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#!/usr/bin/python3
# Copyright 2013 Jussi Pakkanen
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import sys, struct
SHT_STRTAB = 3
DT_NEEDED = 1
DT_RPATH = 15
DT_STRTAB = 5
DT_SONAME = 14
def init_datasizes(self, ptrsize):
self.Half = 'h'
self.HalfSize = 2
self.Word = 'I'
self.WordSize = 4
self.Sword = 'i'
self.SwordSize = 4
if ptrsize == 64:
self.Addr = 'Q'
self.AddrSize = 8
self.Off = 'Q'
self.OffSize = 8
self.XWord = 'Q'
self.XWordSize = 8
self.Sxword = 'q'
self.SxwordSize = 8
else:
self.Addr = 'I'
self.AddrSize = 4
self.Off = 'I'
self.OffSize = 4
class DynamicEntry():
def __init__(self, ifile, ptrsize):
init_datasizes(self, ptrsize)
if ptrsize == 64:
self.d_tag = struct.unpack(self.Sxword, ifile.read(self.SxwordSize))[0];
self.val = struct.unpack(self.XWord, ifile.read(self.XWordSize))[0];
else:
self.d_tag = struct.unpack(self.Sword, ifile.read(self.SwordSize))[0]
self.val = struct.unpack(self.Word, ifile.read(self.WordSize))[0]
class SectionHeader():
def __init__(self, ifile, ptrsize):
init_datasizes(self, ptrsize)
if ptrsize == 64:
is_64 = True
else:
is_64 = False
#Elf64_Word
self.sh_name = struct.unpack(self.Word, ifile.read(self.WordSize))[0];
#Elf64_Word
self.sh_type = struct.unpack(self.Word, ifile.read(self.WordSize))[0]
#Elf64_Xword
if is_64:
self.sh_flags = struct.unpack(self.XWord, ifile.read(self.XWordSize))[0]
else:
self.sh_flags = struct.unpack(self.Word, ifile.read(self.WordSize))[0]
#Elf64_Addr
self.sh_addr = struct.unpack(self.Addr, ifile.read(self.AddrSize))[0];
#Elf64_Off
self.sh_offset = struct.unpack(self.Off, ifile.read(self.OffSize))[0]
#Elf64_Xword
if is_64:
self.sh_size = struct.unpack(self.XWord, ifile.read(self.XWordSize))[0]
else:
self.sh_size = struct.unpack(self.Word, ifile.read(self.WordSize))[0]
#Elf64_Word
self.sh_link = struct.unpack(self.Word, ifile.read(self.WordSize))[0];
#Elf64_Word
self.sh_info = struct.unpack(self.Word, ifile.read(self.WordSize))[0];
#Elf64_Xword
if is_64:
self.sh_addralign = struct.unpack(self.XWord, ifile.read(self.XWordSize))[0]
else:
self.sh_addralign = struct.unpack(self.Word, ifile.read(self.WordSize))[0]
#Elf64_Xword
if is_64:
self.sh_entsize = struct.unpack(self.XWord, ifile.read(self.XWordSize))[0]
else:
self.sh_entsize = struct.unpack(self.Word, ifile.read(self.WordSize))[0]
class Elf():
def __init__(self, bfile):
self.bfile = bfile
self.bf = open(bfile, 'r+b')
self.ptrsize = self.detect_elf_type()
init_datasizes(self, self.ptrsize)
self.parse_header()
self.parse_sections()
self.parse_dynamic()
def detect_elf_type(self):
data = self.bf.read(5)
if data[1:4] != b'ELF':
print('File "%s" is not an ELF file.' % self.bfile)
sys.exit(0)
if data[4] == 1:
return 32
if data[4] == 2:
return 64
print('File "%s" has unknown ELF class.' % self.bfile)
sys.exit(1)
def parse_header(self):
self.bf.seek(0)
self.e_ident = struct.unpack('16s', self.bf.read(16))[0]
self.e_type = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_machine = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_version = struct.unpack(self.Word, self.bf.read(self.WordSize))[0]
self.e_entry = struct.unpack(self.Addr, self.bf.read(self.AddrSize))[0]
self.e_phoff = struct.unpack(self.Off, self.bf.read(self.OffSize))[0]
self.e_shoff = struct.unpack(self.Off, self.bf.read(self.OffSize))[0]
self.e_flags = struct.unpack(self.Word, self.bf.read(self.WordSize))[0]
self.e_ehsize = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_phentsize = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_phnum = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_shentsize = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_shnum = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
self.e_shstrndx = struct.unpack(self.Half, self.bf.read(self.HalfSize))[0]
def parse_sections(self):
self.bf.seek(self.e_shoff)
self.sections = []
for i in range(self.e_shnum):
self.sections.append(SectionHeader(self.bf, self.ptrsize))
def read_str(self):
arr = []
x = self.bf.read(1)
while x != b'\0':
arr.append(x)
x = self.bf.read(1)
if x == b'':
raise RuntimeError('Tried to read past the end of the file')
return b''.join(arr)
def find_section(self, target_name):
section_names = self.sections[self.e_shstrndx]
for i in self.sections:
self.bf.seek(section_names.sh_offset + i.sh_name)
name = self.read_str()
if name == target_name:
return i
def parse_dynamic(self):
sec = self.find_section(b'.dynamic')
self.dynamic = []
self.bf.seek(sec.sh_offset)
while True:
e = DynamicEntry(self.bf, self.ptrsize)
self.dynamic.append(e)
if e.d_tag == 0:
break
def print_section_names(self):
section_names = self.sections[self.e_shstrndx]
for i in self.sections:
self.bf.seek(section_names.sh_offset + i.sh_name)
name = self.read_str()
print(name.decode())
def print_soname(self):
soname = None
strtab = None
for i in self.dynamic:
if i.d_tag == DT_SONAME:
soname = i
if i.d_tag == DT_STRTAB:
strtab = i
self.bf.seek(strtab.val + soname.val)
print(self.read_str())
def get_rpath_offset(self):
sec = self.find_section(b'.dynstr')
for i in self.dynamic:
if i.d_tag == DT_RPATH:
return sec.sh_offset + i.val
return None
def print_rpath(self):
offset = self.get_rpath_offset()
if offset is None:
print("This file does not have an rpath.")
else:
self.bf.seek(offset)
print(self.read_str())
def print_deps(self):
sec = self.find_section(b'.dynstr')
deps = []
for i in self.dynamic:
if i.d_tag == DT_NEEDED:
deps.append(i)
for i in deps:
offset = sec.sh_offset + i.val
self.bf.seek(offset)
name = self.read_str()
print(name)
def fix_deps(self, prefix):
sec = self.find_section(b'.dynstr')
deps = []
for i in self.dynamic:
if i.d_tag == DT_NEEDED:
deps.append(i)
for i in deps:
offset = sec.sh_offset + i.val
self.bf.seek(offset)
name = self.read_str()
if name.startswith(prefix):
basename = name.split(b'/')[-1]
padding = b'\0'*(len(name) - len(basename))
newname = basename + padding
assert(len(newname) == len(name))
self.bf.seek(offset)
self.bf.write(newname)
def fix_rpath(self, new_rpath):
rp_off = self.get_rpath_offset()
if rp_off is None:
print('File does not have rpath. It should be a fully static executable.')
return
self.bf.seek(rp_off)
old_rpath = self.read_str()
if len(old_rpath) < len(new_rpath):
print("New rpath must not be longer than the old one.")
self.bf.seek(rp_off)
self.bf.write(new_rpath)
self.bf.write(b'\0'*(len(old_rpath) - len(new_rpath) + 1))
if __name__ == '__main__':
if len(sys.argv) < 2 or len(sys.argv) > 3:
print('This application resets target rpath.')
print('Don\'t run this unless you know what you are doing.')
print('%s: <binary file> <prefix>' % sys.argv[0])
exit(1)
e = Elf(sys.argv[1])
if len(sys.argv) == 2:
e.print_rpath()
else:
new_rpath = sys.argv[2]
e.fix_rpath(new_rpath.encode('utf8'))
#e.fix_deps(prefix.encode())
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