git: ce1af6eb54a4 - stable/14 - capsicum.4: Add some more detail from the Capsicum paper

The branch stable/14 has been updated by emaste:

URL: https://cgit.FreeBSD.org/src/commit/?id=ce1af6eb54a423af66054e3775bc71bb09c96b41

commit ce1af6eb54a423af66054e3775bc71bb09c96b41
Author:     Ed Maste <emaste@FreeBSD.org>
AuthorDate: 2025-06-14 17:57:33 +0000
Commit:     Ed Maste <emaste@FreeBSD.org>
CommitDate: 2025-07-22 20:30:30 +0000

    capsicum.4: Add some more detail from the Capsicum paper
    
    Adapt some language from "Capsicum: practical capabilities for UNIX"
    https://www.cl.cam.ac.uk/research/security/capsicum/papers/2010usenix-security-capsicum-website.pdf
    
    Reviewed by:    markj
    Discussed with: rwatson
    Event:          Kitchener-Waterloo Hackathon 202506
    Sponsored by:   The FreeBSD Foundation
    Differential Revision: https://reviews.freebsd.org/D50855
    
    (cherry picked from commit c54534e60263954fac4db5ebb041ed4597df1195)
    (cherry picked from commit ce65ff203a4f7ce59c8782f87d90a657f7ccbc46)
---
 share/man/man4/capsicum.4 | 47 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/share/man/man4/capsicum.4 b/share/man/man4/capsicum.4
index 6aefae9d6df2..1de8e4531f4f 100644
--- a/share/man/man4/capsicum.4
+++ b/share/man/man4/capsicum.4
@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd June 5, 2025
+.Dd June 17, 2025
 .Dt CAPSICUM 4
 .Os
 .Sh NAME
@@ -37,6 +37,12 @@
 .Nm
 is a lightweight OS capability and sandbox framework implementing a hybrid
 capability system model.
+.Nm
+is designed to blend capabilities with UNIX.
+This approach achieves many of the benefits of least-privilege operation, while
+preserving existing UNIX APIs and performance, and presents application authors
+with an adoption path for capability-oriented design.
+.Pp
 Capabilities are unforgeable tokens of authority that can be delegated and must
 be presented to perform an action.
 .Nm
@@ -59,6 +65,34 @@ namespaces) is restricted; only explicitly delegated rights, referenced by
 memory mappings or file descriptors, may be used.
 Once set, the flag is inherited by future children processes, and may not be
 cleared.
+.Pp
+Access to system calls in capability mode is restricted: some system calls
+requiring global namespace access are unavailable, while others are
+constrained.
+For instance,
+.Xr sysctl 2
+can be used to query process-local information such as address space layout,
+but also to monitor a system’s network connections.
+.Xr sysctl 2
+is constrained by explicitly marking \(~~60 of over 15000 parameters as permitted
+in capability mode; all others are denied.
+.Pp
+The system calls which require constraints are
+.Xr sysctl 2 ,
+.Xr shm_open 2
+.Pq which is permitted to create anonymous memory objects but not named ones
+and the
+.Xr openat 2
+family of system calls.
+The
+.Xr openat 2
+calls already accept a file descriptor argument as the directory to perform the
+.Xr open 2 ,
+.Xr rename 2 ,
+etc. relative to; in capability mode the
+.Xr openat 2
+family of system calls are constrained so that they can only operate on
+objects “under” the provided file descriptor.
 .It capabilities
 Limit operations that can be called on file descriptors.
 For example, a file descriptor returned by
@@ -152,3 +186,14 @@ and
 .An Kris Kennaway Aq Mt kris@FreeBSD.org
 at Google, Inc., and
 .An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net .
+Portions of this manual page are drawn from
+.Rs
+.%A Robert N. M. Watson
+.%A Jonathan Anderson
+.%A Ben Laurie
+.%A Kris Kennaway
+.%T Capsicum: practical capabilities for UNIX
+.%J USENIX Security Symposium
+.%D August 2010
+.%O DOI: 10.5555/1929820.1929824
+.Re