CVE request: kernel: don't allow splice() to files opened with O_APPEND

[Eugene Teo <eteo () redhat com>]

This was committed in upstream kernel recently.

"[PATCH] Don't allow splice() to files opened with O_APPEND

This is debatable, but while we're debating it, let's disallow the
combination of splice and an O_APPEND destination.

It's not entirely clear what the semantics of O_APPEND should be, and
POSIX apparently expects pwrite() to ignore O_APPEND, for example.  So
we could make up any semantics we want, including the old ones.

But Miklos convinced me that we should at least give it some thought,
and that accepting writes at arbitrary offsets is wrong at least for
IS_APPEND() files (which always have O_APPEND set, even if the reverse
isn't true: you can obviously have O_APPEND set on a regular file).

So disallow O_APPEND entirely for now.  I doubt anybody cares, and this
way we have one less gray area to worry about."

Upstream commit: efc968d450e013049a662d22727cf132618dcb2f

Files opened with O_APPEND are ignored. This could allow users to bypass
the append-only restriction. This probably needs a CVE name.

Thanks, Eugene