udf: Fix file corruption when appending just after end of preallocated extent

When we append new block just after the end of preallocated extent, the
code in inode_getblk() wrongly determined we're going to use the
preallocated extent which resulted in adding block into a wrong logical
offset in the file. Sequence like this manifests it:

xfs_io -f -c "pwrite 0x2cacf 0xd122" -c "truncate 0x2dd6f" \
  -c "pwrite 0x27fd9 0x69a9" -c "pwrite 0x32981 0x7244" <file>

The code that determined the use of preallocated extent is actually
stale because udf_do_extend_file() does not create preallocation anymore
so after calling that function we are sure there's no usable
preallocation. Just remove the faulty condition.

CC: stable@vger.kernel.org
Fixes: 16d05565 ("udf: Discard preallocation before extending file with a hole")
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/inode.c

@@ -742,19 +742,17 @@ static int inode_getblk(struct inode *inode, struct udf_map_rq *map)
 		c = 0;
 		offset = 0;
 		count += ret;
-		/* We are not covered by a preallocated extent? */
-		if ((laarr[0].extLength & UDF_EXTENT_FLAG_MASK) !=
-						EXT_NOT_RECORDED_ALLOCATED) {
-			/* Is there any real extent? - otherwise we overwrite
-			 * the fake one... */
-			if (count)
-				c = !c;
-			laarr[c].extLength = EXT_NOT_RECORDED_NOT_ALLOCATED |
-				inode->i_sb->s_blocksize;
-			memset(&laarr[c].extLocation, 0x00,
-				sizeof(struct kernel_lb_addr));
-			count++;
-		}
+		/*
+		 * Is there any real extent? - otherwise we overwrite the fake
+		 * one...
+		 */
+		if (count)
+			c = !c;
+		laarr[c].extLength = EXT_NOT_RECORDED_NOT_ALLOCATED |
+			inode->i_sb->s_blocksize;
+		memset(&laarr[c].extLocation, 0x00,
+			sizeof(struct kernel_lb_addr));
+		count++;
 		endnum = c + 1;
 		lastblock = 1;
 	} else {