On Wed, Aug 28, 2024 at 05:09:08PM +0200, Alejandro Colomar wrote: > Hi Kees, > > On Wed, Aug 28, 2024 at 06:48:39AM GMT, Kees Cook wrote: > > [...] > > > >Thank you for your suggestion. How does the following commit log look > > >to you? Does it meet your expectations? > > > > > > string: Use ARRAY_SIZE() in strscpy() > > > > > > We can use ARRAY_SIZE() instead to clarify that they are regular characters. > > > > > > Co-developed-by: Alejandro Colomar <alx@xxxxxxxxxx> > > > Signed-off-by: Alejandro Colomar <alx@xxxxxxxxxx> > > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> > > > > > >diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h > > >index bbab79c0c074..07216996e3a9 100644 > > >--- a/arch/um/include/shared/user.h > > >+++ b/arch/um/include/shared/user.h > > >@@ -14,7 +14,7 @@ > > > * copying too much infrastructure for my taste, so userspace files > > > * get less checking than kernel files. > > > */ > > >-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) > > >+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x)) > > > > > > /* This is to get size_t and NULL */ > > > #ifndef __UM_HOST__ > > >@@ -60,7 +60,7 @@ static inline void print_hex_dump(const char *level, > > >const char *prefix_str, > > > extern int in_aton(char *str); > > > extern size_t strlcat(char *, const char *, size_t); > > > extern size_t sized_strscpy(char *, const char *, size_t); > > >-#define strscpy(dst, src) sized_strscpy(dst, src, sizeof(dst)) > > >+#define strscpy(dst, src) sized_strscpy(dst, src, ARRAY_SIZE(dst)) > > > > Uh, but why? strscpy() copies bytes, not array elements. Using sizeof() is already correct and using ARRAY_SIZE() could lead to unexpectedly small counts (in admittedly odd situations). > > > > What is the problem you're trying to solve here? > > I suggested that here: > <https://lore.kernel.org/all/2jxak5v6dfxlpbxhpm3ey7oup4g2lnr3ueurfbosf5wdo65dk4@srb3hsk72zwq/> > > There, you'll find the rationale (and also for avoiding the _pad calls > where not necessary --I ignore if it's necessary here--). Right, so we only use byte strings for strscpy(), so sizeof() is sufficient. There's no technical need to switch to ARRAY_SIZE(), and I'd like to minimize any changes to such core APIs without a good reason. And for the _pad change, we are also doing strncpy() replacement via case-by-case analysis, but with a common function like get_task_comm(), I don't want to change the behavior without a complete audit of the padding needs of every caller. Since that's rather a lot for this series, I'd rather we just leave the existing behavior as-is, and if padding removal is wanted after that, we can do it on a case-by-case basis then. -Kees -- Kees Cook
