ext4: avoid clearing beyond i_blocks when truncating an inline data file

A missing cast means that when we are truncating a file which is less
than 60 bytes, we don't clear the correct area of memory, and in fact
we can end up truncating the next inode in the inode table, or worse
yet, some other kernel data structure.

Addresses-Coverity-Id: #751987
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

fs/ext4/inline.c

@@ -1928,9 +1928,11 @@ void ext4_inline_data_truncate(struct inode *inode, int *has_inline)
 		}
 
 		/* Clear the content within i_blocks. */
-		if (i_size < EXT4_MIN_INLINE_DATA_SIZE)
-			memset(ext4_raw_inode(&is.iloc)->i_block + i_size, 0,
-					EXT4_MIN_INLINE_DATA_SIZE - i_size);
+		if (i_size < EXT4_MIN_INLINE_DATA_SIZE) {
+			void *p = (void *) ext4_raw_inode(&is.iloc)->i_block;
+			memset(p + i_size, 0,
+			       EXT4_MIN_INLINE_DATA_SIZE - i_size);
+		}
 
 		EXT4_I(inode)->i_inline_size = i_size <
 					EXT4_MIN_INLINE_DATA_SIZE ?