[PATCH 2/3] udf: Avoid using corrupted block bitmap buffer

[Jan Kara <jack@xxxxxxx>]

When the filesystem block bitmap is corrupted, we detect the corruption
while loading the bitmap and fail the allocation with error. However the
next allocation from the same bitmap will notice the bitmap buffer is
already loaded and tries to allocate from the bitmap with mixed results
(depending on the exact nature of the bitmap corruption). Fix the
problem by using BH_verified bit to indicate whether the bitmap is valid
or not.

Reported-by: syzbot+5f682cd029581f9edfd1@xxxxxxxxxxxxxxxxxxxxxxxxx
CC: stable@xxxxxxxxxxxxxxx
Fixes: 1e0d4adf17e7 ("udf: Check consistency of Space Bitmap Descriptor")
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 fs/udf/balloc.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index ab3ffc355949..558ad046972a 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -64,8 +64,12 @@ static int read_block_bitmap(struct super_block *sb,
 	}
 
 	for (i = 0; i < count; i++)
-		if (udf_test_bit(i + off, bh->b_data))
+		if (udf_test_bit(i + off, bh->b_data)) {
+			bitmap->s_block_bitmap[bitmap_nr] =
+							ERR_PTR(-EFSCORRUPTED);
+			brelse(bh);
 			return -EFSCORRUPTED;
+		}
 	return 0;
 }
 
@@ -81,8 +85,15 @@ static int __load_block_bitmap(struct super_block *sb,
 			  block_group, nr_groups);
 	}
 
-	if (bitmap->s_block_bitmap[block_group])
+	if (bitmap->s_block_bitmap[block_group]) {
+		/*
+		 * The bitmap failed verification in the past. No point in
+		 * trying again.
+		 */
+		if (IS_ERR(bitmap->s_block_bitmap[block_group]))
+			return PTR_ERR(bitmap->s_block_bitmap[block_group]);
 		return block_group;
+	}
 
 	retval = read_block_bitmap(sb, bitmap, block_group, block_group);
 	if (retval < 0)
-- 
2.35.3