Btrfs: fix listxattrs not listing all xattrs packed in the same item

In the listxattrs handler, we were not listing all the xattrs that are
packed in the same btree item, which happens when multiple xattrs have
a name that when crc32c hashed produce the same checksum value.

Fix this by processing them all.

The following test case for xfstests reproduces the issue:

  seq=`basename $0`
  seqres=$RESULT_DIR/$seq
  echo "QA output created by $seq"
  tmp=/tmp/$$
  status=1	# failure is the default!
  trap "_cleanup; exit \$status" 0 1 2 3 15

  _cleanup()
  {
      cd /
      rm -f $tmp.*
  }

  # get standard environment, filters and checks
  . ./common/rc
  . ./common/filter
  . ./common/attr

  # real QA test starts here
  _supported_fs generic
  _supported_os Linux
  _require_scratch
  _require_attrs

  rm -f $seqres.full

  _scratch_mkfs >>$seqres.full 2>&1
  _scratch_mount

  # Create our test file with a few xattrs. The first 3 xattrs have a name
  # that when given as input to a crc32c function result in the same checksum.
  # This made btrfs list only one of the xattrs through listxattrs system call
  # (because it packs xattrs with the same name checksum into the same btree
  # item).
  touch $SCRATCH_MNT/testfile
  $SETFATTR_PROG -n user.foobar -v 123 $SCRATCH_MNT/testfile
  $SETFATTR_PROG -n user.WvG1c1Td -v qwerty $SCRATCH_MNT/testfile
  $SETFATTR_PROG -n user.J3__T_Km3dVsW_ -v hello $SCRATCH_MNT/testfile
  $SETFATTR_PROG -n user.something -v pizza $SCRATCH_MNT/testfile
  $SETFATTR_PROG -n user.ping -v pong $SCRATCH_MNT/testfile

  # Now call getfattr with --dump, which calls the listxattrs system call.
  # It should list all the xattrs we have set before.
  $GETFATTR_PROG --absolute-names --dump $SCRATCH_MNT/testfile | _filter_scratch

  status=0
  exit
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/xattr.c

@@ -260,16 +260,12 @@ int __btrfs_setxattr(struct btrfs_trans_handle *trans,
 
 ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
 {
-	struct btrfs_key key, found_key;
+	struct btrfs_key key;
 	struct inode *inode = d_inode(dentry);
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_path *path;
-	struct extent_buffer *leaf;
-	struct btrfs_dir_item *di;
-	int ret = 0, slot;
+	int ret = 0;
 	size_t total_size = 0, size_left = size;
-	unsigned long name_ptr;
-	size_t name_len;
 
 	/*
 	 * ok we want all objects associated with this id.
@@ -291,6 +287,13 @@ ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
 		goto err;
 
 	while (1) {
+		struct extent_buffer *leaf;
+		int slot;
+		struct btrfs_dir_item *di;
+		struct btrfs_key found_key;
+		u32 item_size;
+		u32 cur;
+
 		leaf = path->nodes[0];
 		slot = path->slots[0];
 
@@ -316,31 +319,45 @@ ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
 		if (found_key.type > BTRFS_XATTR_ITEM_KEY)
 			break;
 		if (found_key.type < BTRFS_XATTR_ITEM_KEY)
-			goto next;
+			goto next_item;
 
 		di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
-		if (verify_dir_item(root, leaf, di))
-			goto next;
-
-		name_len = btrfs_dir_name_len(leaf, di);
-		total_size += name_len + 1;
+		item_size = btrfs_item_size_nr(leaf, slot);
+		cur = 0;
+		while (cur < item_size) {
+			u16 name_len = btrfs_dir_name_len(leaf, di);
+			u16 data_len = btrfs_dir_data_len(leaf, di);
+			u32 this_len = sizeof(*di) + name_len + data_len;
+			unsigned long name_ptr = (unsigned long)(di + 1);
+
+			if (verify_dir_item(root, leaf, di)) {
+				ret = -EIO;
+				goto err;
+			}
 
-		/* we are just looking for how big our buffer needs to be */
-		if (!size)
-			goto next;
+			total_size += name_len + 1;
+			/*
+			 * We are just looking for how big our buffer needs to
+			 * be.
+			 */
+			if (!size)
+				goto next;
 
-		if (!buffer || (name_len + 1) > size_left) {
-			ret = -ERANGE;
-			goto err;
-		}
+			if (!buffer || (name_len + 1) > size_left) {
+				ret = -ERANGE;
+				goto err;
+			}
 
-		name_ptr = (unsigned long)(di + 1);
-		read_extent_buffer(leaf, buffer, name_ptr, name_len);
-		buffer[name_len] = '\0';
+			read_extent_buffer(leaf, buffer, name_ptr, name_len);
+			buffer[name_len] = '\0';
 
-		size_left -= name_len + 1;
-		buffer += name_len + 1;
+			size_left -= name_len + 1;
+			buffer += name_len + 1;
 next:
+			cur += this_len;
+			di = (struct btrfs_dir_item *)((char *)di + this_len);
+		}
+next_item:
 		path->slots[0]++;
 	}
 	ret = total_size;