[PATCH v3 2/2] udf: Fix race between file type conversion and writeback

[Jan Kara <jack@suse.cz>]

udf_setsize() can race with udf_writepages() as follows:

udf_setsize()			udf_writepages()
				  if (iinfo->i_alloc_type ==
						ICBTAG_FLAG_AD_IN_ICB)
  err = udf_expand_file_adinicb(inode);
  err = udf_extend_file(inode, newsize);
				    udf_adinicb_writepages()
				      memcpy_from_file_folio() - crash
					because inode size is too big.

Fix the problem by rechecking file type under folio lock in
udf_writepages() which properly serializes with
udf_expand_file_adinicb(). Since it is quite difficult to implement this
locking with current writeback_iter() logic, let's just opencode the
logic necessary to prepare (the only) folio the inode can have for
writeback.

Reported-by: Jianzhou Zhao <luckd0g@163.com>
Link: https://lore.kernel.org/all/f622c01.67ac.19cdbdd777d.Coremail.luckd0g@163.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/udf/inode.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 7fae8002344a..23e894092dab 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -181,22 +181,23 @@ static void udf_write_failed(struct address_space *mapping, loff_t to)
 	}
 }
 
-static int udf_adinicb_writepages(struct address_space *mapping,
-		      struct writeback_control *wbc)
+static int udf_handle_page_wb(struct folio *folio,
+			      struct writeback_control *wbc)
 {
-	struct inode *inode = mapping->host;
+	struct inode *inode = folio->mapping->host;
 	struct udf_inode_info *iinfo = UDF_I(inode);
-	struct folio *folio = NULL;
-	int error = 0;
 
-	while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
-		BUG_ON(!folio_test_locked(folio));
-		BUG_ON(folio->index != 0);
-		memcpy_from_file_folio(iinfo->i_data + iinfo->i_lenEAttr, folio,
-				0, i_size_read(inode));
-		folio_unlock(folio);
-	}
+	/*
+	 * Inodes in the normal format are handled by the generic code. This
+	 * check is race-free as the folio lock protects us from inode type
+	 * conversion.
+	 */
+	if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB)
+		return 1;
 
+	memcpy_from_file_folio(iinfo->i_data + iinfo->i_lenEAttr, folio,
+				0, i_size_read(inode));
+	folio_unlock(folio);
 	mark_inode_dirty(inode);
 	return 0;
 }
@@ -204,12 +205,8 @@ static int udf_adinicb_writepages(struct address_space *mapping,
 static int udf_writepages(struct address_space *mapping,
 			  struct writeback_control *wbc)
 {
-	struct inode *inode = mapping->host;
-	struct udf_inode_info *iinfo = UDF_I(inode);
-
-	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB)
-		return udf_adinicb_writepages(mapping, wbc);
-	return mpage_writepages(mapping, wbc, udf_get_block_wb);
+	return __mpage_writepages(mapping, wbc, udf_get_block_wb,
+				  udf_handle_page_wb);
 }
 
 static void udf_adinicb_read_folio(struct folio *folio)
-- 
2.51.0