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

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Message-ID: <20230925-strncpy-drivers-md-dm-log-userspace-base-c-v1-1-030d7bcf1004@google.com>
Date: Mon, 25 Sep 2023 07:06:03 +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, 
	Kees Cook <keescook@...omium.org>, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] dm log userspace: 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.

`lc` is already zero-allocated:
|       lc = kzalloc(sizeof(*lc), GFP_KERNEL);
... as such, any future NUL-padding is superfluous.

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

Let's also go with the more idiomatic `dest, src, sizeof(dest)` pattern
for destination buffers that the compiler can calculate the size for.

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
Cc: Kees Cook <keescook@...omium.org>
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.
---
 drivers/md/dm-log-userspace-base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
index 5aace6ee6d47..7e4f27e86150 100644
--- a/drivers/md/dm-log-userspace-base.c
+++ b/drivers/md/dm-log-userspace-base.c
@@ -224,7 +224,7 @@ static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
 
 	lc->usr_argc = argc;
 
-	strncpy(lc->uuid, argv[0], DM_UUID_LEN);
+	strscpy(lc->uuid, argv[0], sizeof(lc->uuid));
 	argc--;
 	argv++;
 	spin_lock_init(&lc->flush_lock);

---
base-commit: 6465e260f48790807eef06b583b38ca9789b6072
change-id: 20230925-strncpy-drivers-md-dm-log-userspace-base-c-857579d9834f

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