CVE-2026-74556: scsi: libiscsi_tcp: Bound SCSI Response data segment to the connection buffer

In the Linux kernel, the following vulnerability has been resolved:

scsi: libiscsitcp: Bound SCSI Response data segment to the connection buffer

iscsitcphdrdissect() receives the data segment of several PDU types into the fixed-size conn->data buffer, which is allocated for ISCSIDEFMAXRECVSEGLEN (8192) bytes. For the LOGINRSP, TEXTRSP, REJECT and ASYNCEVENT opcodes the dissect path already rejects a PDU whose DataSegmentLength exceeds that buffer.

The SCSI Command Response (ISCSIOPSCSICMDRSP) path also copies its data segment (sense/response data) into conn->data via iscsitcpdatarecvprep(), but it does so without the same check. The only upstream bound on in.datalen is conn->maxrecvdlength, the initiator's advertised MaxRecvDataSegmentLength, which is commonly negotiated well above 8192 (open-iscsi defaults to 262144). A target that returns a SCSI Response with a DataSegmentLength between 8193 and maxrecvdlength therefore overflows the 8192-byte conn->data buffer.

Once the same bound applies, ISCSIOPSCSICMDRSP is handled exactly like those responses: bound the data segment, receive it into conn->data when present, and otherwise complete the PDU with no data. Fold the opcode into that case group rather than duplicating the check.