ld.so clears TMPDIR for setuid programs

[Andrew Pimlott]

[ I tried to send this with glibcbug, but it sent to
address@hidden which seems to be a black hole at
the moment. ]

ld.so unsets some envionment variables when running setuid programs,
including some widely used ones like TMPDIR.  Further, the behavior
is not documented.  This caused me great frustration in trying to
track down a problem.

I assume glibc does this to prevent its own internal use of these
variables.  While this may be acceptible for glibc-specific
variables, I think it's too surprising for variables used by other
programs.  If it's really necessary for glibc to ignore TMPDIR (not
sure why), maybe it can set a flag indicating that it's running
setuid, and check that.

I'm using libc6 2.3.2-2 from Debian testing.

Andrew