ProFTPD module mod_rlimit



The mod_rlimit module handles setting and enforcement of resource limits such as CPU, memory, and file descriptor usage.

By default, the mod_rlimit module will impose one resource restriction on new session processes: the RLIMIT_NPROC (see getrlimit(2) limit, which controls the number of processes which can be forked from this process, is set to zero. There is absolutely no reason for a proftpd session process to need to create a new process via fork(2).

This module is contained in the mod_rlimit.c file for ProFTPD 1.3.x, and is compiled by default. See the installation section for more details.

The most current version of mod_rlimit can be found in the ProFTPD source distribution:

  http://www.proftpd.org/

Directives


RLimitChroot

Syntax: RLimitChroot on|off
Default: on
Context: "server config", <VirtualHost>, <Global>
Module: mod_rlimit
Compatibility: 1.3.5rc5

The RLimitChroot directive is used to enable/disable checks for modifications to "sensitive" directories when a session is chrooted. These checks are designed to mitigate and guard against attacks such as the "Roaring Beast" attack; see:

When a session is chrooted, e.g. via the DefaultRoot directive or by <Anonymous> login, the checks for the "sensitive" directories are automatically enabled. To disable these checks, use:

  RLimitChroot off
Note: We strongly recommend that you do not disable these checks.

The checks in question will specifically prevent any attempts to upload files into the /etc and /lib directories, or attempts to delete, create, rename, link, or otherwise try to change anything in these directories. All attempts to make modifications will be rejected with "Permission denied" errors. In addition, the following message will be logged (at debug level 2):

  WARNING: attempt to use sensitive path '/etc/file' within chroot '/home/user', rejecting

The RLimitChroot directive is not intended to prevent "Roaring Beast" style attacks entirely; the guarded /etc and /lib directories might be created via other means, outside of ProFTPD, which would also allow for the attack. The RLimitChroot directive is meant to mitigate (not prevent) the attacks by making sure it cannot be done using just ProFTPD.


RLimitCPU

Syntax: RLimitCPU [scope] soft-limit|"max" [hard-limit|"max"]
Default: System defaults
Context: "server config", <VirtualHost>, <Global>
Module: mod_rlimit
Compatibility: 1.3.5rc2

The RLimitCPU directive is used to set a limit on the CPU usage, expressed as a maximum number of seconds.

RLimitCPU takes from one to three parameters. The first parameter is an optional scope parameter, indicating the scope of the resource limit. The scope parameter may be one of:

If none of these keywords are used, the resource limit is assumed to apply to both daemon and session processes.

The next parameters indicate the actual resource limits, both the so-called "soft limit" and any "hard limit". These parameters may be a number (indicating the number of seconds), or the value "max" to indicate that maximum resource limit value allowed is to be used.

Example:

  # Limit a given session to 30 minutes of CPU time (which can take
  # considerably longer than 30 minutes of wall time, due to CPU scheduling)
  RLimitCPU 1800


RLimitMemory

Syntax: RLimitMemory [scope] soft-limit|"max" [hard-limit|"max"]
Default: System defaults
Context: "server config", <VirtualHost>, <Global>
Module: mod_rlimit
Compatibility: 1.3.5rc2

The RLimitMemory directive is used to set a limit on the memory usage, expressed as a maximum number of bytes.

RLimitMemory takes from one to three parameters. The first parameter is an optional scope parameter, indicating the scope of the resource limit. The scope parameter may be one of:

If none of these keywords are used, the resource limit is assumed to apply to both daemon and session processes.

The next parameters indicate the actual resource limits, both the so-called "soft limit" and any "hard limit". These parameters may be a number (indicating the number of bytes), or the value "max" to indicate that maximum resource limit value allowed is to be used.

Example:

  # Limit a given session to 128MB minutes of memory
  RLimitMemory 128MB


RLimitOpenFiles

Syntax: RLimitOpenFiles [scope] soft-limit|"max" [hard-limit|"max"]
Default: System defaults
Context: "server config", <VirtualHost>, <Global>
Module: mod_rlimit
Compatibility: 1.3.5rc2

The RLimitOpenFiles directive is used to set a limit on the file descriptors, expressed as counts.

RLimitOpenFiles takes from one to three parameters. The first parameter is an optional scope parameter, indicating the scope of the resource limit. The scope parameter may be one of:

If none of these keywords are used, the resource limit is assumed to apply to both daemon and session processes.

The next parameters indicate the actual resource limits, both the so-called "soft limit" and any "hard limit". These parameters may be a number, or the value "max" to indicate that maximum resource limit value allowed is to be used.

Example:

  # Limit a given session to 12 open file descriptors
  RLimitMemory session 12


Installation

The mod_rlimit module is compiled into proftpd by default.



Author: $Author: castaglia $
Last Updated: $Date: 2014-01-31 17:08:10 $


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