linux-hardening - [PATCH v2] scsi: libfc: replace deprecated strncpy with memcpy

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Message-ID: <20240221-strncpy-drivers-scsi-libfc-fc_encode-h-v2-1-019a0889c5ca@google.com>
Date: Wed, 21 Feb 2024 23:50:26 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Hannes Reinecke <hare@...e.de>, "James E.J. Bottomley" <jejb@...ux.ibm.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH v2] scsi: libfc: replace deprecated strncpy with memcpy

strncpy() is deprecated [1] and as such we should use different apis to
copy string data.

We can see that ct is NUL-initialized with fc_ct_hdr_fill:
|       ct = fc_ct_hdr_fill(fp, op, sizeof(struct fc_ns_rspn) + len,
...

In fc_ct_hdr_fill():
|       memset(ct, 0, ct_plen);

We also calculate the length of the source string:
|       len = strnlen(fc_host_symbolic_name(lport->host), 255);

...then this argument is used in strncpy(), which is bad because the
pattern of (dest, src, strlen(src)) usually leaves the destination
buffer without NUL-termination. However, it looks as though we do not
require NUL-termination since fr_name is part of a seq_buf-like
structure wherein its length is monitored:
|       struct fc_ns_rspn {
|       	struct fc_ns_fid fr_fid;	/* port ID object */
|       	__u8		fr_name_len;
|       	char		fr_name[];
|       } __attribute__((__packed__));

So, this is really just a byte copy into a length-bounded buffer. Let's
use memcpy().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Changes in v2:
- Don't mark fields with __nonstring
- Link to v1: https://lore.kernel.org/r/20231030-strncpy-drivers-scsi-libfc-fc_encode-h-v1-1-c08c2be6befa@google.com
---
 drivers/scsi/libfc/fc_encode.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/libfc/fc_encode.h b/drivers/scsi/libfc/fc_encode.h
index 7dcac3b6baa7..6b7e4ca6b7b5 100644
--- a/drivers/scsi/libfc/fc_encode.h
+++ b/drivers/scsi/libfc/fc_encode.h
@@ -136,22 +136,24 @@ static inline int fc_ct_ns_fill(struct fc_lport *lport,
 		break;
 
 	case FC_NS_RSPN_ID:
-		len = strnlen(fc_host_symbolic_name(lport->host), 255);
+		len = strnlen(fc_host_symbolic_name(lport->host),
+			      FC_SYMBOLIC_NAME_SIZE);
 		ct = fc_ct_hdr_fill(fp, op, sizeof(struct fc_ns_rspn) + len,
 				    FC_FST_DIR, FC_NS_SUBTYPE);
 		hton24(ct->payload.spn.fr_fid.fp_fid, lport->port_id);
-		strncpy(ct->payload.spn.fr_name,
-			fc_host_symbolic_name(lport->host), len);
+		memcpy(ct->payload.spn.fr_name,
+		       fc_host_symbolic_name(lport->host), len);
 		ct->payload.spn.fr_name_len = len;
 		break;
 
 	case FC_NS_RSNN_NN:
-		len = strnlen(fc_host_symbolic_name(lport->host), 255);
+		len = strnlen(fc_host_symbolic_name(lport->host),
+			      FC_SYMBOLIC_NAME_SIZE);
 		ct = fc_ct_hdr_fill(fp, op, sizeof(struct fc_ns_rsnn) + len,
 				    FC_FST_DIR, FC_NS_SUBTYPE);
 		put_unaligned_be64(lport->wwnn, &ct->payload.snn.fr_wwn);
-		strncpy(ct->payload.snn.fr_name,
-			fc_host_symbolic_name(lport->host), len);
+		memcpy(ct->payload.snn.fr_name,
+		       fc_host_symbolic_name(lport->host), len);
 		ct->payload.snn.fr_name_len = len;
 		break;
 

---
base-commit: 517bc069e3eaad84d879101e0351ca7783243b32
change-id: 20231030-strncpy-drivers-scsi-libfc-fc_encode-h-5ad629f6de9c

Best regards,
--
Justin Stitt <justinstitt@...gle.com>