + 2 > raw->curlen, consistent with the fix pattern used elsewhere in this file. Signed-off-by: Ashutosh Desai --- drivers/gpu/drm/display/drm_dp_mst_topology.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/dr= m/display/drm_dp_mst_topology.c index 9cef6c576..f2a7dbc5e 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -931,14 +931,13 @@ static bool drm_dp_sideband_parse_enum_path_resources= _ack(struct drm_dp_sideband idx++; if (idx > raw->curlen) goto fail_len; + if (idx + 2 > raw->curlen) + goto fail_len; repmsg->u.path_resources.full_payload_bw_number =3D (raw->msg[idx] << 8) = | (raw->msg[idx+1]); idx +=3D 2; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; repmsg->u.path_resources.avail_payload_bw_number =3D (raw->msg[idx] << 8)= | (raw->msg[idx+1]); - idx +=3D 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= ); @@ -958,10 +957,9 @@ static bool drm_dp_sideband_parse_allocate_payload_ack= (struct drm_dp_sideband_ms idx++; if (idx > raw->curlen) goto fail_len; - repmsg->u.allocate_payload.allocated_pbn =3D (raw->msg[idx] << 8) | (raw-= >msg[idx+1]); - idx +=3D 2; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; + repmsg->u.allocate_payload.allocated_pbn =3D (raw->msg[idx] << 8) | (raw-= >msg[idx+1]); return true; fail_len: DRM_DEBUG_KMS("allocate payload parse length fail %d %d\n", idx, raw->cur= len); @@ -977,10 +975,9 @@ static bool drm_dp_sideband_parse_query_payload_ack(st= ruct drm_dp_sideband_msg_r idx++; if (idx > raw->curlen) goto fail_len; - repmsg->u.query_payload.allocated_pbn =3D (raw->msg[idx] << 8) | (raw->ms= g[idx + 1]); - idx +=3D 2; - if (idx > raw->curlen) + if (idx + 2 > raw->curlen) goto fail_len; + repmsg->u.query_payload.allocated_pbn =3D (raw->msg[idx] << 8) | (raw->ms= g[idx + 1]); return true; fail_len: DRM_DEBUG_KMS("query payload parse length fail %d %d\n", idx, raw->curlen= ); --=20 2.34.1