One problem with libkcapi is that it's abusing vmsplice(). It must not use
vmsplice(SPLICE_F_GIFT) on a buffer that's in the heap. To quote the manual
page:
The user pages are a gift to the kernel. The application may
not modify this memory ever, otherwise the page cache and on-
disk data may differ. Gifting pages to the kernel means that a
subsequent splice(2) SPLICE_F_MOVE can successfully move the
pages; if this flag is not specified, then a subsequent
splice(2) SPLICE_F_MOVE must copy the pages. Data must also be
properly page aligned, both in memory and length.
Basically, this can destroy the integrity of the process's heap as the
allocator may have metadata there that then gets excised.
If I remove the flag, it still crashes, so that's not the only problem.
David
