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SubjectRe: overlayfs: caller_credentials option bypass creator_cred
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On 06/18/2018 12:43 PM, Vivek Goyal wrote:
> Will it be acceptable to write security policies in such a way so that
> mounter has access as well.
Unfortunately No. Policy of minimizing attack surface for a contained
root service (init in this case). Just because it can mount, does not
mean it can modify critical content; an attacker could use this to open
a hole.

> Current model does assume that mounter has privileges on underlying files.

Only ones it appears to need is the workdir AFAIK, had to add ability to
create in the <wordir> xattr in order to enable r/w mounts later.
Although not all corners were tested, I did not see any copy_up issues
b/c the caller had the privs in the Android security model when mounted
with this new flag.

-- Mark

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