Btrfs send receive + Samba, ERROR: lsetxattr security.selinux= failed. Operation not supported.

[Chris Murphy]

Short question: Is it possible to change a file's security labeling
while the underlying file system is mounted with -o context= ? Or is
that supposed to fail?


Explanation:

Two separate Btrfs file systems volumes mounted at
/brick0
/brick1

I used mount option -o context=system_u:object_r:samba_share_t:s0 and
they're both being used by Samba just fine without problems.

But then:

# btrfs subvolume snapshot -r /brick0/sam840ev\:chrishome\:20150403/
/brick0/sam840ev\:chrishome\:20150403-1/
# btrfs send /brick0/sam840ev\:chrishome\:20150403-1/ | btrfs receive /brick1
ERROR: lsetxattr .android
security.selinux=unconfined_u:object_r:unlabeled_t:s0 failed.
Operation not supported

The contents of this subvolume/snapshot I'm trying to send are from a
remote rsync -a copy from an HFS+ volume where there are no security
labels.

The problem doesn't happen if I unmount /brick1 and remount without -o
context= (and hence also Samba sharing isn't enabled either while the
send-receive is happening).

I filed a bug thinking it might be a btrfs bug, before I tried
remounting without this context. So the question is whether this ought
to work or not. It's a small problem in my case, but I could see the
inability to use btrfs send-receive between Samba mounted Btrfs
volumes or subvolumes to be a problem. Even if I mount a subvolume
with -o context, any subsequent subvolume for that same volume
inherits that context even if not specified.

https://bugzilla.kernel.org/show_bug.cgi?id=96121




-- 
Chris Murphy