Fix/linux env/readlink

[Sh3idan]

Fix sandbox escape.

case 1

My architecture:

file_sb/
├── home
│   └── user
│       └── bin.elf
└── proc
    ├── 1000
    │   └── exe -> ../../home/user/bin.elf
    └── self -> 1000

FileSystem::resolve_path returns non-sandboxed path if path parameter is a symbolic link and follow_link is False. See below:

[syscalls][sys_x86_64_readlink][DEBUG]: sys_readlink('/proc/self/exe', 13f028, fff)
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=False)
[environment][resolve_path][DEBUG]: -> 'home/user/bin.elf'
[syscalls][syscall_x86_64_exception_handler][DEBUG]: -> ffffffffffffffff

case 2

file_sb/
├── home
│   └── user
│       └── bin.elf
└── proc
    ├── 1000
    │   └── exe -> ../../../../home/user/bin.elf
    └── self -> 1000

Second case:

[syscalls][sys_generic_open][DEBUG]: sys_open('/proc/self/exe', 0, 0)
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=True)
[environment][resolve_path][DEBUG]: resolve_path(path='../../home/user/bin.elf', follow_link=True)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/../../home/user/bin.elf'
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/../../home/user/bin.elf'
[syscalls][syscall_x86_64_exception_handler][DEBUG]: -> ffffffffffffffff

...

[syscalls][sys_x86_64_readlink][DEBUG]: sys_readlink('/proc/self/exe', 13f028, fff)
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=False)
[environment][resolve_path][DEBUG]: -> '../../home/user/bin.elf'
[syscalls][syscall_x86_64_exception_handler][DEBUG]: -> ffffffffffffffff

Current behavior

try to solve relative link targeting something in the sandbox

[environment][readlink][DEBUG]: readlink('/proc/self/exe')
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/proc/self/exe'
[environment][resolve_path][DEBUG]: resolve_path(path='/home/bla/[TRUNCATED]/file_sb/home/user/bin.elf', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/home/user/bin.elf'
[environment][readlink][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/home/user/bin.elf'
[syscalls][syscall_x86_64_exception_handler][DEBUG]: -> 4b

try to solve relative link targeting something out of sandbox

[environment][readlink][DEBUG]: readlink('/proc/self/exe')
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/proc/self/exe'
[environment][resolve_path][DEBUG]: resolve_path(path='/home/bla/[TRUNCATED]/bin.elf', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/home/bla/[TRUNCATED]/chal/home/user/bin.elf'
[environment][readlink][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/home/bla/[TRUNCATED]/chal/home/user/bin.elf'

try to solve absolute link targeting something in the sandbox

[environment][readlink][DEBUG]: readlink('/proc/self/exe')
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/proc/self/exe'
[environment][resolve_path][DEBUG]: resolve_path(path='/home/bla/[TRUNCATED]/file_sb/home/user/bin.elf', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/home/user/bin.elf'
[environment][readlink][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/home/user/bin.elf'

try to solve absolute link targting something out of the sandbox

[syscalls][sys_generic_open][DEBUG]: sys_open('/proc/self/exe', 0, 0)
[environment][resolve_path][DEBUG]: resolve_path(path='/proc/self/exe', follow_link=True)
[environment][readlink][DEBUG]: readlink('/home/bla/[TRUNCATED]/file_sb/proc/self/exe')
[environment][resolve_path][DEBUG]: resolve_path(path='/home/bla/[TRUNCATED]/file_sb/proc/self/exe', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/proc/self/exe'
[environment][resolve_path][DEBUG]: resolve_path(path='/tmp', follow_link=False)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/tmp'
[environment][readlink][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/tmp'
[environment][resolve_path][DEBUG]: resolve_path(path='/home/bla/[TRUNCATED]/file_sb/tmp', follow_link=True)
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/tmp'
[environment][resolve_path][DEBUG]: -> '/home/bla/[TRUNCATED]/file_sb/tmp'
[syscalls][syscall_x86_64_exception_handler][DEBUG]: -> ffffffffffffffff