std::io::PathWalk container overflow with sanitizer

[alexveden]

Consider this sample example:

fn void! AstProject.load(&self) {
    if (self.proj_path) {
        path::Path p = path::temp_new(self.proj_path)!;
        if (!path::is_dir(p)) {
            return IoError.FILE_NOT_DIR?;
        }

        path::PathWalker fnwalk = fn bool!(Path p, bool is_dir, void* ctx) {
            AstProject* self = (AstProject*)ctx;
            if (is_dir) return false;

            return false;
        };
        p.walk(fnwalk, self)!!;
    }
}

With sanitizer, it fails at:

==3625966==ERROR: AddressSanitizer: container-overflow on address 0x7ffc2d7b2f18 at pc 0x7f0b91cb6c25 bp 0x7ffc2d7b2cd0 sp 0x7ffc2d7b2480
WRITE of size 16 at 0x7ffc2d7b2f18 thread T0
    #0 0x7f0b91cb6c24 in __asan_memcpy ../../../../src/libsanitizer/asan/asan_interceptors_memintrinsics.cpp:22
    #1 0x557436aa1729 in std.io.path.PathImp.new_append /home/ubertrader/code/c3c/lib/std/io/path.c3
    #2 0x557436aa4b20 in std.io.path.PathImp.walk /home/ubertrader/code/c3c/lib/std/io/path.c3:561
    #3 0x557436aa4e8c in std.io.path.PathImp.walk /home/ubertrader/code/c3c/lib/std/io/path.c3:564
    #4 0x557436ae3f23 in c3tools.ast.AstProject.load /home/ubertrader/code/c3test/lib/c3tools/ast.c3:323
    #5 0x557436ae4406 in c3symbols.process_dir /home/ubertrader/code/c3test/src/c3symbols.c3:10
    #6 0x557436ae4d9e in c3symbols.main /home/ubertrader/code/c3test/src/c3symbols.c3:94
    #7 0x557436ae5746 in @main_to_int_main_args /home/ubertrader/code/c3c/lib/std/core/private/main_stub.c3:47
    #8 0x557436ae5746 in main /home/ubertrader/code/c3test/src/c3symbols.c3:69
    #9 0x7f0b91967249 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #10 0x7f0b91967304 in __libc_start_main_impl ../csu/libc-start.c:360
    #11 0x557436a2e490 in _start (/home/ubertrader/code/c3test/build/c3symbols+0x1d490)

I think it caused by this line: https://github.com/c3lang/c3c/blob/master/lib/std/io/path.c3#L554, maybe stack overflow?

Another proposal: can we replace void* by any? I segfaulted when passed p.walk(fnwalk, &self)!!; instead of p.walk(fnwalk, self)!!;

def PathWalker = fn bool! (Path, bool is_dir, void*);

[lerno]

Since you're passing self using &self it's already a AstProject* so when you take the address of that, you're passing an AstProject** which you then cast to AstProject* which isn't great.

Also, because it is void*, this is sufficient: AstProject* self = ctx;

[lerno]

As for the overflow I'm somewhat at a loss where this happens here. We don't see the actual allocation.