Date: Fri, 15 Jan 2016 16:58:28 -0500 From: Rich Felker <dalias@...c.org> To: oss-security@...ts.openwall.com Subject: Re: Qualys Security Advisory - Roaming through the OpenSSH client: CVE-2016-0777 and CVE-2016-0778 On Fri, Jan 15, 2016 at 01:56:33PM +0100, Yann Droneaud wrote: > Hi, > > Le vendredi 15 janvier 2016 à 12:06 +0100, Florian Weimer a écrit : > > On 01/14/2016 06:13 PM, Qualys Security Advisory wrote: > > > Internal stdio buffering is the most severe of the three problems > > > discussed in this section, although GNU/Linux is not affected > > > because the glibc mmap()s and munmap()s (and therefore cleanses) > > > stdio buffers. > > > > This will change in glibc 2.23, stdio will use regular malloc and > > free for its buffers. I did not expect this change to have security > > implications. Considering that the actual bug lies elsewhere, and > > stdio usage is based on copying out of the buffer (so leaks can still > > happen elsewhere), I do not wish to revert this change. > > > > Would setvbuf(stream, NULL, _IONBF, 0); be used to disable buffer > before reading/writting sensible data to a stream ? Yes. Or preferably you could provide a custom buffer pointer for the stdio FILE to use and clear it safely yourself after calling fclose. > What about a buffering flag (_IOSBF) that would enable "secure" > handling of the buffer, that is, on fclose() and fflush(), write > back and cleanse buffer on output stream, cleanse buffer on input > stream ? This sounds undesirable when there is already a portable fix (above). There are also some issues with compatibility for such a feature between versions and what symbol versioning might be needed. Rich
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