RFR: 8305650: os::lasterror incorrectly truncates buffer in os_windows.cpp

[Julian Waters]

On Wed, 5 Apr 2023 13:34:32 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> src/hotspot/os/windows/os_windows.cpp line 2153:
>> 
>>> 2151:     if (n >= len) n = len - 1;
>>> 2152:     strncpy(buf, s, n);
>>> 2153:     buf[n + 1] = '\0';
>> 
>> If n was >= len then you are now indexing outside of buf!
>
> n is always meant to be the length of the buffer data without the null terminator. The check there is meant to enforce exactly that, it sets n = len - 1 because len is a parameter passed to lasterror, and is the size of the buffer the caller handed us. len is supposed to also include space for the null terminator while n is only the length of the actual character data, which is why the - 1 check is there

Unless os::lasterror's len parameter is not supposed to include space for the null terminator, but I couldn't find any documentation or comment that says so. But if that were the case, then this whole code segment would be wrong, not just my change

Ahh, the joys of working with Windows error handling :)

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PR Review Comment: https://git.openjdk.org/jdk/pull/13350#discussion_r1158533914