Merge tag 'ovl-update-6.18' of git://git.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs

Pull overlayfs updates from Amir Goldstein:

 - Work by André Almeida to support case-insensitive overlayfs

   Underlying case-insensitive filesystems casefolding is per directory,
   but for overlayfs it is all-or-nothing. It supports layers where all
   directories are casefolded (with same encoding) or layers where no
   directories are casefolded.

 - A fix for a "bug" in Neil's ovl directory lock changes, which only
   manifested itself with casefold enabled layers which may return an
   unhashed negative dentry from lookup.

* tag 'ovl-update-6.18' of git://git.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs:
  ovl: make sure that ovl_create_real() returns a hashed dentry
  ovl: Support mounting case-insensitive enabled layers
  ovl: Check for casefold consistency when creating new dentries
  ovl: Add S_CASEFOLD as part of the inode flag to be copied
  ovl: Set case-insensitive dentry operations for ovl sb
  ovl: Ensure that all layers have the same encoding
  ovl: Create ovl_casefold() to support casefolded strncmp()
  ovl: Prepare for mounting case-insensitive enabled layers
  fs: Create sb_same_encoding() helper
  fs: Create sb_encoding() helper

Author: torvalds

fs/overlayfs/copy_up.c

@@ -670,7 +670,7 @@ static int ovl_copy_up_metadata(struct ovl_copy_up_ctx *c, struct dentry *temp)
 	if (err)
 		return err;
 
-	if (inode->i_flags & OVL_COPY_I_FLAGS_MASK &&
+	if (inode->i_flags & OVL_FATTR_I_FLAGS_MASK &&
 	    (S_ISREG(c->stat.mode) || S_ISDIR(c->stat.mode))) {
 		/*
 		 * Copy the fileattr inode flags that are the source of already

fs/overlayfs/dir.c

@@ -187,6 +187,13 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
 			/* mkdir is special... */
 			newdentry =  ovl_do_mkdir(ofs, dir, newdentry, attr->mode);
 			err = PTR_ERR_OR_ZERO(newdentry);
+			/* expect to inherit casefolding from workdir/upperdir */
+			if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) {
+				pr_warn_ratelimited("wrong inherited casefold (%pd2)\n",
+						    newdentry);
+				dput(newdentry);
+				err = -EINVAL;
+			}
 			break;
 
 		case S_IFCHR:
@@ -205,12 +212,32 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
 			err = -EPERM;
 		}
 	}
-	if (!err && WARN_ON(!newdentry->d_inode)) {
+	if (err)
+		goto out;
+
+	if (WARN_ON(!newdentry->d_inode)) {
 		/*
 		 * Not quite sure if non-instantiated dentry is legal or not.
 		 * VFS doesn't seem to care so check and warn here.
 		 */
 		err = -EIO;
+	} else if (d_unhashed(newdentry)) {
+		struct dentry *d;
+		/*
+		 * Some filesystems (i.e. casefolded) may return an unhashed
+		 * negative dentry from the ovl_lookup_upper() call before
+		 * ovl_create_real().
+		 * In that case, lookup again after making the newdentry
+		 * positive, so ovl_create_upper() always returns a hashed
+		 * positive dentry.
+		 */
+		d = ovl_lookup_upper(ofs, newdentry->d_name.name, parent,
+				     newdentry->d_name.len);
+		dput(newdentry);
+		if (IS_ERR_OR_NULL(d))
+			err = d ? PTR_ERR(d) : -ENOENT;
+		else
+			return d;
 	}
 out:
 	if (err) {

fs/overlayfs/inode.c

@@ -1277,6 +1277,7 @@ struct inode *ovl_get_inode(struct super_block *sb,
 	}
 	ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev);
 	ovl_inode_init(inode, oip, ino, fsid);
+	WARN_ON_ONCE(!!IS_CASEFOLDED(inode) != ofs->casefold);
 
 	if (upperdentry && ovl_is_impuredir(sb, upperdentry))
 		ovl_set_flag(OVL_IMPURE, inode);

fs/overlayfs/namei.c

@@ -239,13 +239,14 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 	char val;
 
 	/*
-	 * We allow filesystems that are case-folding capable but deny composing
-	 * ovl stack from case-folded directories. If someone has enabled case
-	 * folding on a directory on underlying layer, the warranty of the ovl
-	 * stack is voided.
+	 * We allow filesystems that are case-folding capable as long as the
+	 * layers are consistently enabled in the stack, enabled for every dir
+	 * or disabled in all dirs. If someone has modified case folding on a
+	 * directory on underlying layer, the warranty of the ovl stack is
+	 * voided.
 	 */
-	if (ovl_dentry_casefolded(base)) {
-		warn = "case folded parent";
+	if (ofs->casefold != ovl_dentry_casefolded(base)) {
+		warn = "parent wrong casefold";
 		err = -ESTALE;
 		goto out_warn;
 	}
@@ -259,8 +260,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 		goto out_err;
 	}
 
-	if (ovl_dentry_casefolded(this)) {
-		warn = "case folded child";
+	if (ofs->casefold != ovl_dentry_casefolded(this)) {
+		warn = "child wrong casefold";
 		err = -EREMOTE;
 		goto out_warn;
 	}

fs/overlayfs/overlayfs.h

@@ -820,10 +820,12 @@ struct inode *ovl_get_inode(struct super_block *sb,
 			    struct ovl_inode_params *oip);
 void ovl_copyattr(struct inode *to);
 
+/* vfs fileattr flags read from overlay.protattr xattr to ovl inode */
+#define OVL_PROT_I_FLAGS_MASK  (S_APPEND | S_IMMUTABLE)
+/* vfs fileattr flags copied from real to ovl inode */
+#define OVL_FATTR_I_FLAGS_MASK (OVL_PROT_I_FLAGS_MASK | S_SYNC | S_NOATIME)
 /* vfs inode flags copied from real to ovl inode */
-#define OVL_COPY_I_FLAGS_MASK	(S_SYNC | S_NOATIME | S_APPEND | S_IMMUTABLE)
-/* vfs inode flags read from overlay.protattr xattr to ovl inode */
-#define OVL_PROT_I_FLAGS_MASK	(S_APPEND | S_IMMUTABLE)
+#define OVL_COPY_I_FLAGS_MASK  (OVL_FATTR_I_FLAGS_MASK | S_CASEFOLD)
 
 /*
  * fileattr flags copied from lower to upper inode on copy up.

fs/overlayfs/ovl_entry.h

@@ -91,6 +91,7 @@ struct ovl_fs {
 	struct mutex whiteout_lock;
 	/* r/o snapshot of upperdir sb's only taken on volatile mounts */
 	errseq_t errseq;
+	bool casefold;
 };
 
 /* Number of lower layers, not including data-only layers */

fs/overlayfs/params.c

@@ -276,17 +276,26 @@ static int ovl_mount_dir(const char *name, struct path *path)
 static int ovl_mount_dir_check(struct fs_context *fc, const struct path *path,
 			       enum ovl_opt layer, const char *name, bool upper)
 {
+	bool is_casefolded = ovl_dentry_casefolded(path->dentry);
 	struct ovl_fs_context *ctx = fc->fs_private;
+	struct ovl_fs *ofs = fc->s_fs_info;
 
 	if (!d_is_dir(path->dentry))
 		return invalfc(fc, "%s is not a directory", name);
 
 	/*
 	 * Allow filesystems that are case-folding capable but deny composing
-	 * ovl stack from case-folded directories.
+	 * ovl stack from inconsistent case-folded directories.
 	 */
-	if (ovl_dentry_casefolded(path->dentry))
-		return invalfc(fc, "case-insensitive directory on %s not supported", name);
+	if (!ctx->casefold_set) {
+		ofs->casefold = is_casefolded;
+		ctx->casefold_set = true;
+	}
+
+	if (ofs->casefold != is_casefolded) {
+		return invalfc(fc, "case-%ssensitive directory on %s is inconsistent",
+			       is_casefolded ? "in" : "", name);
+	}
 
 	if (ovl_dentry_weird(path->dentry))
 		return invalfc(fc, "filesystem on %s not supported", name);

fs/overlayfs/params.h

@@ -33,6 +33,7 @@ struct ovl_fs_context {
 	struct ovl_opt_set set;
 	struct ovl_fs_context_layer *lower;
 	char *lowerdir_all; /* user provided lowerdir string */
+	bool casefold_set;
 };
 
 int ovl_init_fs_context(struct fs_context *fc);