Add support for --userns=nomap

From a security point of view, it would be nice to be able to map a
rootless usernamespace that does not use your own UID within the
container.

This would add protection against a hostile process escapping the
container and reading content in your homedir.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

3 files changed, 42 insertions, 4 deletions

diff --git a/docs/source/markdown/podman-create.1.md b/docs/source/markdown/podman-create.1.md
index f6d028f4d..ea31428fd 100644
--- a/docs/source/markdown/podman-create.1.md
+++ b/docs/source/markdown/podman-create.1.md
@@ -1225,6 +1225,15 @@ Without this argument the command will be run as root in the container.
 
 Set the user namespace mode for the container. It defaults to the **PODMAN_USERNS** environment variable. An empty value ("") means user namespaces are disabled unless an explicit mapping is set with the **--uidmap** and **--gidmap** options.
 
+Rootless user --userns=Key mappings:
+
+Key       | Host User |  Container User
+----------|---------------|---------------------
+""        |$UID           |0 (Default User account mapped to root user in container.)
+keep-id   |$UID           |$UID (Map user account to same UID within container.)
+auto      |$UID           | nil (Host User UID is not mapped into container.)
+nomap     |$UID           | nil (Host User UID is not mapped into container.)
+
 Valid _mode_ values are:
 
 **auto**[:_OPTIONS,..._]: automatically create a unique user namespace.
@@ -1247,6 +1256,8 @@ Podman allocates unique ranges of UIDs and GIDs from the `containers` subordinat
 
 **keep-id**: creates a user namespace where the current rootless user's UID:GID are mapped to the same values in the container. This option is ignored for containers created by the root user.
 
+**nomap**: creates a user namespace where the current rootless user's UID:GID are not mapped into the container. This option is ignored for containers created by the root user.
+
 **ns:**_namespace_: run the container in the given existing user namespace.
 
 **private**: create a new namespace for the container.
diff --git a/docs/source/markdown/podman-pod-create.1.md b/docs/source/markdown/podman-pod-create.1.md
index 1bf14efdb..f24458dc6 100644
--- a/docs/source/markdown/podman-pod-create.1.md
+++ b/docs/source/markdown/podman-pod-create.1.md
@@ -308,14 +308,30 @@ several times to map different ranges.
 
 Set the user namespace mode for all the containers in a pod. It defaults to the **PODMAN_USERNS** environment variable. An empty value ("") means user namespaces are disabled.
 
+Rootless user --userns=Key mappings:
+
+Key       | Host User |  Container User
+----------|---------------|---------------------
+""        |$UID           |0 (Default User account mapped to root user in container.)
+keep-id   |$UID           |$UID (Map user account to same UID within container.)
+auto      |$UID           | nil (Host User UID is not mapped into container.)
+nomap     |$UID           | nil (Host User UID is not mapped into container.)
+
 Valid _mode_ values are:
 
-- *auto[:*_OPTIONS,..._*]*: automatically create a namespace. It is possible to specify these options to `auto`:
+  - *auto[:*_OPTIONS,..._*]*: automatically create a namespace. It is possible to specify these options to `auto`:
+
   - *gidmapping=*_CONTAINER_GID:HOST_GID:SIZE_ to force a GID mapping to be present in the user namespace.
+
   - *size=*_SIZE_: to specify an explicit size for the automatic user namespace. e.g. `--userns=auto:size=8192`. If `size` is not specified, `auto` will estimate a size for the user namespace.
+
   - *uidmapping=*_CONTAINER_UID:HOST_UID:SIZE_ to force a UID mapping to be present in the user namespace.
-- *host*: run in the user namespace of the caller. The processes running in the container will have the same privileges on the host as any other process launched by the calling user (default).
-- *keep-id*: creates a user namespace where the current rootless user's UID:GID are mapped to the same values in the container. This option is ignored for containers created by the root user.
+
+  - *host*: run in the user namespace of the caller. The processes running in the container will have the same privileges on the host as any other process launched by the calling user (default).
+
+  - *keep-id*: creates a user namespace where the current rootless user's UID:GID are mapped to the same values in the container. This option is ignored for containers created by the root user.
+
+  - *nomap*: creates a user namespace where the current rootless user's UID:GID are not mapped into the container. This option is ignored for containers created by the root user.
 
 #### **--volume**, **-v**[=*[[SOURCE-VOLUME|HOST-DIR:]CONTAINER-DIR[:OPTIONS]]*]
 
diff --git a/docs/source/markdown/podman-run.1.md b/docs/source/markdown/podman-run.1.md
index 8f72d4f49..52143c934 100644
--- a/docs/source/markdown/podman-run.1.md
+++ b/docs/source/markdown/podman-run.1.md
@@ -1290,6 +1290,15 @@ When a user namespace is not in use, the UID and GID used within the container a
 
 Set the user namespace mode for the container. It defaults to the **PODMAN_USERNS** environment variable. An empty value ("") means user namespaces are disabled unless an explicit mapping is set with the **--uidmap** and **--gidmap** options.
 
+Rootless user --userns=Key mappings:
+
+Key       | Host User |  Container User
+----------|---------------|---------------------
+""        |$UID           |0 (Default User account mapped to root user in container.)
+keep-id   |$UID           |$UID (Map user account to same UID within container.)
+auto      |$UID           | nil (Host User UID is not mapped into container.)
+nomap     |$UID           | nil (Host User UID is not mapped into container.)
+
 Valid _mode_ values are:
 
 **auto**[:_OPTIONS,..._]: automatically create a unique user namespace.
@@ -1299,6 +1308,7 @@ The `--userns=auto` flag, requires that the user name `containers` and a range o
 Example: `containers:2147483647:2147483648`.
 
 Podman allocates unique ranges of UIDs and GIDs from the `containers` subordinate user ids. The size of the ranges is based on the number of UIDs required in the image. The number of UIDs and GIDs can be overridden with the `size` option.
+
 The rootless option `--userns=keep-id` uses all the subuids and subgids of the user. Using `--userns=auto` when starting new containers will not work as long as any containers exist that were started with `--userns=keep-id`.
 
   Valid `auto` options:
@@ -1313,10 +1323,11 @@ The rootless option `--userns=keep-id` uses all the subuids and subgids of the u
 
 **keep-id**: creates a user namespace where the current rootless user's UID:GID are mapped to the same values in the container. This option is ignored for containers created by the root user.
 
+**nomap**: creates a user namespace where the current rootless user's UID:GID are not mapped into the container. This option is ignored for containers created by the root user.
+
 **ns:**_namespace_: run the container in the given existing user namespace.
 
 **private**: create a new namespace for the container.
-
 This option is incompatible with **--gidmap**, **--uidmap**, **--subuidname** and **--subgidname**.
 
 #### **--uts**=*mode*