Create a hook for inspecting program headers during library load

[Roland McGrath]

> 	* elf/dl-load.c (dl-load-phdr.h): Include.

The (...) is only for citing where you are touching.  There is no function,
variable, or macro called dl-load-phdr.h, so this is not right.  I'm also
not crazy about the name, since it sounds more generic than it really is.
dl-machine-reject-phdr.h would be the most specific name.

> 	(open_verify): Add hook for phdr check.

This should be more clear about what the change is.

> 	* sysdeps/generic/dl-load-phdr.h: New file.

The new file can go into elf/ instead of sysdeps/generic/, because it is
only used by code that is compiled only in the elf/ subdirectory.  The
sysdeps/generic/ directory is used for files that need to be found from
builds in multiple subdirectories.

If I'd written it, the whole log entry would look like:

	* elf/dl-machine-reject-phdr.h: New file.
	* elf/dl-load.c: #include that.
	(open_verify): Call elf_machine_reject_phdr_p and ignore the file
	if that returned false.

> +      if (__glibc_unlikely (
> +	     elf_machine_reject_phdr_p (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
> +					fd, loader)))

The indentation for this should look like:

      if (__glibc_unlikely (elf_machine_reject_phdr_p
			    (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
			     fd, loader)))

> +/* Machine-dependent ELF loader functions.

This description is too generic for what's really here.

> +#ifndef _DL_LOAD_PHDR_H
> +#define _DL_LOAD_PHDR_H

We always define these to 1 rather than empty.

You should #include <stdbool.h> here before using bool.

> +/* Return true iff ELF program headers are incompatible with the running
> +   host.  */
> +static inline bool
> +elf_machine_reject_phdr_p (const ElfW(Phdr) *phdr, uint_fast16_t phnum,
> +			   const char *buf, size_t len, int fd,
> +			   struct link_map *map)

It would be better to swap the order of the last two arguments, so you
don't have to integer types next to each other where transposing them
accidentally would not produce a type error.


Thanks,
Roland