A question about modifying the buffer under authenticated encryption

[Mikulas Patocka <mpatocka@redhat.com>]

Hi

I'm trying to fix some problems in dm-crypt that it may report 
authentication failures when the user reads data with O_DIRECT and 
modifies the read buffer while it is being read.

I'd like to ask you:

1. If the authenticated encryption encrypts a message, reading from 
   buffer1 and writing to buffer2 - and buffer1 changes while reading from 
   it - is it possible that it generates invalid authentication tag?

2. If the authenticated encryption decrypts a message, reading from 
   buffer1 and writing to buffer2 - and buffer2 changes while writing to 
   it - is is possible that it reports authentication tag mismatch?

Mikulas