[RFC PATCH v4 1/2] fuse: introduce new fs_type flag FS_IMA_NO_CACHE

[Dongsu Park]

From: Alban Crequy <alban at kinvolk.io>

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.

Cc: linux-kernel at vger.kernel.org
Cc: linux-integrity at vger.kernel.org
Cc: linux-security-module at vger.kernel.org
Cc: linux-fsdevel at vger.kernel.org
Cc: Miklos Szeredi <miklos at szeredi.hu>
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: Mimi Zohar <zohar at linux.vnet.ibm.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin at gmail.com>
Cc: James Morris <jmorris at namei.org>
Cc: Christoph Hellwig <hch at infradead.org>
Acked-by: "Serge E. Hallyn" <serge at hallyn.com>
Acked-by: Seth Forshee <seth.forshee at canonical.com>
Tested-by: Dongsu Park <dongsu at kinvolk.io>
Signed-off-by: Alban Crequy <alban at kinvolk.io>
---
 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 *);
-- 
2.13.6

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