samba-4.1.11\lib\util\string_wrappers.h

line 49:

#define nstrcpy(d,s) \
do { \
	const char *_nstrcpy_src = (const char *)(s); \
	strlcpy((d),_nstrcpy_src ? _nstrcpy_src : "",sizeof(fstring)); \
} while (0)


nstrcpy is intended for use on typedef nstring which has len 16:

#define MAX_NETBIOSNAME_LEN 16
typedef char nstring[MAX_NETBIOSNAME_LEN];

fstring is 256 bytes.

Using nstrcpy() will allow 256 bytes to be copied into a buffer of only 16 bytes, leading to a stack overflow.