libext2fs: initialize i_extra_isize when writing EAs

If i_extra_isize is zero when we try to write extended attributes,
we'll end up writing the EA magic into the i_extra_isize field, which
causes a subsequent crash on big endian systems (when we try to write
0xEA02 bytes past the inode!).  Therefore when the field is zero, set
i_extra_isize to the desired extra_isize size, zero those bytes, and
write the EAs after the end of the extended inode.

v2: Don't bother if we have 128b inodes, and ensure that the value
is 32b-aligned so that the EA magic starts on a 32b boundary.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

lib/ext2fs/ext_attr.c

@@ -519,6 +519,18 @@ errcode_t ext2fs_xattrs_write(struct ext2_xattr_handle *handle)
 	if (err)
 		goto out;
 
+	/* If extra_isize isn't set, we need to set it now */
+	if (inode->i_extra_isize == 0 &&
+	    EXT2_INODE_SIZE(handle->fs->super) > EXT2_GOOD_OLD_INODE_SIZE) {
+		char *p = (char *)inode;
+		size_t extra = handle->fs->super->s_want_extra_isize;
+
+		if (extra == 0)
+			extra = sizeof(__u32);
+		memset(p + EXT2_GOOD_OLD_INODE_SIZE, 0, extra);
+		inode->i_extra_isize = extra;
+	}
+
 	move_inline_data_to_front(handle);
 
 	x = handle->attrs;

tests/f_write_ea_no_extra_isize/expect.1

@@ -0,0 +1,12 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Directory inode 12, block #0, offset 4: directory corrupted
+Salvage? yes
+
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+
+test_filesys: ***** FILE SYSTEM WAS MODIFIED *****
+test_filesys: 12/128 files (0.0% non-contiguous), 17/512 blocks
+Exit status is 1

tests/f_write_ea_no_extra_isize/expect.2

@@ -0,0 +1,7 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+test_filesys: 12/128 files (0.0% non-contiguous), 17/512 blocks
+Exit status is 0

tests/f_write_ea_no_extra_isize/name

@@ -0,0 +1 @@
+write EA when i_extra_size is zero