On Tue, Jul 25, 2006 at 01:47:19PM -0500, Serge E. Hallyn wrote: > Quoting Frank v Waveren ([email protected]): > > While debugging an odd problem where /proc/sys/kernel/cap-bound wasn't > > working, I came across the following code at > > linux-2.6.x/security/commoncap.c:140: > > > > void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe) > > { > > /* Derived from fs/exec.c:compute_creds. */ > > kernel_cap_t new_permitted, working; > > > > new_permitted = cap_intersect (bprm->cap_permitted, cap_bset); > > working = cap_intersect (bprm->cap_inheritable, > > current->cap_inheritable); > > new_permitted = cap_combine (new_permitted, working); > > ... > > > > Here the new permitted set gets limited to the bits in cap_bset, which > > is as it should be, but then the intersection of the of the current > > and exec inheritable masks get added to that set, whereas as I > > understand it, cap_bset should always be the bounding set. > [...] > > Actually going by the faq > (http://ftp.kernel.org/pub/linux/libs/security/linux-privs/kernel-2.4/capfaq-0.2.txt) > it seems like the cap_intersect with current->cap_inheritable is *too* > limiting. I haven't checked what the posix draft actually says, but the > bprm->cap_inheritable is called the 'forced' set, and is supposed to be > like setuid. I don't think the force set should be able to override the cap bound though. Like the force/setuid analogy, I think we can compare the cap_bset to the old securelevel system, which means that it should be the bounding factor. Even if you have setuids on a system with a raised securelevel, they still can't do the restricted operations. Once again, this is not based on what the POSIX 1003.1e says, as a matter of fact I can't find anything about lowering the systemwide bound externally (as opposed to by not having forced-set executables and dropping the caps from all processes) at all in a quick grep of the document, so I suspect this is entirely outside of the spec anyway. -- Frank v Waveren Key fingerprint: BDD7 D61E [email protected] 5D39 CF05 4BFC F57A Public key: hkp://wwwkeys.pgp.net/468D62C8 FA00 7D51 468D 62C8
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