Re: [PATCH] build-id: require program headers to be right after ELF header

[Alexey Dobriyan]

On Fri, Jun 21, 2024 at 10:07:52AM -0700, Andrew Morton wrote:
> On Fri, 21 Jun 2024 18:05:50 +0300 Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote:
> 
> > ELF spec doesn't require program header to be placed right after
> > ELF header, but build-id code very much assumes such placement:
> > 
> > 	find_get_page(vma->vm_file->f_mapping, 0);
> > 
> > and later check against PAGE_SIZE.
> > 
> > Returns errors for now until someone rewrites build-id parser
> > to be more correct.
> >
> > ...
> >
> > --- a/lib/buildid.c
> > +++ b/lib/buildid.c
> > @@ -73,6 +73,9 @@ static int get_build_id_32(const void *page_addr, unsigned char *build_id,
> >  	Elf32_Phdr *phdr;
> >  	int i;
> >  
> > +	if (ehdr->e_phoff != sizeof(Elf32_Ehdr)) {
> > +		return -EINVAL;
> > +	}
> >  	/* only supports phdr that fits in one page */
> >  	if (ehdr->e_phnum >
> >  	    (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
> > @@ -98,6 +101,9 @@ static int get_build_id_64(const void *page_addr, unsigned char *build_id,
> >  	Elf64_Phdr *phdr;
> >  	int i;
> >  
> > +	if (ehdr->e_phoff != sizeof(Elf64_Ehdr)) {
> > +		return -EINVAL;
> > +	}
> >  	/* only supports phdr that fits in one page */
> >  	if (ehdr->e_phnum >
> >  	    (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
> 
> Well can we get comments in here eplaining the shortcoming?  That way
> we're more likely to get a volunteer.

Sure.

> And please drop the braces?

Bracers are good. It took hundred years to drop -Wdeclaration-after-statement,
I hope to see mandatory bracers by 2050.