scsi: target: core: Fix iSCSI ISID use-after-free in REGISTER AND MOVE

core_scsi3_emulate_pro_register_and_move() maps the PERSISTENT RESERVE OUT
parameter list with transport_kmap_data_sg() and parses the destination
TransportID with target_parse_pr_out_transport_id(). For an iSCSI
TransportID (FORMAT CODE 01b), iscsi_parse_pr_out_transport_id() returns
the ISID in iport_ptr as a raw pointer into that mapped buffer.

The function then unmaps the buffer with transport_kunmap_data_sg() before
dereferencing iport_ptr in strcmp(), __core_scsi3_locate_pr_reg() and
core_scsi3_alloc_registration(). When the parameter list spans more than
one page (PARAMETER LIST LENGTH > 4096), transport_kmap_data_sg() uses
vmap() and transport_kunmap_data_sg() does vunmap(), so the kernel virtual
address backing iport_ptr is torn down and every subsequent dereference is
a use-after-free read of the unmapped region.

Keep the parameter list mapped until iport_ptr is no longer needed: drop
the early transport_kunmap_data_sg() and unmap once on the success path,
right before returning. The error paths already unmap through the existing
"if (buf) transport_kunmap_data_sg(cmd)" at the out: label, which now runs
on every post-map error exit because buf is no longer cleared early. Only
reads of the mapping happen while spinlocks are held; the map and unmap
calls remain outside any lock. The sibling caller
core_scsi3_decode_spec_i_port() already uses the buffer before unmapping it
and is left unchanged.

Fixes: 4949314c72 ("target: Allow control CDBs with data > 1 page")
Cc: [email protected]
Signed-off-by: Bryam Vargas <[email protected]>
Reviewed-by: John Garry <[email protected]>
Reviewed-by: David Disseldorp <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>

drivers/target/target_core_pr.c

@@ -3293,9 +3293,6 @@ core_scsi3_emulate_pro_register_and_move(struct se_cmd *cmd, u64 res_key,
 		goto out;
 	}
 
-	transport_kunmap_data_sg(cmd);
-	buf = NULL;
-
 	pr_debug("SPC-3 PR [%s] Extracted initiator %s identifier: %s"
 		" %s\n", dest_tf_ops->fabric_name, (iport_ptr != NULL) ?
 		"port" : "device", initiator_str, (iport_ptr != NULL) ?
@@ -3532,6 +3529,11 @@ after_iport_check:
 	core_scsi3_update_and_write_aptpl(cmd->se_dev, aptpl);
 
 	core_scsi3_put_pr_reg(dest_pr_reg);
+	/*
+	 * iport_ptr aliases the PR-OUT parameter list mapped above, so the
+	 * buffer is unmapped only here on success (and at out: on error).
+	 */
+	transport_kunmap_data_sg(cmd);
 	return 0;
 out:
 	if (buf)