Fix ReadExt4SuperBlock function (#1229)

Previously the function would read bytes from a given file and convert them into internal ext4 super block object, without checking that the read bytes are actually ext4 super block. Fix the behavior by checking ext4 super block magic. Signed-off-by: Maksim An <[email protected]>
microsoft · Nov 23, 2021 · f52c346 · f52c346
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commit f52c346
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diff --git a/ext4/tar2ext4/tar2ext4.go b/ext4/tar2ext4/tar2ext4.go
@@ -272,6 +272,10 @@ func ReadExt4SuperBlock(vhdPath string) (*format.SuperBlock, error) {
 	if err := binary.Read(vhd, binary.LittleEndian, &sb); err != nil {
 		return nil, err
 	}
+	// Make sure the magic bytes are correct.
+	if sb.Magic != format.SuperBlockMagic {
+		return nil, errors.New("not an ext4 file system")
+	}
 	return &sb, nil
 }
 

diff --git a/test/vendor/github.com/Microsoft/hcsshim/ext4/tar2ext4/tar2ext4.go b/test/vendor/github.com/Microsoft/hcsshim/ext4/tar2ext4/tar2ext4.go