CVE-2026-68278drm/dp/mst: fix buffer overflows in sideband chunk accumulation

Official description

In the Linux kernel, the following vulnerability has been resolved: drm/dp/mst: fix buffer overflows in sideband chunk accumulation 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ef2ecb6cf268debf3890df99fea01b6452dcf78e
• https://git.kernel.org/stable/c/d4e05dedb252ed3e540a0c9be511e427f098110a
• https://git.kernel.org/stable/c/4d5109075a787de28c9e89940f9dee45269f91fa
• https://git.kernel.org/stable/c/53937a2787d29c7a460e984dc4f20ff6ac91dc65
• https://git.kernel.org/stable/c/ef0dbcc200c3389f1f781ab181932a97e54b51af
• https://git.kernel.org/stable/c/1e5827839ad0ceb0079d1560c321fa3656b54f21
• https://git.kernel.org/stable/c/a6366b551079c79bf7bdbadd74c97358bcfe2d58
• https://git.kernel.org/stable/c/55bd5e685bda455b9b50c835f8c8442d52a344a3