tree 982fc13c9b21b84105d083ae26e690c3c7e23bba
parent bb0a7642d63b95a0f7db23f38d7f1c957930ec08
author Daniel Rosenberg <drosen@google.com> 1630614483 -0700
committer Daniel Rosenberg <drosen@google.com> 1630617209 -0700

snapuserd: Fix PrepareReadAhead

When checking the instead of current, and when checking the position, we could underflow,
which would get caught by UBSAN

Bug: 177104308
Test: Map cow file with xor op or copy op at position 0
Change-Id: I4fba1982419e08b58759ec893e238175d245dbfc