[PATCH] udf: fix WARN_ON_ONCE in udf_map_block on concurrent expand failure

[golasch18]

From: Lukas Blesser <golasch18@xxxxxx>

udf_direct_IO() falls back to buffered I/O for in-ICB files, but it
checks i_alloc_type without holding i_data_sem. If a concurrent write
fails to expand the file, udf_expand_file_adinicb() restores inline
allocation, so udf_map_block() can observe ICBTAG_FLAG_AD_IN_ICB after
the caller checked and hit the WARN_ON_ONCE() for a transient state.

Move the allocation-type check under the down_read() udf_map_block()
already takes on the lookup path and return -EFSCORRUPTED gracefully
instead of warning.

Reported-by: syzbot+de2fef01040748da6822@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=de2fef01040748da6822
Signed-off-by: Lukas Blesser <golasch18@xxxxxx>
---
 fs/udf/inode.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index e45e546a7..cea8d5c4d 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -352,9 +352,6 @@ static int udf_map_block(struct inode *inode, struct udf_map_rq *map)
 	int ret;
 	struct udf_inode_info *iinfo = UDF_I(inode);
 
-	if (WARN_ON_ONCE(iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB))
-		return -EFSCORRUPTED;
-
 	map->oflags = 0;
 	if (!(map->iflags & UDF_MAP_CREATE)) {
 		struct kernel_lb_addr eloc;
@@ -364,6 +361,18 @@ static int udf_map_block(struct inode *inode, struct udf_map_rq *map)
 		int8_t etype;
 
 		down_read(&iinfo->i_data_sem);
+		/*
+		 * The allocation type may have changed back to in-ICB
+		 * after a caller checked it without holding i_data_sem:
+		 * e.g. a concurrent expand failure restores inline
+		 * allocation in udf_expand_file_adinicb(). Recheck here
+		 * under i_data_sem and fail gracefully instead of
+		 * warning about a transient state.
+		 */
+		if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
+			ret = -EFSCORRUPTED;
+			goto out_read;
+		}
 		ret = inode_bmap(inode, map->lblk, &epos, &eloc, &elen, &offset,
 				 &etype);
 		if (ret < 0)
-- 
2.55.0