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Comment by DisposaBoy | Hacker News Reader

For what it's worth, I get the error: ln: failed to create hard link `/tmp/exploit/target' => `/bin/ping': Invalid cross-device link

Are there any other way to do this without ln? I have no binaries on non-root-writable filesystems. tmp is on tmpfs, / and /home are on their own filesystems so I'd need to be root to create the files on a partition that this could work from.

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Doesn't sound like it. Sounds like you need a setuid binary on a filesystem you can link to.

You can use find to see if you have a setuid binary anywhere in your filesystem:

    find / -perm -4000 2>/dev/null

Your /tmp is on a separate file system than /bin. _Hard_ links point to the same inode, therefore both parts of your link must be on the same file system (as opposed to a soft link, which is a separate inode saying "hey buddy, go over there").

It might work in something like /var/tmp, assuming that's not a soft link to /tmp like some systems do, or a separate file system.

No. You have one of the workarounds the author suggests, which is only allowing users to write to nosuid mounts.

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