extattr(9): Mention system namespace restrictions in a jail

Reported by:		netchild
Reviewed by:		gbe
Differential revision:	https://reviews.freebsd.org/D41676
MFC after:		1 week

share/man/man9/extattr.9

@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd December 23, 1999
+.Dd September 1, 2023
 .Dt EXTATTR 9
 .Os
 .Sh NAME
@@ -54,6 +54,10 @@ attribute data is protected according the normal discretionary
 and mandatory protections associated with the data in the file or
 directory; system attribute data is protected such that appropriate
 privilege is required to directly access or manipulate these attributes.
+By default processes in a
+.Xr jail 8
+can not access to the system attribute data unless allow.extattr
+configuration parameter is specified.
 .Pp
 Reads of extended attribute data may return specific contiguous regions of
 the meta-data, in the style of
@@ -77,6 +81,7 @@ Appropriate vnode extended attribute calls are:
 and
 .Xr VOP_SETEXTATTR 9 .
 .Sh SEE ALSO
+.Xr jail 8 ,
 .Xr VFS 9 ,
 .Xr VFS_EXTATTRCTL 9 ,
 .Xr VOP_GETEXTATTR 9 ,