Add an OS X startup item to set the permissions and/or ownership of the

BPF devices, and add a README.macosx file to explain how to install and
use that startup item.

1 files changed, 43 insertions, 0 deletions

diff --git a/README.macosx b/README.macosx
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index 00000000..25794d88
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+As with other systems using BPF, Mac OS X allows users with read access
+to the BPF devices to capture packets with libpcap and allows users with
+write access to the BPF devices to send packets with libpcap.
+
+On some systems that use BPF, the BPF devices live on the root file
+system, and the permissions and/or ownership on those devices can be
+changed to give users other than root permission to read or write those
+devices.
+
+On newer versions of FreeBSD, the BPF devices live on devfs, and devfs
+can be configured to set the permissions and/or ownership of those
+devices to give users other than root permission to read or write those
+devices.
+
+On Mac OS X, the BPF devices live on devfs, but the OS X version of
+devfs is based on an older (non-default) FreeBSD devfs, and that version
+of devfs cannot be configured to set the permissions and/or ownership of
+those devices.
+
+Therefore, we supply a "startup item" for OS X that will change the
+ownership of the BPF devices so that the "admin" group owns them, and
+will change the permission of the BPF devices to rw-rw----, so that all
+users in the "admin" group - i.e., all users with "Allow user to
+administer this computer" turned on - have both read and write access to
+them.
+
+The startup item is in the ChmodBPF directory in the source tree.  A
+/Library/StartupItems directory should be created if it doesn't already
+exist, and the ChmodBPF directory should be copied to the
+/Library/StartupItems directory (copy the entire directory, so that
+there's a /Library/StartupItems/ChmodBPF directory, containing all the
+files in the source tree's ChmodBPF directory; don't copy the individual
+items in that directory to /Library/StartupItems).
+
+If you want to give a particular user permission to access the BPF
+devices, rather than giving all administrative users permission to
+access them, you can have the ChmodBPF/ChmodBPF script change the
+ownership of /dev/bpf* without changing the permissions.  If you want to
+give a particular user permission to read and write the BPF devices and
+give the administrative users permission to read but not write the BPF
+devices, you can have the script change the owner to that user, the
+group to "admin", and the permissions to rw-r-----.  Other possibilities
+are left as an exercise for the reader.