On Thu, Jun 27, 2024 at 10:14:05AM -0700, Kees Cook wrote:
> On Wed, May 29, 2024 at 02:29:42PM -0700, Nathan Chancellor wrote:
> > Work for __counted_by on generic pointers in structures (not just
> > flexible array members) has started landing in Clang 19 (current tip of
> > tree). During the development of this feature, a restriction was added
> > to __counted_by to prevent the flexible array member's element type from
> > including a flexible array member itself such as:
> >
> > struct foo {
> > int count;
> > char buf[];
> > };
> >
> > struct bar {
> > int count;
> > struct foo data[] __counted_by(count);
> > };
> >
> > because the size of data cannot be calculated with the standard array
> > size formula:
> >
> > sizeof(struct foo) * count
> >
> > This restriction was downgraded to a warning but due to CONFIG_WERROR,
> > it can still break the build. The application of __counted_by on the
> > ports member of 'struct mxser_board' triggers this restriction,
> > resulting in:
> >
> > drivers/tty/mxser.c:291:2: error: 'counted_by' should not be applied to an array with element of unknown size because 'struct mxser_port' is a struct type with a flexible array member. This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size]
> > 291 | struct mxser_port ports[] __counted_by(nports);
> > | ^~~~~~~~~~~~~~~~~~~~~~~~~
> > 1 error generated.
> >
> > Remove this use of __counted_by to fix the warning/error. However,
> > rather than remove it altogether, leave it commented, as it may be
> > possible to support this in future compiler releases.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Closes: https://github.com/ClangBuiltLinux/linux/issues/2026
> > Fixes: f34907ecca71 ("mxser: Annotate struct mxser_board with __counted_by")
> > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
>
> Since this fixes a build issue under Clang, can we please land this so
> v6.7 and later will build again? Gustavo is still working on the more
> complete fix (which was already on his radar, so it won't be lost).
>
> If it's easier/helpful, I can land this via the hardening tree? I was
> the one who sent the bad patch originally. :)
>
I don't see this in my queue anywhere, sorry, can you resend it? Or
feel free to take it through your trees, no objection from me there.
thanks,
greg k-h
