udf: Fix preallocation discarding at indirect extent boundary

When preallocation extent is the first one in the extent block, the
code would corrupt extent tree header instead. Fix the problem and use
udf_delete_aext() for deleting extent to avoid some code duplication.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/truncate.c

@@ -120,60 +120,41 @@ void udf_truncate_tail_extent(struct inode *inode)
 
 void udf_discard_prealloc(struct inode *inode)
 {
-	struct extent_position epos = { NULL, 0, {0, 0} };
+	struct extent_position epos = {};
+	struct extent_position prev_epos = {};
 	struct kernel_lb_addr eloc;
 	uint32_t elen;
 	uint64_t lbcount = 0;
 	int8_t etype = -1, netype;
-	int adsize;
 	struct udf_inode_info *iinfo = UDF_I(inode);
 
 	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB ||
 	    inode->i_size == iinfo->i_lenExtents)
 		return;
 
-	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_SHORT)
-		adsize = sizeof(struct short_ad);
-	else if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_LONG)
-		adsize = sizeof(struct long_ad);
-	else
-		adsize = 0;
-
 	epos.block = iinfo->i_location;
 
 	/* Find the last extent in the file */
-	while ((netype = udf_next_aext(inode, &epos, &eloc, &elen, 1)) != -1) {
-		etype = netype;
+	while ((netype = udf_next_aext(inode, &epos, &eloc, &elen, 0)) != -1) {
+		brelse(prev_epos.bh);
+		prev_epos = epos;
+		if (prev_epos.bh)
+			get_bh(prev_epos.bh);
+
+		etype = udf_next_aext(inode, &epos, &eloc, &elen, 1);
 		lbcount += elen;
 	}
 	if (etype == (EXT_NOT_RECORDED_ALLOCATED >> 30)) {
-		epos.offset -= adsize;
 		lbcount -= elen;
-		extent_trunc(inode, &epos, &eloc, etype, elen, 0);
-		if (!epos.bh) {
-			iinfo->i_lenAlloc =
-				epos.offset -
-				udf_file_entry_alloc_offset(inode);
-			mark_inode_dirty(inode);
-		} else {
-			struct allocExtDesc *aed =
-				(struct allocExtDesc *)(epos.bh->b_data);
-			aed->lengthAllocDescs =
-				cpu_to_le32(epos.offset -
-					    sizeof(struct allocExtDesc));
-			if (!UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_STRICT) ||
-			    UDF_SB(inode->i_sb)->s_udfrev >= 0x0201)
-				udf_update_tag(epos.bh->b_data, epos.offset);
-			else
-				udf_update_tag(epos.bh->b_data,
-					       sizeof(struct allocExtDesc));
-			mark_buffer_dirty_inode(epos.bh, inode);
-		}
+		udf_delete_aext(inode, prev_epos);
+		udf_free_blocks(inode->i_sb, inode, &eloc, 0,
+				DIV_ROUND_UP(elen, 1 << inode->i_blkbits));
 	}
 	/* This inode entry is in-memory only and thus we don't have to mark
 	 * the inode dirty */
 	iinfo->i_lenExtents = lbcount;
 	brelse(epos.bh);
+	brelse(prev_epos.bh);
 }
 
 static void udf_update_alloc_ext_desc(struct inode *inode,