xfs_scrub: use dynamic users when running as a systemd service

Five years ago, systemd introduced the DynamicUser directive that
allocates a new unique user/group id, runs a service with those ids, and
deletes them after the service exits.  This is a good replacement for
User=nobody, since it eliminates the threat of nobody-services messing
with each other.

Make this transition ahead of all the other security tightenings that
will land in the next few patches, and add credits for the people who
suggested the change and reviewed it.

Link: https://0pointer.net/blog/dynamic-users-with-systemd.html
Suggested-by: Helle Vaanzinn <glitsj16@riseup.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

diff --git a/scrub/xfs_scrub@.service.in b/scrub/xfs_scrub@.service.in
index 855fe4de4dcfa10abca372484d518824b9682505..52068add834d8590ccf57734fb6f2666cfd99a81 100644 (file)
--- a/scrub/xfs_scrub@.service.in
+++ b/scrub/xfs_scrub@.service.in
@@ -17,7 +17,6 @@ ProtectHome=read-only
 PrivateTmp=no
 AmbientCapabilities=CAP_SYS_ADMIN CAP_FOWNER CAP_DAC_OVERRIDE CAP_DAC_READ_SEARCH CAP_SYS_RAWIO
 NoNewPrivileges=yes
-User=nobody
 Environment=SERVICE_MODE=1
 ExecStart=@sbindir@/xfs_scrub @scrub_args@ %f
 SyslogIdentifier=%N
@@ -31,3 +30,6 @@ Nice=19
 # Create the service underneath the scrub background service slice so that we
 # can control resource usage.
 Slice=system-xfs_scrub.slice
+
+# Dynamically create a user that isn't root
+DynamicUser=true