From e586edcb410543768ef009eaa22a2d9dd4a53846 Mon Sep 17 00:00:00 2001 From: Dr. David Alan Gilbert Date: Wed, 24 Feb 2021 19:56:25 +0000 Subject: virtiofs: drop remapped security.capability xattr as needed On Linux, the 'security.capability' xattr holds a set of capabilities that can change when an executable is run, giving a limited form of privilege escalation to those programs that the writer of the file deemed worthy. Any write causes the 'security.capability' xattr to be dropped, stopping anyone from gaining privilege by modifying a blessed file. Fuse relies on the daemon to do this dropping, and in turn the daemon relies on the host kernel to drop the xattr for it. However, with the addition of -o xattrmap, the xattr that the guest stores its capabilities in is now not the same as the one that the host kernel automatically clears. Where the mapping changes 'security.capability', explicitly clear the remapped name to preserve the same behaviour. This bug is assigned CVE-2021-20263. Signed-off-by: Dr. David Alan Gilbert Reviewed-by: Vivek Goyal --- docs/tools/virtiofsd.rst | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'docs') diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst index 866b7db3ee..00554c75bd 100644 --- a/docs/tools/virtiofsd.rst +++ b/docs/tools/virtiofsd.rst @@ -228,6 +228,10 @@ The 'map' type adds a number of separate rules to add **prepend** as a prefix to the matched **key** (or all attributes if **key** is empty). There may be at most one 'map' rule and it must be the last rule in the set. +Note: When the 'security.capability' xattr is remapped, the daemon has to do +extra work to remove it during many operations, which the host kernel normally +does itself. + xattr-mapping Examples ---------------------- -- cgit v1.2.3-55-g7522