Stack clash is a vulnerability published in June 2017 by Qualys.
As mentioned in their detailed advisory, this is actually an old vulnerability, with a first public exploit by Gael Delalleau, dating back to 2005, and as mentioned on grsecurity’s article An Ancient Kernel Hole is (Not) Closed, there was even a patch available in 2004 to mitigate it.
In August 2010, Linus Torvald added a 4k guard page between the heap and the stack in the Linux kernel as a possible mitigation.
Unfortunately, this wasn’t enough to mitigate the issue, since it’s possible to jump over the guard page.
It’s interesting to note that grsecurity wasn’t vulnerable.
In Qualy’s advisory,
-fstack-check was recommended as a better mitigation,
but apparently it’s also
-fstack-clash-protection option, added in gcc8,
taking inspiration from Microsoft’s Windows (which was never affected),
is the best solution. It’s currently enabled since Fedora
SUSE 15, …
and will be enabled by default in Ubuntu
but not in Debian.
OpenBSD’s fork of gcc is too
old to have this feature backported,
and as for clang, it’s not there yet.