Only try and set permissions if permissions have changed. (#295)

* Only try and set permissions if permissions have changed.

This is a workaround for jruby/jruby#6693 - stat
is currently reporting incorrect values of `uid` and `gid` on aarch64 linux
nodes, and appears to be setting `uid` and `gid` to 0, ie `root`

It is highly unlikely that `chown` needs to be called on the file - and even more unlikely
that `chown` would succeed anyway - `chmod` typically requires superuser privileges, unless
the change of ownerhip is a change of group to another group the user is already a member of.

This workaround updates the code to only attempt to call `chown` in the unlikely event that file ownership
of the temp file is different from the original file, which should avoid the scenario that is currently
occurring due to the above jruby bug. This commit also falls back to a non-atomic write in the event
of a failure to write the file atomically.

Author: robbavey

CHANGELOG.md

@@ -1,3 +1,10 @@
+## 4.3.1
+  - Add extra safety to `chown` call in `atomic_write`, avoiding plugin crashes and falling back to a 
+  `non_atomic_write` in the event of failure [#295](https://github.com/logstash-plugins/logstash-input-file/pull/295)
+  - Refactor: unify event updates to happen in one place [#297](https://github.com/logstash-plugins/logstash-input-file/pull/297)
+  - Test: Actually retry tests on `RSpec::Expectations::ExpectationNotMetError` and retry instead of relying on timeout
+  [#297](https://github.com/logstash-plugins/logstash-input-file/pull/297)
+
 ## 4.3.0
   - Add ECS Compatibility Mode [#291](https://github.com/logstash-plugins/logstash-input-file/pull/291)
 

lib/filewatch/helper.rb

@@ -30,15 +30,18 @@ def write_atomically(file_name)
     temp_file.binmode
     return_val = yield temp_file
     temp_file.close
+    new_stat = File.stat(temp_file)
 
     # Overwrite original file with temp file
     File.rename(temp_file.path, file_name)
 
     # Unable to get permissions of the original file => return
     return return_val if old_stat.nil?
 
-    # Set correct uid/gid on new file
-    File.chown(old_stat.uid, old_stat.gid, file_name) if old_stat
+    # Set correct uid/gid on new file if ownership is different.
+    if old_stat && (old_stat.gid != new_stat.gid || old_stat.uid != new_stat.uid)
+      File.chown(old_stat.uid, old_stat.gid, file_name) if old_stat
+    end
 
     return_val
   end

lib/filewatch/sincedb_collection.rb

@@ -225,13 +225,24 @@ def sincedb_write(time = Time.now)
 
     # @return expired keys
     def atomic_write(time)
-      FileHelper.write_atomically(@full_path) do |io|
-        @serializer.serialize(@sincedb, io, time.to_f)
+      logger.trace? && logger.trace("non_atomic_write: ", :time => time)
+      begin
+        FileHelper.write_atomically(@full_path) do |io|
+          @serializer.serialize(@sincedb, io, time.to_f)
+        end
+      rescue Errno::EPERM, Errno::EACCES => e
+        logger.warn("sincedb_write: unable to write atomically due to permissions error, falling back to non-atomic write: #{path} error:", :exception => e.class, :message => e.message)
+        @write_method = method(:non_atomic_write)
+        non_atomic_write(time)
+      rescue => e
+        logger.warn("sincedb_write: unable to write atomically, attempting non-atomic write: #{path} error:", :exception => e.class, :message => e.message)
+        non_atomic_write(time)
       end
     end
 
     # @return expired keys
     def non_atomic_write(time)
+      logger.trace? && logger.trace("non_atomic_write: ", :time => time)
       File.open(@full_path, "w+") do |io|
         @serializer.serialize(@sincedb, io, time.to_f)
       end

logstash-input-file.gemspec

@@ -1,7 +1,7 @@
 Gem::Specification.new do |s|
 
   s.name            = 'logstash-input-file'
-  s.version         = '4.3.0'
+  s.version         = '4.3.1'
   s.licenses        = ['Apache-2.0']
   s.summary         = "Streams events from files"
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program"