fsanitize: member access within null pointer

[Pavel Sanda]

On Thu, Dec 16, 2021 at 04:35:39PM +0100, Kornel Benko wrote:
> As strings:
> (gdb) x/10s &addr
> 0x7fffffffd788:	"\001"
> 0x7fffffffd78a:	"/tmp/lyx_tmpdir.kVhnZYL31128/lyxsocket"
> 0x7fffffffd7b1:	""
> 0x7fffffffd7b2:	""
> 0x7fffffffd7b3:	""
> 0x7fffffffd7b4:	""
> 0x7fffffffd7b5:	""
> 0x7fffffffd7b6:	""
> 0x7fffffffd7b7:	""
> 0x7fffffffd7b8:	"|"
> (gdb) 

This looks fine.

Maybe it's because SUN_LEN macro.

In my system I see in /usr/include/x86_64-linux-gnu/sys/un.h
# define SUN_LEN(ptr) ((size_t) (((struct sockaddr_un *) 0)->sun_path)        \
                      + strlen ((ptr)->sun_path))


I guess clang is not happy with (((struct sockaddr_un *) 0)->sun_path)

Our own code has:
#if !defined(SUN_LEN)
#define SUN_LEN(su) \
        (sizeof (*(su)) - sizeof ((su)->sun_path) + strlen((su)->sun_path))
#endif

which does not have this constrt and clang might be happier.
I do not known what headers gets included with clang though.

Pavel