linux-hardening - [PATCH] scsi: ibmvfc: replace deprecated strncpy with strscpy

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Message-ID: <20231030-strncpy-drivers-scsi-ibmvscsi-ibmvfc-c-v1-1-5a4909688435@google.com>
Date: Mon, 30 Oct 2023 19:04:33 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Tyrel Datwyler <tyreld@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, 
	Nicholas Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	"James E.J. Bottomley" <jejb@...ux.ibm.com>, "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] scsi: ibmvfc: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect these fields to be NUL-terminated as the property names from
which they are derived are also NUL-terminated.

Moreover, NUL-padding is not required as our destination buffers are
already NUL-allocated and any future NUL-byte assignments are redundant
(like the ones that strncpy() does).
ibmvfc_probe() ->
|       struct ibmvfc_host *vhost;
|       struct Scsi_Host *shost;
...
| 	shost = scsi_host_alloc(&driver_template, sizeof(*vhost));
... **side note: is this a bug? Looks like a type to me   ^^^^^**
...
|	vhost = shost_priv(shost);

... where shost_priv() is:
|       static inline void *shost_priv(struct Scsi_Host *shost)
|       {
|       	return (void *)shost->hostdata;
|       }

.. and:
scsi_host_alloc() ->
| 	shost = kzalloc(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL);

And for login_info->..., NUL-padding is also not required as it is
explicitly memset to 0:
|	memset(login_info, 0, sizeof(*login_info));

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/scsi/ibmvscsi/ibmvfc.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
index ce9eb00e2ca0..e73a39b1c832 100644
--- a/drivers/scsi/ibmvscsi/ibmvfc.c
+++ b/drivers/scsi/ibmvscsi/ibmvfc.c
@@ -1455,7 +1455,7 @@ static void ibmvfc_gather_partition_info(struct ibmvfc_host *vhost)
 
 	name = of_get_property(rootdn, "ibm,partition-name", NULL);
 	if (name)
-		strncpy(vhost->partition_name, name, sizeof(vhost->partition_name));
+		strscpy(vhost->partition_name, name, sizeof(vhost->partition_name));
 	num = of_get_property(rootdn, "ibm,partition-no", NULL);
 	if (num)
 		vhost->partition_number = *num;
@@ -1498,13 +1498,15 @@ static void ibmvfc_set_login_info(struct ibmvfc_host *vhost)
 	login_info->async.va = cpu_to_be64(vhost->async_crq.msg_token);
 	login_info->async.len = cpu_to_be32(async_crq->size *
 					    sizeof(*async_crq->msgs.async));
-	strncpy(login_info->partition_name, vhost->partition_name, IBMVFC_MAX_NAME);
-	strncpy(login_info->device_name,
-		dev_name(&vhost->host->shost_gendev), IBMVFC_MAX_NAME);
+	strscpy(login_info->partition_name, vhost->partition_name,
+		sizeof(login_info->partition_name));
+
+	strscpy(login_info->device_name,
+		dev_name(&vhost->host->shost_gendev), sizeof(login_info->device_name));
 
 	location = of_get_property(of_node, "ibm,loc-code", NULL);
 	location = location ? location : dev_name(vhost->dev);
-	strncpy(login_info->drc_name, location, IBMVFC_MAX_NAME);
+	strscpy(login_info->drc_name, location, sizeof(login_info->drc_name));
 }
 
 /**

---
base-commit: ffc253263a1375a65fa6c9f62a893e9767fbebfa
change-id: 20231030-strncpy-drivers-scsi-ibmvscsi-ibmvfc-c-ccfce3255d58

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