cache_store: handle corrupt DBM database.

When the DBM database cannot be read by the current version of Ruby's
DBM library (due to corruption or another incompatibility) it segfaults
or freezes which takes down the entire Homebrew Ruby process.

This isn't desirable so instead perform a shell out with the Homebrew
Ruby to see if it can read the DBM database before we try to use the
information. If this hangs or crashes: silently delete the database and
recreate it.

Library/Homebrew/cache_store.rb

@@ -1,5 +1,6 @@
 require "dbm"
 require "json"
+require "timeout"
 
 #
 # `CacheStoreDatabase` acts as an interface to a persistent storage mechanism
@@ -46,7 +47,7 @@ class CacheStoreDatabase
   #
   # @return [Boolean]
   def created?
-    File.exist?(cache_path)
+    cache_path.exist?
   end
 
   private
@@ -57,6 +58,10 @@ class CacheStoreDatabase
   #   https://docs.oracle.com/cd/E17276_01/html/api_reference/C/envopen.html
   DATABASE_MODE = 0664
 
+  # Spend 5 seconds trying to read the DBM file. If it takes longer than this it
+  # has likely hung or segfaulted.
+  DBM_TEST_READ_TIMEOUT = 5
+
   # Lazily loaded database in read/write mode. If this method is called, a
   # database file with be created in the `HOMEBREW_CACHE` with name
   # corresponding to the `@type` instance variable
@@ -66,6 +71,29 @@ class CacheStoreDatabase
     # DBM::WRCREAT: Creates the database if it does not already exist
     @db ||= begin
       HOMEBREW_CACHE.mkpath
+      if created?
+        dbm_test_read_cmd = SystemCommand.new(
+          ENV["HOMEBREW_RUBY_PATH"],
+          args: [
+            "-rdbm",
+            "-e",
+            "DBM.open('#{dbm_file_path}', #{DATABASE_MODE}, DBM::READER).size",
+          ],
+          print_stderr: false,
+          must_succeed: true,
+        )
+        dbm_test_read_success = begin
+          Timeout.timeout(DBM_TEST_READ_TIMEOUT) do
+            dbm_test_read_cmd.run!
+            true
+          end
+        rescue ErrorDuringExecution, Timeout::Error
+          odebug "Failed to read #{dbm_file_path}!"
+          Process.kill(:KILL, dbm_test_read_cmd.pid)
+          false
+        end
+        cache_path.delete unless dbm_test_read_success
+      end
       DBM.open(dbm_file_path, DATABASE_MODE, DBM::WRCREAT)
     end
   end
@@ -83,7 +111,7 @@ class CacheStoreDatabase
   #
   # @return [String]
   def dbm_file_path
-    File.join(HOMEBREW_CACHE, @type.to_s)
+    "#{HOMEBREW_CACHE}/#{@type}"
   end
 
   # The path where the database resides in the `HOMEBREW_CACHE` for the given
@@ -91,7 +119,7 @@ class CacheStoreDatabase
   #
   # @return [String]
   def cache_path
-    "#{dbm_file_path}.db"
+    Pathname("#{dbm_file_path}.db")
   end
 end
 

Library/Homebrew/system_command.rb

@@ -19,6 +19,8 @@ end
 class SystemCommand
   extend Predicable
 
+  attr_reader :pid
+
   def self.run(executable, **options)
     new(executable, **options).run!
   end
@@ -122,6 +124,7 @@ class SystemCommand
 
     raw_stdin, raw_stdout, raw_stderr, raw_wait_thr =
       Open3.popen3(env, [executable, executable], *args, **options)
+    @pid = raw_wait_thr.pid
 
     write_input_to(raw_stdin)
     raw_stdin.close_write
@@ -191,6 +194,7 @@ class SystemCommand
     end
 
     def success?
+      return false if @exit_status.nil?
       @exit_status.zero?
     end
 

Library/Homebrew/test/cache_store_spec.rb

@@ -118,15 +118,15 @@ describe CacheStoreDatabase do
   end
 
   describe "#created?" do
-    let(:cache_path) { "path/to/homebrew/cache/sample.db" }
+    let(:cache_path) { Pathname("path/to/homebrew/cache/sample.db") }
 
     before(:each) do
       allow(subject).to receive(:cache_path).and_return(cache_path)
     end
 
-    context "`File.exist?(cache_path)` returns `true`" do
+    context "`cache_path.exist?` returns `true`" do
       before(:each) do
-        allow(File).to receive(:exist?).with(cache_path).and_return(true)
+        allow(cache_path).to receive(:exist?).and_return(true)
       end
 
       it "returns `true`" do
@@ -134,9 +134,9 @@ describe CacheStoreDatabase do
       end
     end
 
-    context "`File.exist?(cache_path)` returns `false`" do
+    context "`cache_path.exist?` returns `false`" do
       before(:each) do
-        allow(File).to receive(:exist?).with(cache_path).and_return(false)
+        allow(cache_path).to receive(:exist?).and_return(false)
       end
 
       it "returns `false`" do

Library/Homebrew/utils/ruby.sh

@@ -47,7 +47,7 @@ setup-ruby-path() {
         then
           odie "Failed to install vendor Ruby."
         fi
-        rm -rf "$vendor_dir/bundle/ruby" "$HOMEBREW_CACHE/linkage.db"
+        rm -rf "$vendor_dir/bundle/ruby"
         HOMEBREW_RUBY_PATH="$vendor_ruby_path"
       fi
     fi