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Violators will be prosecuted for from ; Fri, 2 Feb 2018 15:33:52 -0000 Subject: Re: [RFC PATCH v4 1/2] fuse: introduce new fs_type flag FS_IMA_NO_CACHE From: Mimi Zohar To: Miklos Szeredi , Christoph Hellwig Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alban Crequy , Miklos Szeredi , Alexander Viro , Dmitry Kasatkin , James Morris , "Serge E . Hallyn" , Seth Forshee , Dongsu Park , linux-kernel@vger.kernel.org Date: Fri, 02 Feb 2018 10:33:44 -0500 In-Reply-To: <1517584816.3171.61.camel@linux.vnet.ibm.com> References: <86832c6adb256f29f44b6229222b80964fc8cfcc.1517314847.git.dongsu@kinvolk.io> <1517584816.3171.61.camel@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Message-Id: <1517585624.3171.64.camel@linux.vnet.ibm.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, 2018-02-02 at 10:20 -0500, Mimi Zohar wrote: > Hi Miklos, > > On Tue, 2018-01-30 at 19:06 +0100, Dongsu Park wrote: > > From: Alban Crequy > > > > This new fs_type flag FS_IMA_NO_CACHE means files should be re-measured, > > re-appraised and re-audited each time. Cached integrity results should > > not be used. > > > > It is useful in FUSE because the userspace FUSE process can change the > > underlying files at any time without notifying the kernel. > > Both IMA-measurement and IMA-appraisal cache the integrity results and > are dependent on the kernel to detect when a file changes in order to > clear the cached info and force the file to be re-evaluated.  This > detection was dependent on i_version changing.  For filesystems that > do not support i_version, remote or fuse filesystems, where the kernel > does not detect the file change, the file was measured and the > signature evaluated just once. > > With commit a2a2c3c8580a ("ima: Use i_version only when filesystem > supports it"), which is being upstreamed in this open window, > i_version is considered an optimization.  If i_version is not enabled, > either because the local filesystem does not support it or the > filesystem wasn't mounted with i_version, the file will now always be > re-evaluated. > > That patch does not address FUSE or remote filesystems, as the kernel > does not detect the change.  Further, even if the kernel could detect > the change, FUSE filesystems by definition are untrusted. > > The original patches addressed FUSE filesystems, by defining a new IMA > policy option, forcing the file to be re-evaluated based on the > filesystem magic number.  All of the changes were in the IMA > subsystem.  These patches are the result of Christoph's comment on the > original patches saying, "ima has no business looking at either the > name _or_ the magic number." > > Your help in resolving this problem is much appreciated! Meaning, can you ack the fuse flag addition so we can take the series through the IMA tree? thanks, Mimi > > > > > Cc: linux-kernel@vger.kernel.org > > Cc: linux-integrity@vger.kernel.org > > Cc: linux-security-module@vger.kernel.org > > Cc: linux-fsdevel@vger.kernel.org > > Cc: Miklos Szeredi > > Cc: Alexander Viro > > Cc: Mimi Zohar > > Cc: Dmitry Kasatkin > > Cc: James Morris > > Cc: Christoph Hellwig > > Acked-by: "Serge E. Hallyn" > > Acked-by: Seth Forshee > > Tested-by: Dongsu Park > > Signed-off-by: Alban Crequy > > --- > > fs/fuse/inode.c | 2 +- > > include/linux/fs.h | 1 + > > 2 files changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c > > index 624f18bb..0a9e5164 100644 > > --- a/fs/fuse/inode.c > > +++ b/fs/fuse/inode.c > > @@ -1205,7 +1205,7 @@ static void fuse_kill_sb_anon(struct super_block *sb) > > static struct file_system_type fuse_fs_type = { > > .owner = THIS_MODULE, > > .name = "fuse", > > - .fs_flags = FS_HAS_SUBTYPE, > > + .fs_flags = FS_HAS_SUBTYPE | FS_IMA_NO_CACHE, > > .mount = fuse_mount, > > .kill_sb = fuse_kill_sb_anon, > > }; > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > index 511fbaab..ced841ba 100644 > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -2075,6 +2075,7 @@ struct file_system_type { > > #define FS_BINARY_MOUNTDATA 2 > > #define FS_HAS_SUBTYPE 4 > > #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ > > +#define FS_IMA_NO_CACHE 16 /* Force IMA to re-measure, re-appraise, re-audit files */ > > #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ > > struct dentry *(*mount) (struct file_system_type *, int, > > const char *, void *); >