1

While trying to learn about how ld-2.17.so works to change the permission of chmod executable itself, and thought if i can change the permission of ld-2.17.so itself.

I ran chmod 666 ld-2.17.so in a test centos 7 machine and after it I can't run any command since most of the commands use ld-2.17.so.

I have already read this answer, Recovering from removing execute permission from ld-linux.so

It gives a very general answer but not a specific solution. Is there anywhere in Centos7 i can find ld-2.17.so cache to recover /lib64/ld-2.17.so permission back to normal?

Edit: I have tried to scp this file, /lib64/ld-2.17.so from other machine to affected machine, but I get permission denied error.

Thank you in advance

MaverickD
  • 359

1 Answers1

3

If you have an executable file you can write to, you could copy the contents of ld.so to that file using bash's read:

while IFS= read -d '' -r  line; do printf "%s\0" "$line"; done > executable-file < /lib64/ld-2.17.so

Example: 

bash-4.2$ ll foo
-rwxr-xr-x 1 muru muru 29K Aug 23 13:02 foo*
bash-4.2$ while IFS= read -d '' -r  line; do printf "%s\0" "$line"; done > foo < /lib64/ld-2.17.so
bash-4.2$ ./foo
Usage: ld.so [OPTION]... EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]
You have invoked `ld.so', the helper program for shared library executables.
...

Then you can use it to run chmod:

bash-4.2$ ./foo /bin/chmod
/bin/chmod: missing operand
Try '/bin/chmod --help' for more information.
muru
  • 72,889
  • Thankk you muru. That's really helpful. Could you please suggest if i don't have any sample executable available is there any unused executable that I can use from within Linux? One more question, how do you know bash's read doesn't used dynamic libraries. thank you – MaverickD Aug 23 '18 at 07:56
  • 1
    @MaverickD the assumption here is that you already have a running shell from before you messed up ld.so. If you don't, and you don't have a statically compiled shell (like busybox) available, you have to reboot and use recovery methods, plain and simple. As for sample executables, pick any except chmod and then reinstall that command later once you have fixed ld.so. (or you can save the contents to a different file, using the same read method) – muru Aug 23 '18 at 07:58