misc/84199: dlinfo in libexec/elf-rtld/rtld.c does not handle RTLD_DI_SERINFOSIZE properly

[William Josephson]

>Number:         84199
>Category:       misc
>Synopsis:       dlinfo in libexec/elf-rtld/rtld.c does not handle RTLD_DI_SERINFOSIZE properly
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Jul 28 00:20:19 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     William Josephson
>Release:        
>Organization:
>Environment:
FreeBSD 4.x and 5.4, presumably 6 and -CURRENT, too.
>Description:
I've run across a bug in the ELF dynamic linker in FreeBSD 4.x
and FreeBSD 5.4.  Although I haven't had a chance to compile or
install FreeBSD 6 yet, the bug appears to be in the ELF dynamic
linker in at least FreeBSD 4 through -CURRENT.  The problem is
that do_search_info in libexec/rtld-elf/rtld.c does not account
for the space required by Dl_serpath structures with either the
RTLD_DI_SERINFOSIZE, or the RTLD_DI_SERINFO requests.  The
example program in the dlinfo man page happens to work, but a
simple loop copying the path strings into a buffer allocated with
malloc will corrupt the heap.  The program below illustrates the
problem.  Given that the arithmetic in do_search_info is easily
fixed, it might be worth patching before the upcoming release.

	#include <link.h>
	#include <dlfcn.h>
	#include <stdio.h>
	#include <stdlib.h>
	
	int
	main(int argc, char *argv[])
	{
		char *s;
		Dl_serinfo *p;
		Dl_serinfo info;
	
		memset(&info, 0, sizeof(info));
		dlinfo(RTLD_SELF, RTLD_DI_SERINFOSIZE, (void*)&info);
		p = malloc(info.dls_size);
		memset(p, 0, info.dls_size);
		p->dls_cnt = info.dls_cnt;
		p->dls_size = info.dls_size;
		dlinfo(RTLD_SELF, RTLD_DI_SERINFO, (void*)p);
		s = p->dls_serpath[p->dls_cnt-1].dls_name;
		s += strlen(s)+1;
		printf("%d %d %d %d %d\n", info.dls_size, (char*)s-(char*)p,
			((char*)s-(char*)p)-info.dls_size, sizeof(Dl_serpath),
			info.dls_cnt*sizeof(Dl_serpath));
		return 0;
	}

>How-To-Repeat:
Run the above program.
>Fix:
Fix arithmetic in do_search_info as described above.
>Release-Note:
>Audit-Trail:
>Unformatted: