CVE-2026-63887: scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf

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

scsi: target: iscsi: Bound iscsiencodetextoutput() appends to rspbuf

iscsiencodetextoutput() concatenates "key=value\0" records into login->rspbuf, an 8192-byte kzalloc(MAXKEYVALUEPAIRS) buffer allocated in iscsitallocloginsetupbuffer(). The three sprintf() call sites in this function (lines 1398, 1411, 1424 in v7.1-rc2) never check the remaining buffer capacity:

length += sprintf(outputbuf, "%s=%s", er->key, er->value); length += 1; outputbuf = textbuf + length;

The 8192-byte ceiling at iscsitargetcheckloginrequest() bounds the input Login PDU payload, but a single PDU can carry up to 2048 minimal four-byte "a=b\0" pairs, each unknown key expanding to a 16-byte "a=NotUnderstood\0" output record via iscsiaddnotunderstoodresponse(). 2048 16 = 32 KiB of output into an 8 KiB buffer, producing a ~24 KiB heap overrun in the kmalloc-8k slab.

The fix introduces a static iscsiencodetextrecord() helper that uses snprintf() with a per-call bounds check against the remaining buffer, and threads a u32 textbufsize parameter through iscsiencodetextoutput(). Both call sites in iscsitargethandlecsgzero() (PHASESECURITY) and iscsitargethandlecsgone() (PHASEOPERATIONAL) pass MAXKEYVALUEPAIRS. On overflow the encoder logs the condition, calls iscsireleaseextraresponses() to drop queued records, and returns -1; both caller sites now emit ISCSISTATUSCLSINITIATORERR / ISCSILOGINSTATUSINITERR via iscsittxloginrsp() before returning, so the initiator sees an explicit failed-login response rather than a silent connection drop. (Prior to this patch only the PHASEOPERATIONAL caller did that; the PHASESECURITY caller is converted to the same shape.)