On Wed, Sep 06, 2023 at 04:09:01PM +0200, Ingo Molnar wrote: > > * Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > > > Hi Ingo, > > > > On 9/6/23 14:10, Ingo Molnar wrote: > > > > > > * Justin Stitt <justinstitt@xxxxxxxxxx> wrote: > > > > > >> Both `strncpy` and `strcpy` are deprecated for use on NUL-terminated > > >> destination strings [1]. > > >> > > >> We can see that `arg` and `uv_nmi_action` are expected to be > > >> NUL-terminated strings due to their use within `strcmp()` and format > > >> strings respectively. > > >> > > >> With this in mind, a suitable replacement is `strscpy` [2] due to the > > >> fact that it guarantees NUL-termination on its destination buffer > > >> argument which is _not_ the case for `strncpy` or `strcpy`! > > >> > > >> In this case, we can drop both the forced NUL-termination and the `... -1` from: > > >> | strncpy(arg, val, ACTION_LEN - 1); > > >> as `strscpy` implicitly has this behavior. > > >> > > >> Link: 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@xxxxxxxxxxxxxxx > > >> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx> > > > > > >> arch/x86/platform/uv/uv_nmi.c | 7 +++---- > > >> 1 file changed, 3 insertions(+), 4 deletions(-) > > > > > > Note that this commit is already upstream: > > > > > > 1e6f01f72855 ("x86/platform/uv: Refactor code using deprecated strcpy()/strncpy() interfaces to use strscpy()") > > > > > > Below is the delta your v3 patch has compared to what is upstream - is it > > > really necessary to open code it, instead of using strnchrnul() as your > > > original patch did? Am I missing anything here? > > > > The new version is a result of a review from my because IMHO: > > > > strscpy(arg, val, strnchrnul(val, sizeof(arg)-1, '\n') - val + 1); > > > > Is really unreadable / really hard to reason about if > > this is actually correct and does not contain any > > of by 1 bugs. > > > > Note that the diff of v3 compared to the code before v2 landed is > > actually smaller now and actually matches the subject of: > > "refactor deprecated strcpy and strncpy" > > > > Where as v2 actually touches more code / refactor things > > which fall outside of a "one change per patch" approach. > > The: > > > > p = strchr(arg, '\n'); > > if (p) > > *p = '\0'; > > > > was already there before v2 landed. > > > > I also suggested to do a follow up patch to change things to: > > > > strscpy(arg, val, sizeof(arg)); > > p = strchrnul(arg, '\n'); > > *p = '\0'; > > > > Which IMHO is much more readable then what has landed > > now. But since v2 has already landed I guess the best > > thing is just to stick with what we have upstream now... > > Well, how about we do a delta patch with all the changes > you suggested? I'm all for readability. For whatever it's worth, I vote in favor of adopting an increased readability version. I was on vacation when the patch came through, and by the time I reviewed it it was already accepted. I still puzzled through the -1/+1 stuff to be sure it functioned correctly; since it worked and was already accepted, I let it go. When Hans' comments on readability later came through, I was thinking "Yes, he's exactly right! Why, when I worked so hard on verifying that the code worked properly, did it not occur to me to suggest re-writing this in a simpler fashion to make the intent clear?" Thanks, --> Steve Wahl -- Steve Wahl, Hewlett Packard Enterprise
