ubifs: Limit number of xattrs per inode

Since we have to write one deletion inode per xattr
into the journal, limit the max number of xattrs.

In theory UBIFS supported up to 65535 xattrs per inode.
But this never worked correctly, expect no powercuts happened.
Now we support only as many xattrs as we can store in 50% of a
LEB.
Even for tiny flashes this allows dozens of xattrs per inode,
which is for an embedded filesystem still fine.

In case someone has existing inodes with much more xattrs, it is
still possible to delete them.
UBIFS will fall back to an non-atomic deletion mode.

Reported-by: Stefan Agner <stefan@agner.ch>
Fixes: 1e51764a3c2ac ("UBIFS: add new flash file system")
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 64 insertions, 7 deletions

diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
index f5ad1ede7990..acab3181ab35 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -61,12 +61,6 @@
 #include <linux/xattr.h>
 
 /*
- * Limit the number of extended attributes per inode so that the total size
- * (@xattr_size) is guaranteeded to fit in an 'unsigned int'.
- */
-#define MAX_XATTRS_PER_INODE 65535
-
-/*
  * Extended attribute type constants.
  *
  * USER_XATTR: user extended attribute ("user.*")
@@ -106,7 +100,7 @@ static int create_xattr(struct ubifs_info *c, struct inode *host,
 				.new_ino_d = ALIGN(size, 8), .dirtied_ino = 1,
 				.dirtied_ino_d = ALIGN(host_ui->data_len, 8) };
 
-	if (host_ui->xattr_cnt >= MAX_XATTRS_PER_INODE) {
+	if (host_ui->xattr_cnt >= ubifs_xattr_max_cnt(c)) {
 		ubifs_err(c, "inode %lu already has too many xattrs (%d), cannot create more",
 			  host->i_ino, host_ui->xattr_cnt);
 		return -ENOSPC;
@@ -507,6 +501,69 @@ out_cancel:
 	return err;
 }
 
+int ubifs_purge_xattrs(struct inode *host)
+{
+	union ubifs_key key;
+	struct ubifs_info *c = host->i_sb->s_fs_info;
+	struct ubifs_dent_node *xent, *pxent = NULL;
+	struct inode *xino;
+	struct fscrypt_name nm = {0};
+	int err;
+
+	if (ubifs_inode(host)->xattr_cnt < ubifs_xattr_max_cnt(c))
+		return 0;
+
+	ubifs_warn(c, "inode %lu has too many xattrs, doing a non-atomic deletion",
+		   host->i_ino);
+
+	lowest_xent_key(c, &key, host->i_ino);
+	while (1) {
+		xent = ubifs_tnc_next_ent(c, &key, &nm);
+		if (IS_ERR(xent)) {
+			err = PTR_ERR(xent);
+			break;
+		}
+
+		fname_name(&nm) = xent->name;
+		fname_len(&nm) = le16_to_cpu(xent->nlen);
+
+		xino = ubifs_iget(c->vfs_sb, xent->inum);
+		if (IS_ERR(xino)) {
+			err = PTR_ERR(xino);
+			ubifs_err(c, "dead directory entry '%s', error %d",
+				  xent->name, err);
+			ubifs_ro_mode(c, err);
+			kfree(pxent);
+			return err;
+		}
+
+		ubifs_assert(c, ubifs_inode(xino)->xattr);
+
+		clear_nlink(xino);
+		err = remove_xattr(c, host, xino, &nm);
+		if (err) {
+			kfree(pxent);
+			iput(xino);
+			ubifs_err(c, "cannot remove xattr, error %d", err);
+			return err;
+		}
+
+		iput(xino);
+
+		kfree(pxent);
+		pxent = xent;
+		key_read(c, &xent->key, &key);
+	}
+
+	kfree(pxent);
+	if (err != -ENOENT) {
+		ubifs_err(c, "cannot find next direntry, error %d", err);
+		return err;
+	}
+
+	return 0;
+}
+
 /**
  * ubifs_evict_xattr_inode - Evict an xattr inode.
  * @c: UBIFS file-system description object