This is a standalone implementation of
fortify source
level 3, providing compile time security checks.
It is libc-agnostic and simply overlays the system headers by using the
#include_next
extension found in GCC, and
black magic
on Clang. It was initially intended to be used on
musl based
Linux distributions.
- It is portable, works on *BSD, Linux, Solaris and possibly others.
- It will only trap non-conformant programs. This means that fortify level 2 is treated in the same way as level 1.
- Avoids making function calls when undefined behaviour has already been
invoked. This is handled by using
__builtin_trap(). - Support for out-of-bounds read interfaces, such as send(), write(), fwrite() etc.
- No ABI is enforced. All of the fortify check functions are inlined into the resulting binary.
- It has a comprehensive suite of tests, running both on Clang and on GCC for every commit, on C89, C99, C11 and C17, with significant coverage
- Defining
FORTIFY_USE_NATIVE_CHKwill make use of compiler-provided builtin_chkfunctions, which might be a bit better in term of diagnostics, but won't necessarily provide the same amount of security checks. - Defining
FORTIFY_PEDANTIC_CHECKSwill enable pedantic checks, that while technically correct, might break some programs relying on widely accepted undefined-behaviours.
If you want to quickly test it, you can try something like the following:
cat > fgets.c <<EOF
#include <stdio.h>
int
main(void)
{
char buf[BUFSIZ];
fgets(buf, sizeof(buf) + 1, stdin);
return 0;
}
EOF
cc -I<path-to-fortify-include-dir> -D_FORTIFY_SOURCE=3 -O1 fgets.c
./a.out
At this point, the program will safely and loudly crash.
FD_CLRFD_SETasprintfbcopybzerocallocconfstrfdopenfgetsfgetwsfmemopenfopenfprintffreadfwritegetcwdgetdomainnamegetgroupsgethostnamegetlogin_rmallocmbsnrtowcsmbsrtowcsmbstowcsmemchrmemcpymemmovemempcpymemsetpollpopenppollpreadprintfpwriteqsortreadreadlinkreadlinkatreallocreallocarrayrealpathrecvrecvfromselectsendsendtosnprintfsprintfstpcpystpncpystrcatstrchrstrcpystrlcatstrlcpystrlenstrncatstrncpystrrchrtmpfilettyname_rumaskvfprintfvprintfvasprintfvsnprintfvsprintfwcrtombwcscatwcscpywcsncatwcsncpywcsnrtombswcsrtombswcstombswctombwmemcpywmemmovewmemsetwrite