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:
- 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.
- 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[].
- 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.