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(Kees Cook) Like all C/C++ programs, the Linux Kernel regularly suffers from buffer overflow flaws. While stack overflows have been largely addressed, heap overflows remain common. Especially frustrating is that the compiler usually has enough context to have been able to stop the overflow but C APIs are so terrible that it doesn't happen.

We'll take a quick look back through at least the last 3 years of heap buffer overflow CVEs in the kernel. This will lead to the discovery that all 11 memcpy overflows from this timespan (which includes the heap buffer overflow flaw used by the BleedingTooth exploit), could have been detected and mitigated by the compiler. However, limitations in C language usage, APIs, kernel coding conventions, and compiler bugs made this a difficult problem to tackle.

We will explore the path to solutions being developed in the Linux kernel for dealing with array index overflows, string manipulation overflows, and especially memcpy overflows. We will cover the history of C flexible arrays, the unexpected places where the "-Warray-bounds" and "-fsanitize=bounds" compiler options don't work, the limits of "__builtin_object_size" (the work-horse of FORTIFY_SOURCE), and how memcpy is being effectively replaced to stop overflows from ever happening again.

https://lca2022.linux.org.au/schedule/presentation/27/

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Sat Jan 15 10:45:00 2022 at Kaya Theatre