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Standalone portable header-based implementation of FORTIFY_SOURCE=3

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What is it?

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.

Features

  • 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_CHK will make use of compiler-provided builtin _chk functions, which might be a bit better in term of diagnostics, but won't necessarily provide the same amount of security checks.
  • Defining FORTIFY_PEDANTIC_CHECKS will enable pedantic checks, that while technically correct, might break some programs relying on widely accepted undefined-behaviours.

Sample usage

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.

Supported interfaces

  • FD_CLR
  • FD_SET
  • asprintf
  • bcopy
  • bzero
  • calloc
  • confstr
  • fdopen
  • fgets
  • fgetws
  • fmemopen
  • fopen
  • fprintf
  • fread
  • fwrite
  • getcwd
  • getdomainname
  • getgroups
  • gethostname
  • getlogin_r
  • malloc
  • mbsnrtowcs
  • mbsrtowcs
  • mbstowcs
  • memchr
  • memcpy
  • memmove
  • mempcpy
  • memset
  • poll
  • popen
  • ppoll
  • pread
  • printf
  • pwrite
  • qsort
  • read
  • readlink
  • readlinkat
  • realloc
  • reallocarray
  • realpath
  • recv
  • recvfrom
  • select
  • send
  • sendto
  • snprintf
  • sprintf
  • stpcpy
  • stpncpy
  • strcat
  • strchr
  • strcpy
  • strlcat
  • strlcpy
  • strlen
  • strncat
  • strncpy
  • strrchr
  • tmpfile
  • ttyname_r
  • umask
  • vfprintf
  • vprintf
  • vasprintf
  • vsnprintf
  • vsprintf
  • wcrtomb
  • wcscat
  • wcscpy
  • wcsncat
  • wcsncpy
  • wcsnrtombs
  • wcsrtombs
  • wcstombs
  • wctomb
  • wmemcpy
  • wmemmove
  • wmemset
  • write

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Standalone portable header-based implementation of FORTIFY_SOURCE=3

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