On Mon, Feb 27, 2017 at 10:57 AM, Michael Kerrisk
[off-list ref] wrote:
[CC += linux-api@vger.kernel.org]
Hi Willem
quoted
On a send call with MSG_ZEROCOPY, the kernel pins the user pages and
creates skbuff fragments directly from these pages. On tx completion,
it notifies the socket owner that it is safe to modify memory by
queuing a completion notification onto the socket error queue.
What happens if the user writes to the pages while it's not safe?
How about if you're writing to an interface or a route that has crypto
involved and a malicious user can make the data change in the middle
of a crypto operation, thus perhaps leaking the entire key? (I
wouldn't be at all surprised if a lot of provably secure AEAD
constructions are entirely compromised if an attacker can get the
ciphertext and tag computed from a message that changed during the
computation.
I can see this working if you have a special type of skb that
indicates that the data might be concurrently written and have all the
normal skb APIs (including, especially, anything that clones it) make
a copy first.
--Andy