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, 9 insertions, 6 deletions

diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c
index b744c62052b6..a05f44eb8178 100644
--- a/fs/xfs/xfs_acl.c
+++ b/fs/xfs/xfs_acl.c
@@ -242,12 +242,13 @@ xfs_acl_set_mode(
 }
 
 int
-xfs_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
+xfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 	    struct posix_acl *acl, int type)
 {
 	umode_t mode;
 	bool set_mode = false;
 	int error = 0;
+	struct inode *inode = d_inode(dentry);
 
 	if (!acl)
 		goto set_acl;
diff --git a/fs/xfs/xfs_acl.h b/fs/xfs/xfs_acl.h
index 263404d0bfda..dcd176149c7a 100644
--- a/fs/xfs/xfs_acl.h
+++ b/fs/xfs/xfs_acl.h
@@ -11,7 +11,7 @@ struct posix_acl;
 
 #ifdef CONFIG_XFS_POSIX_ACL
 extern struct posix_acl *xfs_get_acl(struct inode *inode, int type, bool rcu);
-extern int xfs_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
+extern int xfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		       struct posix_acl *acl, int type);
 extern int __xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type);
 void xfs_forget_acl(struct inode *inode, const char *name);
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 2e10e1c66ad6..ab266ba65a84 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -651,6 +651,7 @@ xfs_vn_change_ok(
 static int
 xfs_setattr_nonsize(
 	struct user_namespace	*mnt_userns,
+	struct dentry		*dentry,
 	struct xfs_inode	*ip,
 	struct iattr		*iattr)
 {
@@ -757,7 +758,7 @@ xfs_setattr_nonsize(
 	 * 	     Posix ACL code seems to care about this issue either.
 	 */
 	if (mask & ATTR_MODE) {
-		error = posix_acl_chmod(mnt_userns, inode, inode->i_mode);
+		error = posix_acl_chmod(mnt_userns, dentry, inode->i_mode);
 		if (error)
 			return error;
 	}
@@ -779,6 +780,7 @@ out_dqrele:
 STATIC int
 xfs_setattr_size(
 	struct user_namespace	*mnt_userns,
+	struct dentry		*dentry,
 	struct xfs_inode	*ip,
 	struct iattr		*iattr)
 {
@@ -810,7 +812,7 @@ xfs_setattr_size(
 		 * Use the regular setattr path to update the timestamps.
 		 */
 		iattr->ia_valid &= ~ATTR_SIZE;
-		return xfs_setattr_nonsize(mnt_userns, ip, iattr);
+		return xfs_setattr_nonsize(mnt_userns, dentry, ip, iattr);
 	}
 
 	/*
@@ -987,7 +989,7 @@ xfs_vn_setattr_size(
 	error = xfs_vn_change_ok(mnt_userns, dentry, iattr);
 	if (error)
 		return error;
-	return xfs_setattr_size(mnt_userns, ip, iattr);
+	return xfs_setattr_size(mnt_userns, dentry, ip, iattr);
 }
 
 STATIC int
@@ -1019,7 +1021,7 @@ xfs_vn_setattr(
 
 		error = xfs_vn_change_ok(mnt_userns, dentry, iattr);
 		if (!error)
-			error = xfs_setattr_nonsize(mnt_userns, ip, iattr);
+			error = xfs_setattr_nonsize(mnt_userns, dentry, ip, iattr);
 	}
 
 	return error;