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Message-ID: <202310191619.6BE8E38@keescook> Date: Thu, 19 Oct 2023 16:20:28 -0700 From: Kees Cook <keescook@...omium.org> To: Justin Stitt <justinstitt@...gle.com> Cc: James Smart <james.smart@...adcom.com>, Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] nvme-fc: replace deprecated strncpy with strscpy On Thu, Oct 19, 2023 at 09:34:35PM +0000, Justin Stitt wrote: > strncpy() is deprecated for use on NUL-terminated destination strings > [1] and as such we should prefer more robust and less ambiguous string > interfaces. > > Let's instead use strscpy() [2] as it guarantees NUL-termination on the > destination buffer. > > Moreover, there is no need to use: > > | min(FCNVME_ASSOC_HOSTNQN_LEN, NVMF_NQN_SIZE)); > > I imagine this was originally done to make sure the destination buffer > is NUL-terminated by ensuring we copy a number of bytes less than the > size of our destination, thus leaving some NUL-bytes at the end. Yeah, this is odd, but I agree that the resulting strscpy does the intended copy, since we've seen that other nqn strings are expected to be %NUL terminated. > > However, with strscpy(), we no longer need to do this and we can instead > opt for the more idiomatic strscpy() usage of: > > | strscpy(dest, src, sizeof(dest)) > > Also, no NUL-padding is required as lsop is zero-allocated: > > | lsop = kzalloc((sizeof(*lsop) + > | sizeof(*assoc_rqst) + sizeof(*assoc_acc) + > | ctrl->lport->ops->lsrqst_priv_sz), GFP_KERNEL); > > ... and assoc_rqst points to a field in lsop: > > | assoc_rqst = (struct fcnvme_ls_cr_assoc_rqst *)&lsop[1]; > > Therefore, any additional NUL-byte assignments (like the ones that > strncpy() makes) are redundant. > > 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> > Similar-to: https://lore.kernel.org/all/20231018-strncpy-drivers-nvme-host-fabrics-c-v1-1-b6677df40a35@google.com/ Reviewed-by: Kees Cook <keescook@...omium.org> -- Kees Cook
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