udf: Avoid using corrupted block bitmap buffer

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@syzkaller.appspotmail.com
CC: stable@vger.kernel.org
Link: https://patch.msgid.link/20240617154201.29512-2-jack@suse.cz
Fixes: 1e0d4ad ("udf: Check consistency of Space Bitmap Descriptor")
Signed-off-by: Jan Kara <jack@suse.cz>

Author: jankara

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)

fs/udf/super.c

@@ -336,7 +336,8 @@ static void udf_sb_free_bitmap(struct udf_bitmap *bitmap)
 	int nr_groups = bitmap->s_nr_groups;
 
 	for (i = 0; i < nr_groups; i++)
-		brelse(bitmap->s_block_bitmap[i]);
+		if (!IS_ERR_OR_NULL(bitmap->s_block_bitmap[i]))
+			brelse(bitmap->s_block_bitmap[i]);
 
 	kvfree(bitmap);
 }