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, 10 insertions, 7 deletions

diff --git a/fs/reiserfs/acl.h b/fs/reiserfs/acl.h
index d9052b8ce6dd..29c503a06db4 100644
--- a/fs/reiserfs/acl.h
+++ b/fs/reiserfs/acl.h
@@ -49,9 +49,9 @@ static inline int reiserfs_acl_count(size_t size)
 
 #ifdef CONFIG_REISERFS_FS_POSIX_ACL
 struct posix_acl *reiserfs_get_acl(struct inode *inode, int type, bool rcu);
-int reiserfs_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
+int reiserfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		     struct posix_acl *acl, int type);
-int reiserfs_acl_chmod(struct inode *inode);
+int reiserfs_acl_chmod(struct dentry *dentry);
 int reiserfs_inherit_default_acl(struct reiserfs_transaction_handle *th,
 				 struct inode *dir, struct dentry *dentry,
 				 struct inode *inode);
@@ -63,7 +63,7 @@ int reiserfs_cache_default_acl(struct inode *dir);
 #define reiserfs_get_acl NULL
 #define reiserfs_set_acl NULL
 
-static inline int reiserfs_acl_chmod(struct inode *inode)
+static inline int reiserfs_acl_chmod(struct dentry *dentry)
 {
 	return 0;
 }
diff --git a/fs/reiserfs/inode.c b/fs/reiserfs/inode.c
index b9580a6515ee..c7d1fa526dea 100644
--- a/fs/reiserfs/inode.c
+++ b/fs/reiserfs/inode.c
@@ -3404,7 +3404,7 @@ int reiserfs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 
 	if (!error && reiserfs_posixacl(inode->i_sb)) {
 		if (attr->ia_valid & ATTR_MODE)
-			error = reiserfs_acl_chmod(inode);
+			error = reiserfs_acl_chmod(dentry);
 	}
 
 out:
diff --git a/fs/reiserfs/xattr_acl.c b/fs/reiserfs/xattr_acl.c
index d6fcddc46f5b..966ba48e33ec 100644
--- a/fs/reiserfs/xattr_acl.c
+++ b/fs/reiserfs/xattr_acl.c
@@ -18,7 +18,7 @@ static int __reiserfs_set_acl(struct reiserfs_transaction_handle *th,
 
 
 int
-reiserfs_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
+reiserfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		 struct posix_acl *acl, int type)
 {
 	int error, error2;
@@ -26,6 +26,7 @@ reiserfs_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
 	size_t jcreate_blocks;
 	int size = acl ? posix_acl_xattr_size(acl->a_count) : 0;
 	int update_mode = 0;
+	struct inode *inode = d_inode(dentry);
 	umode_t mode = inode->i_mode;
 
 	/*
@@ -396,13 +397,15 @@ int reiserfs_cache_default_acl(struct inode *inode)
 /*
  * Called under i_mutex
  */
-int reiserfs_acl_chmod(struct inode *inode)
+int reiserfs_acl_chmod(struct dentry *dentry)
 {
+	struct inode *inode = d_inode(dentry);
+
 	if (IS_PRIVATE(inode))
 		return 0;
 	if (get_inode_sd_version(inode) == STAT_DATA_V1 ||
 	    !reiserfs_posixacl(inode->i_sb))
 		return 0;
 
-	return posix_acl_chmod(&init_user_ns, inode, inode->i_mode);
+	return posix_acl_chmod(&init_user_ns, dentry, inode->i_mode);
 }