ipc: fix potential oops when src msg > 4k w/ MSG_COPY

ipc: fix potential oops when src msg > 4k w/ MSG_COPY

commit e1082f45f1e2bbf6e25f6b614fc6616ebf709d19 upstream.

If the src msg is > 4k, then dest->next points to the
next allocated segment; resetting it just prior to dereferencing
is bad.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>