pkg/shortnames

Add a new package for short-name resolution. `pkg/shortnames` is built
around the short-name aliasing in the registries.conf and introduces two
functions.

Signed-off-by: Valentin Rothberg <[email protected]>

docs/containers-registries.conf.5.md

@@ -102,6 +102,75 @@ internet without having to change `Dockerfile`s, or to add redundancy).
 *Note*: Redirection and mirrors are currently processed only when reading images, not when pushing
 to a registry; that may change in the future.
 
+#### Short-Name Aliasing
+The use of unqualified-search registries entails an ambiguity as it is
+unclear from which registry a given image, referenced by a short name,
+may be pulled from.
+
+As mentioned in the note at the end of this man page, using short names is
+subject to the risk of hitting squatted registry namespaces. If the
+unqualified-search registries are set to `["registry1.com", "registry2.com"]`
+an attacker may take over a namespace of registry1.com such that an image may
+be pulled from registry1.com instead of the intended source registry2.com.
+
+While it is highly recommended to always use fully-qualified image references,
+existing deployments using short names may not be easily changed. To
+circumvent the aforementioned ambiguity, so called short-name aliases can be
+configured that point to a fully-qualified image
+reference.
+
+Short-name aliases can be configured in the `[aliases]` table in the form of
+`"name"="value"` with the left-hand `name` being the short name (e.g., "image")
+and the right-hand `value` being the fully-qualified image reference (e.g.,
+"registry.com/namespace/image"). Note that neither "name" nor "value" can
+include a tag or digest. Moreover, "name" must be a short name and hence
+cannot include a registry domain or refer to localhost.
+
+When pulling a short name, the configured aliases table will be used for
+resolving the short name. If a matching alias is found, it will be used
+without further consulting the unqualified-search registries list. If no
+matching alias is found, the behavior can be controlled via the
+`short-name-mode` option as described below.
+
+Note that tags and digests are stripped off a user-specified short name for
+alias resolution. Hence, "image", "image:tag" and "image@digest" all resolve
+to the same alias (i.e., "image"). Stripped off tags and digests are later
+appended to the resolved alias.
+
+Further note that drop-in configuration files (see containers-registries.conf.d(5))
+can override aliases in the specific loading order of the files. If the "value" of
+an alias is empty (i.e., ""), the alias will be erased. However, a given
+"name" may only be specified once in a single config file.
+
+
+#### Short-Name Aliasing: Modes
+
+The `short-name-mode` option supports three modes to control the behaviour of
+short-name resolution.
+
+* `enforcing`: If only one unqualified-search registry is set, use it as there
+ is no ambiguity. If there is more than one registry and the user program is
+ running in a terminal (i.e., stdout & stdin are a TTY), prompt the user to
+ select one of the specified search registries. If the program is not running
+ in a terminal, the ambiguity cannot be resolved which will lead to an error.
+
+* `permissive`: Behaves as enforcing but does not lead to an error if the
+ program is not running in a terminal. Instead, fallback to using all
+ unqualified-search registries.
+
+* `disabled`: Use all unqualified-search registries without prompting.
+
+If `short-name-mode` is not specified at all or left empty, default to the
+`permissive` mode. If the user-specified short name was not aliased already,
+the `enforcing` and `permissive` mode if prompted, will record a new alias
+after a successful pull. Note that the recorded alias will be written to
+`$XDG_CONFIG_HOME/containers/short-name-aliases.conf` to have a clear
+separation between possibly human-edited registries.conf files and the
+machine-generated `short-name-aliases-conf`. Note that `$HOME/.config` is used
+if `$XDG_CONFIG_HOME` is not set. If an alias is specified in a
+`registries.conf` file and also the machine-generated
+`short-name-aliases.conf`, the `short-name-aliases.conf` file has precedence.
+
 #### Normalization of docker.io references
 
 The Docker Hub `docker.io` is handled in a special way: every push and pull

go.mod

@@ -20,6 +20,7 @@ require (
  github.com/imdario/mergo v0.3.11
  github.com/klauspost/compress v1.11.2
  github.com/klauspost/pgzip v1.2.5
+ github.com/manifoldco/promptui v0.8.0
  github.com/morikuni/aec v1.0.0 // indirect
  github.com/mtrmac/gpgme v0.1.2
  github.com/opencontainers/go-digest v1.0.0

go.sum

@@ -24,6 +24,10 @@ github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6r
 github.com/blang/semver v3.1.0+incompatible/go.mod h1:kRBLl5iJ+tD4TcOOxsy/0fnwebNt5EWlYSAyrTnjyyk=
 github.com/checkpoint-restore/go-criu/v4 v4.0.2/go.mod h1:xUQBLp4RLc5zJtWY++yjOoMoB5lihDt7fai+75m+rGw=
 github.com/checkpoint-restore/go-criu/v4 v4.1.0/go.mod h1:xUQBLp4RLc5zJtWY++yjOoMoB5lihDt7fai+75m+rGw=
+github.com/chzyer/logex v1.1.10/go.mod h1:+Ywpsq7O8HXn0nuIou7OrIPyXbp3wmkHB+jjWRnGsAI=
+github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e h1:fY5BOSpyZCqRo5OhCuC+XN+r/bBCmeuuJtjz+bCNIf8=
+github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=
+github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMnBNeIyt5eFwwo7qiLfzFZmjNmxjkiQlU=
 github.com/cilium/ebpf v0.0.0-20200507155900-a9f01edf17e3/go.mod h1:XT+cAw5wfvsodedcijoh1l9cf7v1x9FlFB/3VmF/O8s=
 github.com/cilium/ebpf v0.0.0-20200702112145-1c8d4c9ef775/go.mod h1:7cR51M8ViRLIdUjrmSXlK9pkrsDlLHbO8jiB8X8JnOc=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
@@ -42,6 +46,8 @@ github.com/containerd/fifo v0.0.0-20190226154929-a9fb20d87448/go.mod h1:ODA38xgv
 github.com/containerd/go-runc v0.0.0-20180907222934-5a6d9f37cfa3/go.mod h1:IV7qH3hrUgRmyYrtgEeGWJfWbgcHL9CSRruz2Vqcph0=
 github.com/containerd/ttrpc v0.0.0-20190828154514-0e0f228740de/go.mod h1:PvCDdDGpgqzQIzDW1TphrGLssLDZp2GuS+X5DkEJB8o=
 github.com/containerd/typeurl v0.0.0-20180627222232-a93fcdb778cd/go.mod h1:Cm3kwCdlkCfMSHURc+r6fwoGH6/F1hH3S4sg0rLFWPc=
+github.com/containers/image v1.5.1 h1:ssEuj1c24uJvdMkUa2IrawuEFZBP12p6WzrjNBTQxE0=
+github.com/containers/image v3.0.2+incompatible h1:B1lqAE8MUPCrsBLE86J0gnXleeRq8zJnQryhiiGQNyE=
 github.com/containers/libtrust v0.0.0-20190913040956-14b96171aa3b h1:Q8ePgVfHDplZ7U33NwHZkrVELsZP5fYj9pM5WBZB2GE=
 github.com/containers/libtrust v0.0.0-20190913040956-14b96171aa3b/go.mod h1:9rfv8iPl1ZP7aqh9YA68wnZv2NUDbXdcdPHVz0pFbPY=
 github.com/containers/ocicrypt v1.0.1 h1:EToign46OSLTFWnb2oNj9RG3XDnkOX8r28ZIXUuk5Pc=
@@ -161,6 +167,8 @@ github.com/imdario/mergo v0.3.11 h1:3tnifQM4i+fbajXKBHXWEH+KvNHqojZ778UH75j3bGA=
 github.com/imdario/mergo v0.3.11/go.mod h1:jmQim1M+e3UYxmgPu/WyfjB3N3VflVyUjjjwH0dnCYA=
 github.com/json-iterator/go v1.1.6/go.mod h1:+SdeFBvtyEkXs7REEP0seUULqWtbJapLOCVDaaPEHmU=
 github.com/json-iterator/go v1.1.7/go.mod h1:KdQUCv79m/52Kvf8AW2vK1V8akMuk1QjK/uOdHXbAo4=
+github.com/juju/ansiterm v0.0.0-20180109212912-720a0952cc2a h1:FaWFmfWdAUKbSCtOU2QjDaorUexogfaMgbipgYATUMU=
+github.com/juju/ansiterm v0.0.0-20180109212912-720a0952cc2a/go.mod h1:UJSiEoRfvx3hP73CvoARgeLjaIOjybY9vj8PUPPFGeU=
 github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7VTCxuUUipMqKk8s4w=
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
 github.com/kisielk/errcheck v1.2.0/go.mod h1:/BMXB+zMLi60iA8Vv6Ksmxu/1UDYcXs4uQLJ+jE2L00=
@@ -205,6 +213,14 @@ github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORN
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/lunixbochs/vtclean v0.0.0-20180621232353-2d01aacdc34a h1:weJVJJRzAJBFRlAiJQROKQs8oC9vOxvm4rZmBBk0ONw=
+github.com/lunixbochs/vtclean v0.0.0-20180621232353-2d01aacdc34a/go.mod h1:pHhQNgMf3btfWnGBVipUOjRYhoOsdGqdm/+2c2E2WMI=
+github.com/manifoldco/promptui v0.8.0 h1:R95mMF+McvXZQ7j1g8ucVZE1gLP3Sv6j9vlF9kyRqQo=
+github.com/manifoldco/promptui v0.8.0/go.mod h1:n4zTdgP0vr0S3w7/O/g98U+e0gwLScEXGwov2nIKuGQ=
+github.com/mattn/go-colorable v0.0.9 h1:UVL0vNpWh04HeJXV0KLcaT7r06gOH2l4OW6ddYRUIY4=
+github.com/mattn/go-colorable v0.0.9/go.mod h1:9vuHe8Xs5qXnSaW/c/ABM9alt+Vo+STaOChaDxuIBZU=
+github.com/mattn/go-isatty v0.0.4 h1:bnP0vzxcAdeI1zdubAl5PjU6zsERjGZb7raWodagDYs=
+github.com/mattn/go-isatty v0.0.4/go.mod h1:M+lRXTBqGeGNdLjl/ufCoiOlB5xdOkqRJdNxMWT7Zi4=
 github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHXY=
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/mattn/go-runewidth v0.0.9 h1:Lm995f3rfxdpd6TSmuVCHVb/QhupuXlYr8sCI/QdE+0=
@@ -404,6 +420,7 @@ golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=