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On 09/06/2017 02:46 PM, up201407890@alunos.dcc.fc.up.pt wrote: What are your thoughts on adding a SAFE_FREE() macro to glibc:
#define SAFE_FREE(x) do { if((x) != 0x0) { free(x); (x) = (void *)0x1; }} while(0)
After free(x), we set x to an address that will crash when dereferenced (use-after-free), and will also crash when it's an argument to free(). Note that NULL isn't used, because free(NULL) does nothing, which mighthide potential double-free bugs.
Maybe GCC should optionally do this for the actual call to free. Thereis some debate to what extend pointer *values* remain valid after free.Martin Sebor may have some thought on that.
In any case, some GCC assistance is needed so that
free (some_struct->ptr); free (some_struct);
actually clobbers some_struct->ptr. I don't think we want to call out to explicit_bzero here.
One of the advantages of doing this in the compiler (besides not having to change source code) is distinguishing rvalues from lvalues.
Martin
Perhaps this sould be used when making use of FORTIFY_SOURCE? Federico.
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