Messages in this thread | | | Date | Tue, 17 Apr 2007 23:48:01 +0400 | From | Michael Tokarev <> | Subject | Wondering: why capabilities system is broken? |
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Hopefully not a flamewar question...
Currently, capabilities of a process are reset during exec() system call. At least effective+permitted set.
1) In case new uid != 0, all the caps are cleared, so it is not possible to execute a program as non-root but still give it some capabilities (like, say, CAP_NET_BIND_SERVICE).
2) In case new uid == 0, effective and permitted sets are restored to all-ones.
This is regardless of other settings, like prctl(KEEPCAPS), or the current set of capabilities.
I partly understand why 2) is done - in case of setuid binary being executed, all the capabilities are set for it. But this breaks executing non-setuid binaries too -- for example, it'd be very nice to be able to chroot to some directory, and remove CAP_SYS_CHROOT (and other evil caps like CAP_SYS_MODULE, CAP_SETPCAP) -- this way, with minimal efforts, chroot will work almost (yes, I understand it's not entirely the same) the same as BSD jail(2) concept.
So the question is: why capability sets are being reinitialized during exec()? At least in 2.4 era, they weren't... and stuff like execcap, sucaps etc was working. Now they aren't anymore.
Thanks.
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