linux-hardening - [PATCH] nvme-fabrics: replace deprecated strncpy with strscpy

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Message-ID: <20231018-strncpy-drivers-nvme-host-fabrics-c-v1-1-b6677df40a35@google.com>
Date: Wed, 18 Oct 2023 22:48:49 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>, 
	Sagi Grimberg <sagi@...mberg.me>
Cc: linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] nvme-fabrics: 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 both data->subsysnqn and data->hostnqn to be NUL-terminated
based on their usage with format specifier ("%s"):
fabrics.c:
322: dev_err(ctrl->device,
323:   "%s, subsysnqn \"%s\"\n",
324:   inv_data, data->subsysnqn);
...
349: dev_err(ctrl->device,
350: 	 "Connect for subsystem %s is not allowed, hostnqn: %s\n",
351: 	 data->subsysnqn, data->hostnqn);

Moreover, there's no need to NUL-pad since `data` is zero-allocated
already in fabrics.c:
383: data = kzalloc(sizeof(*data), GFP_KERNEL);
... therefore any further NUL-padding is rendered useless.

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.

I opted not to switch NVMF_NQN_SIZE to sizeof(data->xyz) because the
size is defined as:
|       /* NQN names in commands fields specified one size */
|       #define NVMF_NQN_FIELD_LEN	256

... while NVMF_NQN_SIZE is defined as:
|       /* However the max length of a qualified name is another size */
|       #define NVMF_NQN_SIZE		223

Since 223 seems pretty magic, I'm not going to touch it.

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/nvme/host/fabrics.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index 8175d49f2909..57aad3ce311a 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -386,8 +386,8 @@ static struct nvmf_connect_data *nvmf_connect_data_prep(struct nvme_ctrl *ctrl,

 	uuid_copy(&data->hostid, &ctrl->opts->host->id);
 	data->cntlid = cpu_to_le16(cntlid);
-	strncpy(data->subsysnqn, ctrl->opts->subsysnqn, NVMF_NQN_SIZE);
-	strncpy(data->hostnqn, ctrl->opts->host->nqn, NVMF_NQN_SIZE);
+	strscpy(data->subsysnqn, ctrl->opts->subsysnqn, NVMF_NQN_SIZE);
+	strscpy(data->hostnqn, ctrl->opts->host->nqn, NVMF_NQN_SIZE);

 	return data;
 }

---
base-commit: 58720809f52779dc0f08e53e54b014209d13eebb
change-id: 20231018-strncpy-drivers-nvme-host-fabrics-c-416258a22598

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