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The new SECBIT_EXEC_RESTRICT_FILE, SECBIT_EXEC_DENY_INTERACTIVE, and their *_LOCKED counterparts are designed to be set by processes setting up an execution environment, such as a user session, a container, or a security sandbox. Unlike other securebits, these ones can be set by unprivileged processes. Like seccomp filters or Landlock domains, the securebits are inherited across processes. When SECBIT_EXEC_RESTRICT_FILE is set, programs interpreting code should control executable resources according to execveat(2) + AT_EXECVE_CHECK (see previous commit). When SECBIT_EXEC_DENY_INTERACTIVE is set, a process should deny execution of user interactive commands (which excludes executable regular files). Being able to configure each of these securebits enables system administrators or owner of image containers to gradually validate the related changes and to identify potential issues (e.g. with interpreter or audit logs). It should be noted that unlike other security bits, the SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE bits are dedicated to user space willing to restrict itself. Because of that, they only make sense in the context of a trusted environment (e.g. sandbox, container, user session, full system) where the process changing its behavior (according to these bits) and all its parent processes are trusted. Otherwise, any parent process could just execute its own malicious code (interpreting a script or not), or even enforce a seccomp filter to mask these bits. Such a secure environment can be achieved with an appropriate access control (e.g. mount's noexec option, file access rights, LSM policy) and an enlighten ld.so checking that libraries are allowed for execution e.g., to protect against illegitimate use of LD_PRELOAD. Ptrace restrictions according to these securebits would not make sense because of the processes' trust assumption. Scripts may need some changes to deal with untrusted data (e.g. stdin, environment variables), but that is outside the scope of the kernel. See chromeOS's documentation about script execution control and the related threat model: https://www.chromium.org/chromium-os/developer-library/guides/security/noexec-shell-scripts/ Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Christian Brauner <brauner@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Paul Moore <paul@paul-moore.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Jeff Xu <jeffxu@chromium.org> Tested-by: Jeff Xu <jeffxu@chromium.org> Signed-off-by: Mickaël Salaün <mic@digikod.net> Link: https://lore.kernel.org/r/20241212174223.389435-3-mic@digikod.net Signed-off-by: Kees Cook <kees@kernel.org> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.