linux - [Solved-6 Solutions] What is the LD_PRELOAD trick ? - ubuntu - red hat - debian - linux server - linux pc
Linux - Problem :
What is the LD_PRELOAD trick ?
Linux - Solution 1:
- LD_PRELOAD is an environment variable.
- check for the LD_PRELOAD environment variable, and complain (though the attacker could also LD_PRELOAD the function that lets you read environment variables.
Linux - Solution 2:
- If you set LD_PRELOAD to the path of a shared object, that file will be loaded before any other library (including the C runtime, libc.so).
- To run ls with your special malloc() implementation, do this:
$ LD_PRELOAD=/path/to/my/malloc.so /bin/lsclick below button to copy the code. By - Linux tutorial - team
Linux - Solution 3:
- You can override symbols in the stock libraries by creating a library with the same symbols and specifying the library in LD_PRELOAD.
Linux - Solution 4:
LD_PRELOAD you can give libraries priority.
For instance you can write a library which implement malloc and free. Also, by Loading these with LD_PRELOAD your malloc and free will be executed rather than the standard ones.
Linux - Solution 5:
Using LD_PRELOAD to preload library. You can check if the setting is available by ldd command.
Example: suppose you need to preload your own libselinux.so.1.
> ldd /bin/ls
...
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f3927b1d000)
libacl.so.1 => /lib/x86_64-linux-gnu/libacl.so.1 (0x00007f3927914000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f392754f000)
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f3927311000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f392710c000)
/lib64/ld-linux-x86-64.so.2 (0x00007f3927d65000)
libattr.so.1 => /lib/x86_64-linux-gnu/libattr.so.1 (0x00007f3926f07000)click below button to copy the code. By - Linux tutorial - team
Set your preload environment:
export LD_PRELOAD=/home/patric/libselinux.so.1click below button to copy the code. By - Linux tutorial - team
Again Check your library:
>ldd /bin/ls
...
libselinux.so.1 =>
/home/patric/libselinux.so.1 (0x00007fb9245d8000)
...click below button to copy the code. By - Linux tutorial - team
Linux - Solution 6:
Export mylib.so to env:
$ export LD_PRELOAD=/path/mylib.so
$ ./mybinclick below button to copy the code. By - Linux tutorial - team
To disable :
$ export LD_PRELOAD=