From: Ashutosh Desai <ashutoshdesai993@gmail.com> stable inclusion from stable-v5.10.266 commit ef2ecb6cf268debf3890df99fea01b6452dcf78e category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/17183 CVE: CVE-2026-68278 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 55bd5e685bda455b9b50c835f8c8442d52a344a3 ] drm_dp_sideband_append_payload() has three related bugs when processing device-provided sideband reply data: 1. Zero-length curchunk_len underflow: msg_len is a 6-bit field taken directly from the DP sideband header. If a device sends msg_len=0, curchunk_len is set to zero. The condition (curchunk_idx >= curchunk_len) is immediately true, and curchunk_len-1 wraps to 255 (u8 underflow). drm_dp_msg_data_crc4() reads 255 bytes from chunk[48], then memcpy() writes 255 bytes into msg[], both far out of bounds. 2. chunk[48] overflow: curchunk_len can reach 63 (6-bit field). chunk[] is only 48 bytes. Multi-iteration payload assembly appends 16-byte blocks until curchunk_idx reaches curchunk_len, writing up to 15 bytes past the end of chunk[] into msg[]. 3. msg[256] overflow: each chunk contributes (curchunk_len-1) bytes to msg[]. No check ensures curlen + (curchunk_len-1) stays within msg[256], so the memcpy can spill into adjacent struct fields. All three are reachable from any DP MST device that can forge sideband reply messages on a physical connection. Fixes: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper (v0.6)") Cc: <stable@vger.kernel.org> # v3.17+ Signed-off-by: Ashutosh Desai <ashutoshdesai993@gmail.com> Reviewed-by: Lyude Paul <lyude@redhat.com> Signed-off-by: Lyude Paul <lyude@redhat.com> Link: https://patch.msgid.link/20260410041901.2438960-1-ashutoshdesai993@gmail.com Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Hulk Robot <hulkrobot@huawei.com> Signed-off-by: Zhang Hongtao <zhanghongtao35@huawei.com> --- drivers/gpu/drm/drm_dp_mst_topology.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index e71d76daee748..0802ae9a43d0a 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -778,6 +778,12 @@ static bool drm_dp_sideband_append_payload(struct drm_dp_sideband_msg_rx *msg, { u8 crc4; + /* curchunk_len must be >= 1 (min 1 CRC byte) and fit in chunk[] */ + if (!msg->curchunk_len || + msg->curchunk_len > ARRAY_SIZE(msg->chunk) || + msg->curchunk_idx + replybuflen > ARRAY_SIZE(msg->chunk)) + return false; + memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen); msg->curchunk_idx += replybuflen; @@ -788,6 +794,9 @@ static bool drm_dp_sideband_append_payload(struct drm_dp_sideband_msg_rx *msg, print_hex_dump(KERN_DEBUG, "wrong crc", DUMP_PREFIX_NONE, 16, 1, msg->chunk, msg->curchunk_len, false); + /* Guard against accumulated msg[] overflow */ + if (msg->curlen + msg->curchunk_len - 1 > ARRAY_SIZE(msg->msg)) + return false; /* copy chunk into bigger msg */ memcpy(&msg->msg[msg->curlen], msg->chunk, msg->curchunk_len - 1); msg->curlen += msg->curchunk_len - 1; -- 2.43.0