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    SubjectRe: mmap bug?
    On 29 May 1998, Ben Pfaff wrote:

    > It seems that attempts to mmap a region of size zero causes
    > mmap to return zero. Is this a bug?
    >
    > Since it doesn't return -1, it looks like success, but of
    > course dereferencing this NULL pointer causes a crash.
    >
    > Why would you dereference it if you didn't specify any memory? It
    > seems to me that this is valid kernel behavior, and that the program
    > has the bug.

    The program, in this case, is glibc.

    It is mmapping a file which it has been told by stat() is zero length.

    I was just curious as to whether Unix98 or similar specifies any
    behaviour; nowhere in the man page is the possibility of a zero return
    from mmap mentioned. This is a free segfault out of many programs; of
    course, as a NULL pointer dereference, it's not exactly dangerous.

    FWIW, Solaris (x86 and Sparc) returns -1 and sets errno to EINVAL.
    Digital Unix returns -1 and ENXIO.

    Matthew.


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