Resolving a username to uid/gid read /etc/passwd and /etc/group via
os.Open with no upper bound, letting a crafted image force unbounded
memory use during user resolution. Cap reads at 10MiB and reject
non-regular files in both the OCI executor and the chown user resolver.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
(cherry picked from commit 83cfc1e0ea1dcf8816f259ee6720b8694ab874e5)
408266e4ba