linux-kernel - Re: SYSFS "errors"

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 19 Feb 2013 10:42:55 -0300
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	balbi@...com, Greg KH <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, JBottomley@...allels.com,
	linux-scsi@...r.kernel.org, davem@...emloft.net,
	netdev@...r.kernel.org, Doug Thompson <dougthompson@...ssion.com>,
	linux-edac@...r.kernel.org, rjw@...k.pl, linux-pm@...r.kernel.org
Subject: Re: SYSFS "errors"

Em Tue, 19 Feb 2013 14:06:26 +0100
Borislav Petkov <bp@...en8.de> escreveu:

> > No, on both cases, open() will return an error (-ENOENT against -EPERM).
> 
> What if it is a shell script doing:
> 
> cat /sys/devices/system/edac/mc/mc0/sdram_scrub_rate
> 
> or similar?

Well, cat will return "1" if an error is found, no matter what error happened. 

With an existing file (-ENOSYS):

	$ cat /sys/devices/system/edac/mc/mc0/sdram_scrub_rate; echo $?

	cat: /sys/devices/system/edac/mc/mc0/sdram_scrub_rate: No such device
	1

When the file doesn't exist (-ENOENT):
	$ cat /sys/devices/system/edac/mc/mc0/sdram_scrub_rate_not_exist; echo $?
	cat: /sys/devices/system/edac/mc/mc0/sdram_scrub_rate_not_exist: No such file or directory
	1

When permission doesn't match (-EPERM):
	$ cat /sys/devices/system/cpu/probe; echo $?
	cat: /sys/devices/system/cpu/probe: Permission denied
	1

When everything is ok, it will return 0
	$ cat /sys/devices/system/edac/mc/mc0/ce_count; echo $? >/dev/null
	0

A script ready to handle -ENOSYS would be doing, instead:

	RATE=$(cat /sys/devices/system/edac/mc/mc0/ce_count 2>/dev/null)
	if [ "$?" == "0" ]; then echo "Scrub rate: $RATE"; fi

So, a bash script won't notice any difference.

The only difference will be noticed if the script is written on some other 
language and the script is dumb enough to assume success if the errno is
different than -ENOSYS.

-- 

Cheers,
Mauro
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/