linux-hardening - [PATCH] pstore/blk: replace deprecated strncpy with strscpy

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Message-ID: <20240328-strncpy-fs-pstore-blk-c-v1-1-5748cdc22a53@google.com>
Date: Thu, 28 Mar 2024 20:54:16 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Kees Cook <keescook@...omium.org>, Tony Luck <tony.luck@...el.com>, 
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] pstore/blk: 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 know that info-device should be NUL-terminated based on its use with
strlen():
|	static int __init mtdpstore_init(void)
|	{
|		int ret;
|		struct mtdpstore_context *cxt = &oops_cxt;
|		struct pstore_blk_config *info = &cxt->info;
|
|		ret = pstore_blk_get_config(info);
|		if (unlikely(ret))
|			return ret;
|
|		if (strlen(info->device) == 0) {
|			pr_err("mtd device must be supplied (device name is empty)\n");
...

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer.

Note that this patch relies on the _new_ 2-argument version of strscpy()
introduced in Commit e6584c3964f2f ("string: Allow 2-argument strscpy()").

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\("
---
 fs/pstore/blk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pstore/blk.c b/fs/pstore/blk.c
index de8cf5d75f34..65b2473e22ff 100644
--- a/fs/pstore/blk.c
+++ b/fs/pstore/blk.c
@@ -241,7 +241,7 @@ static int __register_pstore_blk(struct pstore_device_info *dev,
 /* get information of pstore/blk */
 int pstore_blk_get_config(struct pstore_blk_config *info)
 {
-	strncpy(info->device, blkdev, 80);
+	strscpy(info->device, blkdev);
 	info->max_reason = max_reason;
 	info->kmsg_size = check_size(kmsg_size, 4096);
 	info->pmsg_size = check_size(pmsg_size, 4096);

---
base-commit: 928a87efa42302a23bb9554be081a28058495f22
change-id: 20240328-strncpy-fs-pstore-blk-c-8c1c0c3079f3

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