From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752936AbaJFQAb (ORCPT ); Mon, 6 Oct 2014 12:00:31 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:38406 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751252AbaJFQA3 (ORCPT ); Mon, 6 Oct 2014 12:00:29 -0400 Date: Mon, 6 Oct 2014 16:00:06 +0000 From: Serge Hallyn To: "Eric W. Biederman" , Miklos Szeredi , Alexander Viro , fuse-devel , Kernel Mailing List , Linux-Fsdevel , "Serge E. Hallyn" Subject: Re: [PATCH v2 0/3] fuse: Add support for mounts from pid/user namespaces Message-ID: <20141006160006.GE26187@ubuntumail> References: <87wq8reftb.fsf@x220.int.ebiederm.org> <20140925184403.GB28101@ubuntu-hedt> <87bnq3a4xy.fsf@x220.int.ebiederm.org> <20140925194825.GB39447@ubuntu-hedt> <874mvtkfg2.fsf@x220.int.ebiederm.org> <20140927042447.GA19672@ubuntu-hedt> <87tx3qdxuz.fsf@x220.int.ebiederm.org> <20140930162559.GA1057@ubuntu-hedt> <20141005164821.GA5691@ubuntu-mba51> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141005164821.GA5691@ubuntu-mba51> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Seth Forshee (seth.forshee@canonical.com): ... > After digging into this some more I think I agree with you. At minimum > letting users insert arbitrary xattrs via fuse bypasses the usual > restrictions on setting xattrs. This is probably mitigated by the > limited visibility of the fuse mount in the usual case for unprivileged > users, but it does seem like a bad idea fundamentally. > > So I was thinking of something like the following (untested) to let root > in the host support privileged xattrs while limiting unprivileged users > to user.*. Miklos, does this look acceptable or would you prefer > something different? So it won't be possible to set capabilities in a fuse fs? This may be necessary, but it will prevent i.e. live-iso builders from writing for instance a CAP_NET_RAW=pe (instead of setuid-root) /bin/ping in the iso. > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c > index e3123bfbc711..1a3ee5663dea 100644 > --- a/fs/fuse/dir.c > +++ b/fs/fuse/dir.c > @@ -1882,6 +1882,10 @@ static int fuse_setxattr(struct dentry *entry, const char *name, > if (fc->no_setxattr) > return -EOPNOTSUPP; > > + if (!(fc->flags & FUSE_PRIV_XATTRS) && > + strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) != 0) > + return -EOPNOTSUPP; > + > req = fuse_get_req_nopages(fc); > if (IS_ERR(req)) > return PTR_ERR(req); > @@ -1925,6 +1929,10 @@ static ssize_t fuse_getxattr(struct dentry *entry, const char *name, > if (fc->no_getxattr) > return -EOPNOTSUPP; > > + if (!(fc->flags & FUSE_PRIV_XATTRS) && > + strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) != 0) > + return -EOPNOTSUPP; > + > req = fuse_get_req_nopages(fc); > if (IS_ERR(req)) > return PTR_ERR(req); > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 81187ba04e4a..bc0fd14b962a 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -46,6 +46,11 @@ > doing the mount will be allowed to access the filesystem */ > #define FUSE_ALLOW_OTHER (1 << 1) > > +/** If the FUSE_PRIV_XATTRS flag is given, then xattrs outside the > + user.* namespace are allowed. This option is only allowed for > + system root. */ > +#define FUSE_PRIV_XATTRS (1 << 2) > + > /** Number of page pointers embedded in fuse_req */ > #define FUSE_REQ_INLINE_PAGES 1 > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > index b88b5a780228..6716b56d43a1 100644 > --- a/fs/fuse/inode.c > +++ b/fs/fuse/inode.c > @@ -493,6 +493,7 @@ enum { > OPT_ALLOW_OTHER, > OPT_MAX_READ, > OPT_BLKSIZE, > + OPT_PRIV_XATTRS, > OPT_ERR > }; > > @@ -505,6 +506,7 @@ static const match_table_t tokens = { > {OPT_ALLOW_OTHER, "allow_other"}, > {OPT_MAX_READ, "max_read=%u"}, > {OPT_BLKSIZE, "blksize=%u"}, > + {OPT_PRIV_XATTRS, "priv_xattr"}, > {OPT_ERR, NULL} > }; > > @@ -592,6 +594,12 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev) > d->blksize = value; > break; > > + case OPT_PRIV_XATTRS: > + if (!capable(CAP_SYS_ADMIN)) > + return 0; > + d->flags |= FUSE_PRIV_XATTRS; > + break; > + > default: > return 0; > } >