Re: libltdl is inefficient and a security hazard

[Bob Friesenhahn]

Doing some investigation under Linux, I see that libltdl does the same 
wrong things under Linux except that Linux employs some algorithms 
which makes doing the wrong things much less expensive than under 
Solaris.  Linux prunes directories in the search path which were found 
to not exist from later searches.  Linux also entirely ignores 
requests to load libraries which were already loaded.  However, Linux 
does still try to dlopen() a ".a" archive file.

Here is a strace done under Linux showing only the system calls which 
pass file names (strace -e trace=file command).  The modules loaded 
were "null.la" and "xc.la":

execve("/usr/local/bin/gm", ["gm", "convert", "-size", "1x1", "xc:white", 
"null:"], [/* 50 vars */]) = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/local/lib/libGraphicsMagick.so.3", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/liblcms.so.1", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libfreetype.so.6", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libXext.so.6", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libSM.so.6", O_RDONLY)   = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libICE.so.6", O_RDONLY)  = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libX11.so.6", O_RDONLY)  = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/libbz2.so.1.0", O_RDONLY)    = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libz.so.1", O_RDONLY)    = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/libm.so.6", O_RDONLY)        = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libgomp.so.1", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/libpthread.so.0", O_RDONLY)  = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/libdl.so.2", O_RDONLY)       = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/libc.so.6", O_RDONLY)        = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libXau.so.6", O_RDONLY)  = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libxcb-xlib.so.0", O_RDONLY) = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libxcb.so.1", O_RDONLY)  = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/librt.so.1", O_RDONLY)       = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/usr/lib/libXdmcp.so.6", O_RDONLY) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
open("/proc/meminfo", O_RDONLY)         = 3
open("/proc/stat", O_RDONLY)            = 3
open("/usr/lib/gconv/gconv-modules.cache", O_RDONLY) = 3
open("/usr/local/share/GraphicsMagick-1.4/config/modules.mgk", O_RDONLY) = 3
getcwd("/"..., 2052)                    = 2
access("/usr/local/lib/GraphicsMagick-1.4/modules-Q16/coders/null.la", R_OK) = 0
open("/usr/local/lib/GraphicsMagick-1.4/modules-Q16/coders/null.la", O_RDONLY) 
= 3
open("/etc/ld.so.cache", O_RDONLY)      = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/tls/x86_64/null.a", O_RDONLY) = -1 ENOENT (No such file or directory)
stat("/lib/tls/x86_64", 0x7fffbac4e380) = -1 ENOENT (No such file or directory)
open("/lib/tls/null.a", O_RDONLY)       = -1 ENOENT (No such file or directory)
stat("/lib/tls", 0x7fffbac4e380)        = -1 ENOENT (No such file or directory)
open("/lib/x86_64/null.a", O_RDONLY)    = -1 ENOENT (No such file or directory)
stat("/lib/x86_64", 0x7fffbac4e380)     = -1 ENOENT (No such file or directory)
open("/lib/null.a", O_RDONLY)           = -1 ENOENT (No such file or directory)
stat("/lib", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/usr/lib/tls/x86_64/null.a", O_RDONLY) = -1 ENOENT (No such file or 
directory)
stat("/usr/lib/tls/x86_64", 0x7fffbac4e380) = -1 ENOENT (No such file or 
directory)
open("/usr/lib/tls/null.a", O_RDONLY)   = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls", 0x7fffbac4e380)    = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64/null.a", O_RDONLY) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7fffbac4e380) = -1 ENOENT (No such file or directory)
open("/usr/lib/null.a", O_RDONLY)       = -1 ENOENT (No such file or directory)
stat("/usr/lib", {st_mode=S_IFDIR|0755, st_size=135168, ...}) = 0
open("/lib/x86_64-linux-gnu/tls/x86_64/null.a", O_RDONLY) = -1 ENOENT (No such 
file or directory)
stat("/lib/x86_64-linux-gnu/tls/x86_64", 0x7fffbac4e380) = -1 ENOENT (No such 
file or directory)
open("/lib/x86_64-linux-gnu/tls/null.a", O_RDONLY) = -1 ENOENT (No such file or 
directory)
stat("/lib/x86_64-linux-gnu/tls", 0x7fffbac4e380) = -1 ENOENT (No such file or 
directory)
open("/lib/x86_64-linux-gnu/x86_64/null.a", O_RDONLY) = -1 ENOENT (No such file 
or directory)
stat("/lib/x86_64-linux-gnu/x86_64", 0x7fffbac4e380) = -1 ENOENT (No such file 
or directory)
open("/lib/x86_64-linux-gnu/null.a", O_RDONLY) = -1 ENOENT (No such file or 
directory)
stat("/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/usr/lib/x86_64-linux-gnu/tls/x86_64/null.a", O_RDONLY) = -1 ENOENT (No 
such file or directory)
stat("/usr/lib/x86_64-linux-gnu/tls/x86_64", 0x7fffbac4e380) = -1 ENOENT (No 
such file or directory)
open("/usr/lib/x86_64-linux-gnu/tls/null.a", O_RDONLY) = -1 ENOENT (No such 
file or directory)
stat("/usr/lib/x86_64-linux-gnu/tls", 0x7fffbac4e380) = -1 ENOENT (No such file 
or directory)
open("/usr/lib/x86_64-linux-gnu/x86_64/null.a", O_RDONLY) = -1 ENOENT (No such 
file or directory)
stat("/usr/lib/x86_64-linux-gnu/x86_64", 0x7fffbac4e380) = -1 ENOENT (No such 
file or directory)
open("/usr/lib/x86_64-linux-gnu/null.a", O_RDONLY) = -1 ENOENT (No such file or 
directory)
stat("/usr/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/usr/share/locale/locale.alias", O_RDONLY) = 3
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT 
(No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT 
(No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No 
such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT 
(No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No 
such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such 
file or directory)
open("/usr/local/lib/GraphicsMagick-1.4/modules-Q16/coders/null.so", O_RDONLY) 
= 3
access("/usr/local/lib/GraphicsMagick-1.4/modules-Q16/coders/xc.la", R_OK) = 0
open("/usr/local/lib/GraphicsMagick-1.4/modules-Q16/coders/xc.la", O_RDONLY) = 3
open("/etc/ld.so.cache", O_RDONLY)      = 3
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/xc.a", O_RDONLY)             = -1 ENOENT (No such file or directory)
open("/usr/lib/xc.a", O_RDONLY)         = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/xc.a", O_RDONLY) = -1 ENOENT (No such file or 
directory)
open("/usr/lib/x86_64-linux-gnu/xc.a", O_RDONLY) = -1 ENOENT (No such file or 
directory)
open("/usr/local/lib/GraphicsMagick-1.4/modules-Q16/coders/xc.so", O_RDONLY) = 3
open("/usr/local/share/GraphicsMagick-1.4/config/colors.mgk", O_RDONLY) = 3

Bob
--
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/