3 ms·

I've seen them ask how to restore execution permissions after `chmod a-x /bin/chmod'. I usually answer to those smartasses that I my favourite way is to run the

by dozzie 9y ago

I've seen them ask how to restore execution permissions after `chmod a-x /bin/chmod'. I usually answer to those smartasses that I my favourite way is to run the very non-executable /bin/chmod without any file juggling. I'm yet to meet anybody who wasn't surprised that it's possible.

pnutjam 9y ago
explain?
- shabble 9y ago
  shabble@host:~$ cp /bin/chmod /tmp/chmoo shabble@host:~$ chmod 600 /tmp/chmoo shabble@host:~$ ll /tmp/ch* -rw------- 1 shabble shabble 59K Nov 21 17:15 /tmp/chmoo shabble@host:~$ /tmp/chmoo -bash: /tmp/chmoo: Permission denied shabble@host:~$ /lib64/ld-linux-x86-64.so.2 /tmp/chmoo /tmp/chmoo: missing operand Try '/tmp/chmoo --help' for more information.
  - ansible 9y ago
    Well, that's a new one on me. I'd just have 'cat'ted the chmod executable onto some other executable, which keeps the permissions.
  - AnIdiotOnTheNet 9y ago
    This technique fails if chmod is compiled statically.
- mnarayan01 9y ago
  Manually call e.g. /lib/ld-linux.so.2 (man ld.so for more info).
- jandrese 9y ago
  I'm a little surprised some smartypants hasn't come along and added a check to ld to prevent this from working, probably for "security" reasons. I've known about this trick for a long time, but I've always thought its days were numbered. Another way to solve the problem: scp unfuckedhost:/bin/chmod . ./chmod (stuff)
  - fapjacks 9y ago
    This is my go-to method for doing that. Years ago, in the 90s, I used that trick (with ftp) to overwrite a custom login script used to "prevent" users from logging in. You'd login and it would spit out like "You are not allowed to login!" and then immediately log you out. Well, ftp (this is before sftp or scp) let me copy over that. This was actually one of the computers used by the newspaper in the next town over. I'm still shocked actually that the worst I ever got from the sysadmin there was a stern phone call.

by dozzie 9y ago

pnutjam 9y ago

explain?

shabble 9y ago
shabble@host:~$ cp /bin/chmod /tmp/chmoo shabble@host:~$ chmod 600 /tmp/chmoo shabble@host:~$ ll /tmp/ch* -rw------- 1 shabble shabble 59K Nov 21 17:15 /tmp/chmoo shabble@host:~$ /tmp/chmoo -bash: /tmp/chmoo: Permission denied shabble@host:~$ /lib64/ld-linux-x86-64.so.2 /tmp/chmoo /tmp/chmoo: missing operand Try '/tmp/chmoo --help' for more information.
- ansible 9y ago
  Well, that's a new one on me. I'd just have 'cat'ted the chmod executable onto some other executable, which keeps the permissions.
- AnIdiotOnTheNet 9y ago
  This technique fails if chmod is compiled statically.
mnarayan01 9y ago
Manually call e.g. /lib/ld-linux.so.2 (man ld.so for more info).
jandrese 9y ago
I'm a little surprised some smartypants hasn't come along and added a check to ld to prevent this from working, probably for "security" reasons. I've known about this trick for a long time, but I've always thought its days were numbered. Another way to solve the problem: scp unfuckedhost:/bin/chmod . ./chmod (stuff)
- fapjacks 9y ago
  This is my go-to method for doing that. Years ago, in the 90s, I used that trick (with ftp) to overwrite a custom login script used to "prevent" users from logging in. You'd login and it would spit out like "You are not allowed to login!" and then immediately log you out. Well, ftp (this is before sftp or scp) let me copy over that. This was actually one of the computers used by the newspaper in the next town over. I'm still shocked actually that the worst I ever got from the sysadmin there was a stern phone call.