repoentitlement: check for kernels when disabling with --purge

If a kernel package is part of the removal and we cannot detect any other
Ubuntu kernel, block the operation. Otherwise, prompt the user.

Signed-off-by: Renan Rodrigo <[email protected]>

uaclient/entitlements/repo.py

@@ -25,6 +25,8 @@
 event = event_logger.get_event_logger()
 LOG = logging.getLogger(util.replace_top_level_logger_name(__name__))
 
+RE_KERNEL_PKG = r"^linux-image-[\d]+[.-][\d]+[.-][\d]+-[\d]+-[A-Za-z0-9_-]+$"
+
 
 class RepoEntitlement(base.UAEntitlement):
     repo_list_file_tmpl = "/etc/apt/sources.list.d/ubuntu-{name}.list"
@@ -125,6 +127,10 @@ def _perform_disable(self, silent=False):
             repo_origin_packages = apt.get_installed_packages_by_origin(
                 self.origin
             )
+
+            if not self.purge_kernel_check(repo_origin_packages):
+                return False
+
             packages_to_reinstall = []
             packages_to_remove = []
             for package in repo_origin_packages:
@@ -153,6 +159,42 @@ def _perform_disable(self, silent=False):
             self.execute_purge(packages_to_remove, packages_to_reinstall)
         return True
 
+    def purge_kernel_check(self, package_list):
+        linux_image_versions = [
+            package.name[len("linux-image-") :]
+            for package in package_list
+            if re.match(RE_KERNEL_PKG, package.name)
+        ]
+        if linux_image_versions:
+            print(messages.PURGE_KERNEL_REMOVAL)
+            print(" ".join(linux_image_versions))
+
+            current_kernel = system.get_kernel_info().uname_release
+            if current_kernel in linux_image_versions:
+                print(
+                    messages.PURGE_CURRENT_KERNEL.format(
+                        kernel_version=current_kernel
+                    )
+                )
+
+            installed_kernels = system.get_installed_ubuntu_kernels()
+            alternative_kernels = [
+                version
+                for version in installed_kernels
+                if version not in linux_image_versions
+            ]
+
+            if not alternative_kernels:
+                print(messages.PURGE_NO_ALTERNATIVE_KERNEL)
+                return False
+
+            if not util.prompt_for_confirmation(
+                messages.PURGE_KERNEL_CONFIRMATION
+            ):
+                return False
+
+        return True
+
     def prompt_for_purge(self, packages_to_remove, packages_to_reinstall):
         prompt = False
         if packages_to_remove:

uaclient/messages/__init__.py

@@ -272,6 +272,24 @@ class TxtColor:
 APT_REMOVING_SOURCE_FILE = "Removing apt source file: {filename}"
 APT_REMOVING_PREFERENCES_FILE = "Removing apt preferences file: {filename}"
 
+# Kernel checks for Purge
+PURGE_KERNEL_REMOVAL = (
+    "Purging the fips packages would uninstall the following kernel(s):"
+)
+PURGE_CURRENT_KERNEL = "{kernel_version} is the current running kernel."
+PURGE_NO_ALTERNATIVE_KERNEL = """\
+No other valid Ubuntu kernel was found in the system.
+Removing the package would potentially make the system unbootable.
+Aborting.
+"""
+PURGE_KERNEL_CONFIRMATION = (
+    """\
+If you cannot guarantee that other kernels in this system are bootable and
+working properly, *do not proceed*. You may end up with an unbootable system.
+"""
+    + PROCEED_YES_NO
+)
+
 # These are for the retry-auto-attach functionality
 AUTO_ATTACH_RETRY_NOTICE = """\
 Failed to automatically attach to Ubuntu Pro services {num_attempts} time(s).

uaclient/system.py

@@ -1,4 +1,5 @@
 import datetime
+import glob
 import logging
 import os
 import pathlib
@@ -178,6 +179,38 @@ def get_kernel_info() -> KernelInfo:
         )
 
 
+# This only works if we are root (because of permissions to 'file' the kernels
+# in /boot), but can't assert_root here due to circular imports.
+def get_installed_ubuntu_kernels():
+    # cursed circular import
+    from uaclient.apt import get_installed_packages_names
+
+    linux_image = [
+        package
+        for package in get_installed_packages_names()
+        if "linux-image-" in package
+    ]
+    vmlinux_kernel_files = [
+        file
+        for file in glob.glob("/boot/vmlinu[x|z]-*")
+        if "Linux kernel" in subp(["file", file])[0]
+    ]
+
+    linux_image_versions = [
+        package_name[len("linux-image-") :] for package_name in linux_image
+    ]
+    vmlinuz_versions = [
+        file_name[len("/boot/vmlinux-") :]
+        for file_name in vmlinux_kernel_files
+    ]
+
+    return [
+        version
+        for version in vmlinuz_versions
+        if version in linux_image_versions
+    ]
+
+
 @lru_cache(maxsize=None)
 def get_dpkg_arch() -> str:
     out, _err = subp(["dpkg", "--print-architecture"])