Unintended memory access when reading the label length?

[presto8]

bcachefs-tools/libbcachefs/super-io.c

Line 1319 in 61f8dc2

if (!strlen(sb->label))

In super-io.c, strlen() is used to determine whether a label is present. However, sb->label is not required to be null-terminated. If it is less than the maximum length, it will be null-terminated. But if it is the maximum length, then it will not be null-terminated, thus causing strlen() to keep reading until it encounters a null character, which will be reading into the other fields of the data structure and perhaps even read outside of the data structure?

I tried it on a filesystem with a 32-length label, and strlen() read 34 bytes and returned 33.

Would if (sb->label[0]) be safer? If the label is present, the first char will be non-zero. And if the label is not present, the first char will be null.