Re: [PATCH 0/2] libc: Fix __dl_iterate_phdr to work from auditcontext

[Jiri Olsa <jolsa at redhat dot com>]

hi,
any feedback on this? I created related BZ as well (unwind-wise related)
http://sourceware.org/bugzilla/show_bug.cgi?id=13113

anything else I can do to get any info?

thanks,
jirka

On Mon, Aug 08, 2011 at 02:37:00PM +0200, Jiri Olsa wrote:
> hi,
> any feedback on this?
> 
> thanks,
> jirka
> 
> On Tue, Jul 26, 2011 at 12:34:52PM +0200, Jiri Olsa wrote:
> > hi,
> > 
> > if __dl_iterate_phdr is called from audit context, it will not
> > provide all the info the callback. Some of the fields are just
> > zero. The test audit library source is attached.
> > 
> > The reason is, that inside the audit namespace the dynamic loader
> > link_map object is just a mirror of the real one. And it does not
> > have all the info filled in.
> > 
> > I prepared 2 fixies for this, since I'm not sure which way
> > you'll like more.. maybe neither ;)
> > 
> > attached patches:
> >  1/2 - "libc: Fix _dl_map_object_from_fd to update ld.so link_map mirror object"
> >        filling in needed values for dynamic loader mirror link_map object
> >  2/2 - "libc: Fix __dl_iterate_phdr to take values from real link_map object"
> >        using l_real link_map to get the values for __dl_iterate_phdr callback
> > 
> > 
> > The justification for this change is that libunwind is using
> > __dl_iterate_phdr to locate all the unwind info. So with current
> > behaviour, the stack that unwinds from audit context will stop at
> > the dynamic loader and does not continue through the application
> > itself. It works properly with either of above fixies.
> > 
> > 
> > thanks,
> > jirka
> > ---
> > #include <link.h>
> > #include <dlfcn.h>
> > #include <stdio.h>
> > #include <sys/time.h>
> > #include <execinfo.h>
> > #include <link.h>
> > 
> > static int callback(struct dl_phdr_info *info, size_t size, void *data)
> > {
> > 	printf("AUDIT got %s, base=0x%lx, dlpi_phnum %d\n",
> > 		info->dlpi_name,
> > 		(long) info->dlpi_addr,
> > 		info->dlpi_phnum);
> > 	return 0;
> > 
> > }
> > 
> > unsigned int la_version (unsigned int v)
> > {
> > 	return v;
> > }
> > 
> > unsigned int la_objopen(struct link_map *l, Lmid_t a, uintptr_t *cookie)
> > {
> > 	return 3;
> > }
> > 
> > uintptr_t la_symbind32(Elf32_Sym *sym, unsigned int ndx, uintptr_t *refcook,
> >           uintptr_t *defcook, unsigned int *flags, const char *symname)
> > {
> > 	*flags = 0;
> > 	return sym->st_value;
> > }
> > 
> > uintptr_t la_symbind64(Elf64_Sym *sym, unsigned int ndx, uintptr_t *refcook,
> >                 uintptr_t *defcook, unsigned int *flags, const char *symname)
> > {
> > 	*flags = 0;
> > 	return sym->st_value;
> > }
> > 
> > Elf64_Addr la_x86_64_gnu_pltenter (Elf64_Sym *__sym,
> >                                           unsigned int __ndx,
> >                                           uintptr_t *__refcook,
> >                                           uintptr_t *__defcook,
> >                                           La_x86_64_regs *__regs,
> >                                           unsigned int *__flags,
> >                                           const char *__symname,
> >                                           long int *__framesizep)
> > {
> > 	printf("entry %s\n", __symname);
> > 	*__framesizep = 100;
> > 	dl_iterate_phdr(callback, NULL);
> > 	return __sym->st_value;
> > }
> > 
> > unsigned int la_x86_64_gnu_pltexit (Elf64_Sym *__sym,
> >                                            unsigned int __ndx,
> >                                            uintptr_t *__refcook,
> >                                            uintptr_t *__defcook,
> >                                            const La_x86_64_regs *__inregs,
> >                                            La_x86_64_retval *__outregs,
> >                                            const char *__symname)
> > {
> > 	return 0;
> > }
> > 
> > void la_activity(uintptr_t *cookie, unsigned int act)
> > {
> > }
> > 
> > char* la_objsearch(const char *name, uintptr_t *cookie, unsigned int flag)
> > {
> > 	return (char*) name;
> > }
> > 
> > void la_preinit(uintptr_t *__cookie)
> > {
> > }
> > 
> > unsigned int la_objclose(uintptr_t *__cookie)
> > {
> > 	return 0;
> > }