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SubjectCapabilities question
Date
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Hi,

what is the right way to get the current capability setting inherited through
execve()?

My goal is a wrapper program that sets the needed capabilities and then
execve()s the real program. These capabilities should also be inherited if
the real program spawns childs via fork/exec.

Is that possible?

I read the appropriate parts of fs/exec.c where
/*
* This function is used to produce the new IDs and capabilities
* from the old ones and the file's capabilities.
*
* The formula used for evolving capabilities is:
*
* pI' = pI
* (***) pP' = (fP & X) | (fI & pI)
* pE' = pP' & fE [NB. fE is 0 or ~0]
*
* I=Inheritable, P=Permitted, E=Effective // p=process, f=file
* ' indicates post-exec(), and X is the global 'cap_bset'.
*
*/
is implemented. The problem is that fP and fE are either 0 or ~0 depending on
the current uid or the uid of the file to be executed (if S_ISUID). Thus pP'
is only masked by cap_bset which is a global constant (0xfffffeff).

Torsten
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