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Full Discussion: importance of '/dev' directory
Top Forums UNIX for Dummies Questions & Answers importance of '/dev' directory Post 538 by Neo on Wednesday 13th of December 2000 02:09:42 AM
Old 12-13-2000
The /dev directory is where the user interface to kernel device drivers and other <em> special files </em> are located. The UNIX kernel interface to devices such as modems, printers, disks happens using device drivers built into the kernel. User processes typically access devices (kernel device drivers) via special files. Many of the files are located in the /dev/ directory.

You ask, can someone gain root access via these files. To answer that we should define what root access means:


The UNIX <B> superuser </B> is a user with UID (user ID) 0 (zero) that are granted special privileges by the UNIX kernel. The login name for this user is normally "root" (it does not have to be). When a device file is called by a process and the process was run by the superuser, then the behavior of the device driver has special privileges. So, if a device driver had malicious code or a logic flaw that compromises the integrity of the system, the system can be compromised.

On many UNIX platforms, RAM is also managed via a special file, for example /dev/kmem (or something to that effect). A system vulnerability exists when this special file is world readable because clever people could read the system memory at any time. Reading system memory can compromise any system, not only UNIX but all systems.

The bottom line is that all files should have the proper permissions. Any file which runs as UID 0 has the potential for misuse. Remember the Stoll story about the C Egg? One of the methods used by the hackers was crontab files that are executed by the superuser process. When the root crontab file was found world writable, any process that is executed by the cron will execute as the superuser. Naturally, it is a very poor configuration management to leave these crontab files world-writable.

Files in the /dev directory can be the source of security breaches. Not all files are created nor executed equal. There are also files with permission that say 'set the UID of the calling user to 0' (SUID). When this flag is set, a file which is not owned by UID 0 gets the same privileges as the UID 0 user. All SUID 0 files require special precautions.
 

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LEARN ABOUT DEBIAN

list_devices

list_devices(1) 														   list_devices(1)

NAME

       list_devices - list allocatable devices

SYNOPSIS

       list_devices [-s] [ -U uid] -l [device]

       list_devices [-s] [ -U uid] -n [device]

       list_devices [-s] [ -U uid] -u [device]

       The list_devices utility lists the allocatable devices in the system according to specified qualifications.

       The  device  and all device special files associated with the device are listed. The device argument is optional and, if it is not present,
       all relevant devices are listed.

       The following options are supported:

       -l [device]     Lists the pathname(s) of the device special files associated with the device that are allocatable to the  current  process.
		       If device is given, lists only the files associated with the specified device.

       -n [device]     Lists  the  pathname(s)	of device special files associated with the device that are allocatable to the current process but
		       are not currently allocated. If device is given, lists only the files associated with that device.

       -s	       Silent. Suppresses any diagnostic output.

       -u [device]     Lists the pathname(s) of device special files, associated with the device that are allocated to the owner  of  the  current
		       process. If device is given, list only the files associated with that device.

       -U uid	       Uses the user ID uid instead of the real user ID of the current process when performing the list_devices operation.  Only a
		       user with the solaris.device.revoke authorization can use this option.

       The following exit values are returned:

       non--zero       An error occurred.

       /etc/security/device_allocate

       /etc/security/device_maps

       /etc/security/dev/*

       /usr/security/lib/*

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

       allocate(1), deallocate(1), bsmconv(1M), dminfo(1M), mkdevalloc(1M), mkdevmaps(1M), device_allocate(4), device_maps(4), attributes(5)

       The functionality described in this man page is available only if the Basic Security Module (BSM) has been  enabled.  See  bsmconv(1M)  for
       more information.

       /etc/security/dev, mkdevalloc(1M), and mkdevmaps(1M) might not be supported in a future release of the Solaris Operating Environment.

								    28 Mar 2005 						   list_devices(1)
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