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Hacks From Pax: SELinux And Access Decisions
Pax Dickinson
Security Contexts
SELinux makes access decisions by checking the security context of the subject (a process, sometimes associated with a user) against the action attempted (e.g. a file read) and the security context of the targeted object (such as a file or network port). These contexts are divided into three parts: a user identity, a role, and a domain or type. In the current SELinux policy, access is not restricted based on user identities, so we'll focus on roles and domains in this article.
User Roles
On an SELinux system, unlike a standard Linux system, root has no special privileges inherent to the account. SELinux privileges are denoted by a user's role. A standard user is assigned a role of user_r, which gives no special privileges. System administrator accounts are assigned a role of staff_r, which permits what is known as a "role transition" to the sysadm_r role. The sysadm_r role is the equivalent of the root account on a non-SELinux system, it has unfettered access to the system.
A staff user transitions to the sysadm_r role by using the newrole command, as shown below.
newrole -r sysadm_r
The user is then prompted for his or her password, successful entry of which will result in transition to the new role. You can view your current role by issuing an id -Z command.
Domains and Types
Domains and types are synonyms, typically the term "domain" is used when referring to processes and the term "type" is used referring to files. Types are the primary method used by SELinux to make authorization decisions. The strict policy defines relatively few users and roles, but contains hundreds of types.
Types are assigned by the security policy based on the path of the file in question, and the policy also transitions processes into an appropriate domain based on the context of the executed file and the domain of the process executing the file.
For example, the Apache webserver executable file has a type of httpd_exec_t. When that file is executed by the init process at bootup, the policy forces the new process to transition into the httpd_t domain. The httpd_t domain has the ability to read web content denoted by the httpd_content_t type, but not to change it or access any other domains not required for proper webserver operation.
You can view the type of a given file by using the -Z option of ls, and you can view the domain a process is running in by using the -Z option of ps. These -Z options are specific to SELinux and will not function on a non-SELinux system.
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Thank you for reading the LinuxSecurity.com weekly security newsletter. The purpose of this document is to provide our readers with a quick summary of each week's most relevant Linux security headline.
| Debian | ||
| Debian: New lynx packages fix arbitrary code execution | ||
| 27th, October, 2005
Updated package. advisories/debian/debian-new-lynx-packages-fix-arbitrary-code-execution |
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| Debian: New OpenSSL packages fix cryptographic weakness | ||
| 27th, October, 2005
Updated package. advisories/debian/debian-new-openssl-packages-fix-cryptographic-weakness-46955 |
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| Debian: New lynx-ssl packages fix arbitrary code execution | ||
| 27th, October, 2005
Updated package. advisories/debian/debian-new-lynx-ssl-packages-fix-arbitrary-code-execution |
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| Debian: New gnump3d packages fix several vulnerabilities | ||
| 28th, October, 2005
Updated package. advisories/debian/debian-new-gnump3d-packages-fix-several-vulnerabilities-33828 |
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| Debian: New netpbm-free packages fix arbitrary code execution | ||
| 28th, October, 2005
Updated package. advisories/debian/debian-new-netpbm-free-packages-fix-arbitrary-code-execution |
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| Debian: New gallery packages fix privilege escalation | ||
| 2nd, November, 2005
Updated profile. advisories/debian/debian-new-gallery-packages-fix-privilege-escalation |
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| Debian: New phpmyadmin packages fix several vulnerabilities | ||
| 2nd, November, 2005
Updated profile. advisories/debian/debian-new-phpmyadmin-packages-fix-several-vulnerabilities-72435 |
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| Gentoo | ||
| Gentoo: SELinux PAM Local password guessing attack | ||
| 28th, October, 2005
A vulnerability in the SELinux version of PAM allows a local attacker to brute-force system passwords. |
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| Gentoo: TikiWiki XSS vulnerability | ||
| 28th, October, 2005
TikiWiki is vulnerable to cross-site scripting attacks. |
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| Gentoo: Mantis Multiple vulnerabilities | ||
| 28th, October, 2005
Mantis is affected by multiple vulnerabilities ranging from information disclosure to arbitrary script execution. |
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| Gentoo: Ethereal Multiple vulnerabilities in protocol dissectors | ||
| 30th, October, 2005
Ethereal is vulnerable to numerous vulnerabilities, potentially resulting in the execution of arbitrary code or abnormal termination. |
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| Gentoo: XLI, Xloadimage Buffer overflow | ||
| 30th, October, 2005
XLI and Xloadimage contain a vulnerability which could potentially result in the execution of arbitrary code. |
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| Gentoo: libgda Format string vulnerabilities | ||
| 2nd, November, 2005
Two format string vulnerabilities in libgda may lead to the execution of arbitrary code. |
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| Gentoo: QDBM, ImageMagick, GDAL RUNPATH issues | ||
| 2nd, November, 2005
Multiple packages suffer from RUNPATH issues that may allow users in the "portage" group to escalate privileges. |
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| Red Hat | ||
| RedHat: Important: kernel security update | ||
| 27th, October, 2005
Updated kernel packages that fix several security issues and a page attribute mapping bug are now available for Red Hat Enterprise Linux 4. This update has been rated as having important security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-important-kernel-security-update-85756 |
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| RedHat: Moderate: curl security update | ||
| 2nd, November, 2005
Updated curl packages that fix a security issue are now available. This update has been rated as having moderate security impact by the Red Hat Security Response Team. |
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| RedHat: Important: wget security update | ||
| 2nd, November, 2005
Updated wget packages that fix a security issue are now available. This update has been rated as having important security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-important-wget-security-update-RHSA-2005-812-00 |
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| RedHat: Important: openssl security update | ||
| 2nd, November, 2005
Updated OpenSSL packages that fix a remote denial of service vulnerability are now available for Red Hat Enterprise Linux 2.1 This update has been rated as having important security impact by the Red Hat Security Response Team. |
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| RedHat: Moderate: openssl096b security update | ||
| 2nd, November, 2005
Updated OpenSSL096b compatibility packages that fix a remote denial of service vulnerability are now available. This update has been rated as having moderate security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-moderate-openssl096b-security-update-RHSA-2005-830-00 |
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