capng_change_id - change the credentials retaining capabilities
#include <cap-ng.h>
int capng_change_id(int uid, int gid, capng_flags_t flag);
This function will change uid and gid to the ones given while retaining the
capabilities previously specified in capng_update. It is also possible to
specify -1 for either the uid or gid in which case the function will not
change the uid or gid and leave it "as is". This is useful if you
just want the flag options to be applied (assuming the option doesn't require
more privileges that you currently have).
It is not necessary and perhaps better if capng_apply has not been called prior
to this function so that all necessary privileges are still intact. The caller
may be required to have CAP_SETPCAP capability still active before calling
this function or capabilities cannot be changed.
This function also takes a flag parameter that helps to tailor the exact actions
performed by the function to secure the environment. The option may be or'ed
together. The legal values are:
- CAPNG_NO_FLAG
- Simply change uid and retain specified capabilities and
that's all.
- CAPNG_DROP_SUPP_GRP
- After changing id, remove any supplement groups that may
still be in effect from the old uid.
- CAPNG_INIT_SUPP_GRP
- After changing id, initialize any supplement groups that
may come with the new account. If given with CAPNG_DROP_SUPP_GRP it
will have no effect.
- CAPNG_CLEAR_BOUNDING
- Clear the bounding set regardless to the internal
representation already setup prior to changing the uid/gid.
- CAPNG_CLEAR_AMBIENT
- Clear ambient capabilities regardless of the internal
representation already setup prior to changing the uid/gid.
This returns 0 on success and a negative number on failure.
- -1 means capng has not been initted properly
- -2 means a failure requesting to keep capabilities across
the uid change
- -3 means that applying the intermediate capabilities
failed
- -4 means changing gid failed
- -5 means dropping supplemental groups failed
- -6 means changing the uid failed
- -7 means dropping the ability to retain caps across a uid
change failed
- -8 means clearing the bounding set failed
- -9 means dropping CAP_SETPCAP or ambient capabilities
failed
- -10 means initializing supplemental groups failed
Note: the only safe action to do upon failure of this function is to probably
exit. This is because you are likely in a situation with partial permissions
and not what you intended.
capng_update(3),
capng_apply(3),
prctl(2),
capabilities(7)
Steve Grubb