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Message-ID: <202309301342.5B5BED40A1@keescook> Date: Sat, 30 Sep 2023 13:57:09 -0700 From: Kees Cook <keescook@...omium.org> To: Christophe JAILLET <christophe.jaillet@...adoo.fr> Cc: Ian Abbott <abbotti@....co.uk>, H Hartley Sweeten <hsweeten@...ionengravers.com>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org, linux-hardening@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [PATCH] comedi: Annotate struct comedi_lrange with __counted_by On Sat, Sep 30, 2023 at 11:14:47AM +0200, Christophe JAILLET wrote: > Prepare for the coming implementation by GCC and Clang of the __counted_by > attribute. Flexible array members annotated with __counted_by can have > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family > functions). > > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr> > --- > This patch is part of a work done in parallel of what is currently worked > on by Kees Cook. > > My patches are only related to corner cases that do NOT match the > semantic of his Coccinelle script[1]. Nice! struct comedi_lrange { int length; struct comedi_krange range[]; }; ... static const struct comedi_lrange range_rti800_ai_10_bipolar = { 4, { BIP_RANGE(10), BIP_RANGE(1), BIP_RANGE(0.1), BIP_RANGE(0.02) } }; I'm struggling to come up with a way for Coccinelle to find this kind of thing in other places... > In this case, it is been spotted because of comedi_alloc_spriv(). > All other usages of struct comedi_lrange seem to be static definition of > the structure that explicitly set the .length field. Ah-ha, I found it in drivers/comedi/drivers/das16.c das16_ai_range(): lrange = comedi_alloc_spriv(s, struct_size(lrange, range, 1)); I was also able to find this: union jr3_pci_single_range { struct comedi_lrange l; char _reserved[offsetof(struct comedi_lrange, range[1])]; }; Which looks a lot like DEFINE_FLEX: https://lore.kernel.org/linux-hardening/20230912115937.1645707-2-przemyslaw.kitszel@intel.com/ But that above for stack varaibles rather than globals. But I'm way off topic now. ;) Reviewed-by: Kees Cook <keescook@...omium.org> > > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci > --- > include/linux/comedi/comedidev.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/comedi/comedidev.h b/include/linux/comedi/comedidev.h > index 0a1150900ef3..c08416a7364b 100644 > --- a/include/linux/comedi/comedidev.h > +++ b/include/linux/comedi/comedidev.h > @@ -633,7 +633,7 @@ extern const struct comedi_lrange range_unknown; > */ > struct comedi_lrange { > int length; > - struct comedi_krange range[]; > + struct comedi_krange range[] __counted_by(length); > }; > > /** > -- > 2.34.1 > -- Kees Cook
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