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Subjectcaps in elf headers: use the sticky bit!
Hi all,
Geez, instead of overloading the meaning of 'setuid 0', let's just
use the sticky bit! I.e., sticky bit==cap flag:

- To set the cap flag, a user (process) needs CAP_SETFCAP raised, and the
kernel (besides the normal fs checks) validates the cap headers as well
for legality. (this also applies to creating files with this flag raised;
i.e., through a copy operation)
- While the cap flag is set, the file is immutable, so the file owner
can't edit the file directly to raise caps.
- A file that is both setuid root and capability enabled has only those
capabilities granted in conjuction w/ the headers; if it's only setuid
root, the kernel can (as a configurable option?) treat it as before and
raise all caps.

This can bring us _really_ close to true capabilities support,
while avoiding the ugly hack of also storing uid + suid bit in the elf
headers.

thoughts?

- --
David L. Parsley
Network Specialist
City of Salem Schools


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