FreeBSD: VID-ddecde18-e33b-11e7-a293-54e1ad3d6335 (CVE-2017-16612): libXcursor -- integer overflow that can lead to heap buffer overflow

The freedesktop.org project reports: It is possible to trigger heap overflows due to an integer overflow while parsing images and a signedness issue while parsing comments. The integer overflow occurs because the chosen limit 0x10000 for dimensions is too large for 32 bit systems, because each pixel takes 4 bytes. Properly chosen values allow an overflow which in turn will lead to less allocated memory than needed for subsequent reads. The signedness bug is triggered by reading the length of a comment as unsigned int, but casting it to int when calling the function XcursorCommentCreate. Turning length into a negative value allows the check against XCURSOR_COMMENT_MAX_LEN to pass, and the following addition of sizeof (XcursorComment) + 1 makes it possible to allocate less memory than needed for subsequent reads.