fs: pass dentry to set acl method

The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

Since some filesystem rely on the dentry being available to them when
setting posix acls (e.g., 9p and cifs) they cannot rely on set acl inode
operation. But since ->set_acl() is required in order to use the generic
posix acl xattr handlers filesystems that do not implement this inode
operation cannot use the handler and need to implement their own
dedicated posix acl handlers.

Update the ->set_acl() inode method to take a dentry argument. This
allows all filesystems to rely on ->set_acl().

As far as I can tell all codepaths can be switched to rely on the dentry
instead of just the inode. Note that the original motivation for passing
the dentry separate from the inode instead of just the dentry in the
xattr handlers was because of security modules that call
security_d_instantiate(). This hook is called during
d_instantiate_new(), d_add(), __d_instantiate_anon(), and
d_splice_alias() to initialize the inode's security context and possibly
to set security.* xattrs. Since this only affects security.* xattrs this
is completely irrelevant for posix acls.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

3 files changed, 4 insertions, 3 deletions

diff --git a/fs/ceph/acl.c b/fs/ceph/acl.c
index f4fc8e0b847c..c7e8dd5b58d4 100644
--- a/fs/ceph/acl.c
+++ b/fs/ceph/acl.c
@@ -85,13 +85,14 @@ retry:
 	return acl;
 }
 
-int ceph_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
+int ceph_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		 struct posix_acl *acl, int type)
 {
 	int ret = 0, size = 0;
 	const char *name = NULL;
 	char *value = NULL;
 	struct iattr newattrs;
+	struct inode *inode = d_inode(dentry);
 	struct timespec64 old_ctime = inode->i_ctime;
 	umode_t new_mode = inode->i_mode, old_mode = inode->i_mode;
 
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 4af5e55abc15..ca8aef906dc1 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -2255,7 +2255,7 @@ int ceph_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 	err = __ceph_setattr(inode, attr);
 
 	if (err >= 0 && (attr->ia_valid & ATTR_MODE))
-		err = posix_acl_chmod(&init_user_ns, inode, attr->ia_mode);
+		err = posix_acl_chmod(&init_user_ns, dentry, attr->ia_mode);
 
 	return err;
 }
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 40630e6f691c..50e57a1fa32f 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -1117,7 +1117,7 @@ void ceph_release_acl_sec_ctx(struct ceph_acl_sec_ctx *as_ctx);
 
 struct posix_acl *ceph_get_acl(struct inode *, int, bool);
 int ceph_set_acl(struct user_namespace *mnt_userns,
-		 struct inode *inode, struct posix_acl *acl, int type);
+		 struct dentry *dentry, struct posix_acl *acl, int type);
 int ceph_pre_init_acls(struct inode *dir, umode_t *mode,
 		       struct ceph_acl_sec_ctx *as_ctx);
 void ceph_init_inode_acls(struct inode *inode,