RFR (S) 8204055: SIGSEGV in java -XX:

[Thomas Stüfe]

Looks good.

It raises the philosophical question though whether two zero length
strings are completely alike or unlike each other :)

..Thomas

On Thu, May 31, 2018 at 7:55 AM, David Holmes <david.holmes at oracle.com> wrote:
> Bug: https://bugs.openjdk.java.net/browse/JDK-8204055
> webrev: http://cr.openjdk.java.net/~dholmes/8204055/webrev/
>
>
> The SEGV was introduced with the fuzzy matching flag logic refactoring in
> JDK-8198554. In:
>
> double StringUtils::similarity(const char* str1, size_t len1, const
>                                char* str2, size_t len2) {
>   size_t total = len1 + len2;
>
>   size_t hit = 0;
>   for (size_t i = 0; i < len1 - 1; i++) {
>     for (size_t j = 0; j < len2 - 1; j++) {
>       if ((str1[i] == str2[j]) && (str1[i+1] == str2[j+1])) {
>         ++hit;
>         break;
>       }
>     }
>   }
>
> If len2 is zero (which it is in this case) we have passed it as an unsigned
> size_t, so len2-1 gives a massive positive value and so we enter the loop
> and try to access str2[n] for some n>0 and we get a SEGV.
>
> The original code had:
>
> - for (int j = 0; j < (int) len2 -1; ++j) {
>
> so the huge positive value reverted to a small negative value and we don't
> enter the loop.
>
> The fix applied is to check explicitly for lengths of zero.
>
> Added missing testcases to:
>
> test/hotspot/gtest/logging/test_logConfiguration.cpp
> test/hotspot/jtreg/runtime/CommandLine/UnrecognizedVMOption.java
>
> verified they both crash before the fix.
>
> Testing (in progress): tier1,2,3 per mach5 CI
>
> Thanks,
> David