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Message-ID: <202310182101.8C98652A5C@keescook> Date: Wed, 18 Oct 2023 21:32:50 -0700 From: Kees Cook <keescook@...omium.org> To: Alison Schofield <alison.schofield@...el.com> Cc: Justin Stitt <justinstitt@...gle.com>, Dan Williams <dan.j.williams@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, Ira Weiny <ira.weiny@...el.com>, nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] block: replace deprecated strncpy with strscpy On Wed, Oct 18, 2023 at 04:33:29PM -0700, Alison Schofield wrote: > On Wed, Oct 18, 2023 at 03:39:59PM -0700, Justin Stitt wrote: > > I have a feeling I may have botched the subject line for this patch. > > Can anyone confirm if it's good or not? > > > > Automated tooling told me that this was the most common patch > > prefix but it may be caused by large patch series that just > > happened to touch this file once. > > > > Should the subject be: nvdimm/btt: ... ? > > > > Judging from [1] I see a few "block" and a few of nvdimm/btt. > > Hi Justin, > > It should be nvdimm/btt because it only touches btt.c. > > Here's the old school way that I use to find prefixes. Maybe you can > train your automated tooling to do this, and then share it with me ;) > > I do: > > ~/git/linux/drivers/nvdimm$ git log --pretty=oneline --abbrev-commit btt.c > > 3222d8c2a7f8 block: remove ->rw_page > ba229aa8f249 nvdimm-btt: Use the enum req_op type > 86947df3a923 block: Change the type of the last .rw_page() argument > 8b9ab6266204 block: remove blk_cleanup_disk > 3205190655ea nvdimm-btt: use bvec_kmap_local in btt_rw_integrity > 322cbb50de71 block: remove genhd.h > > And I see a few choices, with 'block' being pretty common. > I peek in those patches and see that block was used when the patch > included files in drivers/block AND also in nvdimm/btt. Yeah, this "look into the patch" step is what was missing from the tool[1]. I've just tweaked it to weight based on number of files, and the results are more in line with what I'd expect now. The "top 5" best guesses are now: libnvdimm, btt: nvdimm/btt: nvdimm-btt: libnvdimm/btt: block: [1] https://github.com/kees/kernel-tools/blob/trunk/helpers/get-prefix > Use nvdimm/btt for your patch. > > A bit more below - > > > > > On Wed, Oct 18, 2023 at 3:35 PM Justin Stitt <justinstitt@...gle.com> 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. > > > > > > We expect super->signature to be NUL-terminated based on its usage with > > > memcpy against a NUL-term'd buffer: typo memcpy -> memcmp above? > > > btt_devs.c: > > > 253 | if (memcmp(super->signature, BTT_SIG, BTT_SIG_LEN) != 0) > > > btt.h: > > > 13 | #define BTT_SIG "BTT_ARENA_INFO\0" 1234567890123456 That's a funny way to define a string. :) Now it has two %NULs at the end. ;) It doesn't need that trailing '\0' #define BTT_SIG_LEN 16 And then this could be: #define BTT_SIG_LEN sizeof(BTT_SIG) But anyway... > > > > > > NUL-padding is not required as `super` is already zero-allocated: > > > btt.c: > > > 985 | super = kzalloc(sizeof(struct btt_sb), GFP_NOIO); > > > ... rendering any additional NUL-padding superfluous. > > > > > > 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. > > > > > > Let's also use the more idiomatic strscpy usage of (dest, src, > > > sizeof(dest)) instead of (dest, src, XYZ_LEN) for buffers that the > > > compiler can determine the size of. This more tightly correlates the > > > destination buffer to the amount of bytes copied. > > > > > > Side note, this pattern of memcmp() on two NUL-terminated strings should > > > really be changed to just a strncmp(), if i'm not mistaken? I see > > > multiple instances of this pattern in this system. > > I'm not following this note about memcmp() usage. Where is that? > > > > > > > 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\(" > > How you found it goes in the commit log, not below the line. > > > > --- > > > drivers/nvdimm/btt.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c > > > index d5593b0dc700..9372c36e8f76 100644 > > > --- a/drivers/nvdimm/btt.c > > > +++ b/drivers/nvdimm/btt.c > > > @@ -986,7 +986,7 @@ static int btt_arena_write_layout(struct arena_info *arena) > > > if (!super) > > > return -ENOMEM; > > > > > > - strncpy(super->signature, BTT_SIG, BTT_SIG_LEN); > > > + strscpy(super->signature, BTT_SIG, sizeof(super->signature)); Yup, this looks right to me. Reviewed-by: Kees Cook <keescook@...omium.org> -Kees -- Kees Cook
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