On Mon, Feb 15, 2021 at 9:52 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Fri, Feb 12, 2021 at 10:30:13AM +0000, Luis Henriques wrote: > > Hi! > > > > I've recently executed the generic fstests on virtiofs and decided to have > > a closer look at generic/099 failure. In a nutshell, here's the sequence > > of commands that reproduce that failure: > > > > # umask 0 > > # mkdir acldir > > # chacl -b "u::rwx,g::rwx,o::rwx" "u::r-x,g::r--,o::---" acldir > > # touch acldir/file1 > > # umask 722 > > # touch acldir/file2 > > # ls -l acldir > > total 0 > > -r--r----- 1 root root 0 Feb 12 10:04 file1 > > ----r----- 1 root root 0 Feb 12 10:05 file2 > > > > The failure is that setting umask to 722 shouldn't affect the new file2 > > because acldir has a default ACL (from umask(2): "... if the parent > > directory has a default ACL (see acl(5)), the umask is ignored..."). > > > > So... I tried to have look at the code, and initially I thought that the > > problem was in (kernel) function fuse_create_open(), where we have this: > > > > if (!fm->fc->dont_mask) > > mode &= ~current_umask(); > > > > but then I went down the rabbit hole, into the user-space code, and > > couldn't reach a conclusion. Maybe the issue is that there's in fact no > > support for this POSIX ACLs in virtiofs/FUSE? Any ideas? > > Hi, > > [ CC Miklos and linux-fsdevel ] > > I debugged into this a little. There are many knobs and it is little > confusing that what are right set of fixes. > > So what's happening in this case is that fc->dont_mask is not set. That > means fuse client is modifying mode using umask. First time you > touch file, umask is 0, so there is no modification. But next time, > you set umask to 722, and fuse modifies mode before sending file > create request to server. virtiofs server is already running with > umask 0, so it does not touch the mode. > > So that means, that in case of default acl, fuse client should not > be modifying mode using umask. But question is when should fuse > skip applying umask. > > I see that fuse always sets SB_POSIXACL. That means VFS is not > going to apply umask and all the umask handling is with-in fuse. > > sb->s_flags |= SB_POSIXACL; > > Currently fuse sets fc->dont_mask in two conditions. > > - If the caller mounted with flag MS_POSIXACL, then fc->dont_mask is set. > - If fuse server opted in for option FUSE_DONT_MASK, then fc->dont_mask > is set. > > I see that for virtiofs, both the conditions are not true out of the > box. In fact looks like ACL support is not fully enabled, because > I don't see fuse server opting in for FUSE_POSIX_ACL. > > I suspect that we probably should provide an option in virtiofsd to > enable/disable acl support. Sounds good. > Setting FUSE_DONT_MASK is tricky. If we leave it to fuse, that means > fuse will have to query acl to figure out if default acl is set or > not on parent dir. And that data could be stale and there could be > races w.r.t setting acls from other client. > > If we do set FUSE_DONT_MASK, that means in file creation path virtiofsd > server will have to switch its umask to one provided in request. Given > its a per process property, we will have to have some locks to make > sure other create requests are not progressing in parallel. And that > hope host does the right thing. That is apply umask if parent dir does > not have default acl otherwise apply umask (as set by virtiofsd process). > > Miklos, does above sound reasonable. You might have more thoughts on > how to handle this best in fuse/virtiofs. fv_queue_worker() does unshare(CLONE_FS) for the fchdir() call in xattr ops, which means that umask is now a per-thread propery in virtiofsd. So setting umask before create ops sounds like a good solution. Thanks, Miklos > > Vivek >
