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Re: issetugid?

On 07/16/2014 07:53 PM, Rich Felker wrote:
This is a very good point. The LibreSSL folks are claiming that
getauxval(AT_SECURE) is not safe due to the lack of any way to detect
bug #15846 at runtime (and trying to use a strverscmp against the
glibc version string as a way to know if the bug is present...).
However, I think they're wrong because AT_SECURE is always included in
the aux vector for all kernels glibc supports; ENOENT cannot happen.

Yes, this is a bit like complaining that getpid has no error return value.

And if there were a way to suppress AT_SECURE, it would affect
LD_PRELOAD etc. anyway and thus already be a vulnerability independent
of getauxval's reporting of errors.

I don't think prctl(PR_GET_DUMPABLE) is relevant or useful for this
since it would have to be tested at startup before any application
code runs in order to reflect the AT_SECURE status.

See below; this is related to the issetugid differences.

What's worse, the Solaris and FreeBSD versions of issetugid are
different, so we'd have to pick one behavior and be incompatible
with the other.

Could you explain how they differ? I'm reading the Solaris
documentation here:

and it appears to match the semantics that were proposed for addition
to musl.

FreeBSD's issetugid returns true if the process has altered any of the UIDs/GIDs after it has been created ("if it has changed any of its real, effective or saved user or group ID's since it began execution"). In contrast, the Solaris manpage is unaffected by ID changes ("The result of a call to issetugid() is unaffected by calls to setuid(), setgid(), or other such calls.").

So FreeBSD issetugid is like prctl(PR_GET_DUMPABLE), and Solaris issetugid is like getauxval(AT_SECURE).

Florian Weimer / Red Hat Product Security

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