CVE-2026-63887

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

scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf

iscsi_encode_text_output() concatenates key=value0 records into login->rsp_buf, an 8192-byte kzalloc(MAX_KEY_VALUE_PAIRS) buffer allocated in iscsit_alloc_login_setup_buffer(). The three sprintf() call sites in this function (lines 1398, 1411, 1424 in v7.1-rc2) never check the remaining buffer capacity:

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

The 8192-byte ceiling at iscsi_target_check_login_request() bounds the input Login PDU payload, but a single PDU can carry up to 2048 minimal four-byte a=b0 pairs, each unknown key expanding to a 16-byte a=NotUnderstood0 output record via iscsi_add_notunderstood_response(). 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 iscsi_encode_text_record() helper that uses snprintf() with a per-call bounds check against the remaining buffer, and threads a u32 textbuf_size parameter through iscsi_encode_text_output(). Both call sites in iscsi_target_handle_csg_zero() (PHASE_SECURITY) and iscsi_target_handle_csg_one() (PHASE_OPERATIONAL) pass MAX_KEY_VALUE_PAIRS. On overflow the encoder logs the condition, calls iscsi_release_extra_responses() to drop queued records, and returns -1; both caller sites now emit ISCSI_STATUS_CLS_INITIATOR_ERR / ISCSI_LOGIN_STATUS_INIT_ERR via iscsit_tx_login_rsp() before returning, so the initiator sees an explicit failed-login response rather than a silent connection drop. (Prior to this patch only the PHASE_OPERATIONAL caller did that; the PHASE_SECURITY caller is converted to the same shape.)

Affected Software

References

• https://git.kernel.org/stable/c/26e4a304b7e6f1338c675d527608d32549c091db
• https://git.kernel.org/stable/c/30bf335e8fe170322080ee001f05ca29c50680b3
• https://git.kernel.org/stable/c/4e9f0c4a645c995bc75c06c7b3644254ffb4c76b
• https://git.kernel.org/stable/c/594a40360012ce5f94c715d5e3b20fa3af7d525a
• https://git.kernel.org/stable/c/b19382dfc6e7dee6d3859ba44b6ca29e97a51627
• https://git.kernel.org/stable/c/bf33e01f88388c43e285492a63e539df6ffed64c
• https://git.kernel.org/stable/c/cb84e974fb172bc71386289f37b78ea679410b39
• https://git.kernel.org/stable/c/efe633e600a0ac68357206fede21b1ac8178f3b8