Bug #7879: File.readable? fails when ruby runs as root

• Status: Rejected
• Assignee: nobu (Nobuyoshi Nakada)
• Target version: 2.1.0
• ruby -v: ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-linux]

[balbi (Feliple Balbi)]

I have the following script to find sysfs (linux) files which are readable but throw an exception when read:

Dir.glob("/sys/**/*").each do |file|
next if File.directory?(file)

    if File.world_writable?(file)
            puts "#{file} is world-writable"
    end

    if File.readable?(file)
            begin
                    File.open(file) { |f|
                            result = f.readline
                    }
            rescue EOFError
                    nil
            rescue => e
                    puts e.message
            end
    end

end

If I run as a normal user, it works just fine, but when I run as root, even for files which are write only (chmod 200), File.readable?(f) will return true which makes my script fail. I have also tried File.readable_real? but it has the same outcome.

[ko1 (Koichi Sasada)]

• Category set to core
• Assignee set to nobu (Nobuyoshi Nakada)
• Target version set to 2.1.0

[kosaki (Motohiro KOSAKI)]

• Status changed from Open to Rejected

When run as root, access(2) ignore permission and always return success. That's UNIX filesystem semantics.
In the other words, this is completely your script bug.

You need specific concern when opening /proc, /sys and similar pseudo filesystem's file.

[mame (Yusuke Endoh)]

kosaki (Motohiro KOSAKI) wrote:

When run as root, access(2) ignore permission and always return success. That's UNIX filesystem semantics.
In the other words, this is completely your script bug.

Wow...

You need specific concern when opening /proc, /sys and similar pseudo filesystem's file.

Out of curiosity, what should we concern concretely? Should we assume File.readable? as a hint?

--
Yusuke Endoh [e-mail]

[kosaki (Motohiro KOSAKI)]

You need specific concern when opening /proc, /sys and similar pseudo filesystem's file.

Out of curiosity, what should we concern concretely? Should we assume File.readable? as a hint?

Pseudo filesystem hae several exceptional rule. this is one of them.
So, yes, when you can touch pseudo filesystems, I don't recommend to
use File.readable?. This is OS limitation and we can not fix them.