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Message-ID: <20231019-strncpy-drivers-nvdimm-btt-c-v2-1-366993878cf0@google.com> Date: Thu, 19 Oct 2023 17:54:15 +0000 From: Justin Stitt <justinstitt@...gle.com> To: 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> Cc: nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>, Kees Cook <keescook@...omium.org> Subject: [PATCH v2] nvdimm/btt: replace deprecated strncpy with strscpy Found with grep. 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 memcmp against a NUL-term'd buffer: btt_devs.c: 253 | if (memcmp(super->signature, BTT_SIG, BTT_SIG_LEN) != 0) btt.h: 13 | #define BTT_SIG "BTT_ARENA_INFO\0" 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: | if (memcmp(super->signature, BTT_SIG, BTT_SIG_LEN) != 0) | return false; where BIT_SIG is defined (weirdly) as a double NUL-terminated string: | #define BTT_SIG "BTT_ARENA_INFO\0" 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> Reviewed-by: Kees Cook <keescook@...omium.org> --- Changes in v2: - provide more details about memcmp() - fix typos in commit msg (thanks Kees) - fix subject line (thanks Alison) - Link to v1: https://lore.kernel.org/r/20231018-strncpy-drivers-nvdimm-btt-c-v1-1-58070f7dc5c9@google.com --- Note: build-tested only. --- 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)); export_uuid(super->uuid, nd_btt->uuid); export_uuid(super->parent_uuid, parent_uuid); super->flags = cpu_to_le32(arena->flags); --- base-commit: 58720809f52779dc0f08e53e54b014209d13eebb change-id: 20231018-strncpy-drivers-nvdimm-btt-c-15f93879989e Best regards, -- Justin Stitt <justinstitt@...gle.com>
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