linux-hardening - [PATCH] dm ioctl: replace deprecated strncpy with strscpy

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Message-ID: <20230925-strncpy-drivers-md-dm-ioctl-c-v1-1-f0bfa093ef14@google.com>
Date: Mon, 25 Sep 2023 06:54:51 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] dm ioctl: replace deprecated strncpy with strscpy_pad

`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 `spec->target_type` to be NUL-terminated based on its use with
a format string after `dm_table_add_target()` is called
| 	r = dm_table_add_target(table, spec->target_type,
| 				(sector_t) spec->sector_start,
| 				(sector_t) spec->length,
| 				target_params);
... wherein `spec->target_type` is passed as parameter `type` and later
printed with DMERR:
|       DMERR("%s: %s: unknown target type", dm_device_name(t->md), type);

It appears that `spec` is not zero-allocated and thus NUL-padding may be
required in this ioctl context.

Considering the above, a suitable replacement is `strscpy_pad` due to
the fact that it guarantees NUL-termination whilst maintaining the
NUL-padding behavior that strncpy provides.

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>
---
Note: build-tested only.
---
 drivers/md/dm-ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 21ebb6c39394..e65058e0ed06 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1295,8 +1295,8 @@ static void retrieve_status(struct dm_table *table,
 		spec->status = 0;
 		spec->sector_start = ti->begin;
 		spec->length = ti->len;
-		strncpy(spec->target_type, ti->type->name,
-			sizeof(spec->target_type) - 1);
+		strscpy_pad(spec->target_type, ti->type->name,
+			sizeof(spec->target_type));

 		outptr += sizeof(struct dm_target_spec);
 		remaining = len - (outptr - outbuf);

---
base-commit: 6465e260f48790807eef06b583b38ca9789b6072
change-id: 20230925-strncpy-drivers-md-dm-ioctl-c-ea5c10e77981

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