I am currently reverse a challenge to learn. But why is the parameter of mmap (containing
fd) at 4294967295?
(Is it not supposed to exist? No files are open with
open, just before.)
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void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);
4294967295 is same as -1 when treated as a signed integer.
mmap calls actually looks like
mmap( NULL, /*addr*/ 321, /*length*/ PROT_EXEC | PROT_READ | PROT_WRITE, /*prot*/ MAP_ANONYMOUS | MAP_PRIVATE, /*flags*/ -1, /*fd*/ 0 /*offset*/ )
Now as per the man pages,
The mapping is not backed by any file; its contents are initialized to zero. The fd and offset arguments are ignored; however, some implementations require fd to be -1 if MAP_ANONYMOUS (or MAP_ANON) is specified, and portable applications should ensure this. The use of MAP_ANONYMOUS in conjunction with MAP_SHARED is only supported on Linux since kernel 2.4.
It says if
MAP_ANONYMOUS is specified then we may use
fd which explains your question.