fcntl receiving -1 from fileno, fcntl failing.

(Also very few spots of negative numgroups for getgroups(),
and fgetc() return, but almost all checking is for fcntl.)

(merged fix for perl #121743 and perl #121745: hopefully
picked up all the fixes-to-fixes from the ticket...)

Fix for Coverity perl5 CIDs 28990..29003,29005..29011,29013,
45354,45363,49926:

Argument cannot be negative (NEGATIVE_RETURNS) fd is
passed to a parameter that cannot be negative.

and CIDs 29004, 29012:
Argument cannot be negative (NEGATIVE_RETURNS)
num_groups is passed to a parameter that cannot be negative

and because of CIDs 29005 and 29006 also CID 28924.

In the first set of issues a fd is retrieved from PerlIO_fileno, and
that is then used in places like fstat(), fchown(), dup(), etc.,
without checking whether the fd is valid (>=0).

In the second set of issues a potentially negative
number is potentially passed to getgroups().

The CIDs 29005 and 29006 were a bit messy: fixing them needed also
resolving CID 28924 where the return value of fstat() was ignored,
and for completeness adding two croak calls (with perldiag updates):
a bit of a waste since it's suidperl code.

1 files changed, 5 insertions, 4 deletions

diff --git a/dist/threads/threads.xs b/dist/threads/threads.xs
index 85371655b2..182cd373e4 100644
--- a/dist/threads/threads.xs
+++ b/dist/threads/threads.xs
@@ -713,11 +713,12 @@ S_ithread_create(
     }
     PERL_SET_CONTEXT(aTHX);
     if (!thread) {
-        int rc;
         MUTEX_UNLOCK(&MY_POOL.create_destruct_mutex);
-        rc = PerlLIO_write(PerlIO_fileno(Perl_error_log),
-                            PL_no_mem, strlen(PL_no_mem));
-        PERL_UNUSED_VAR(rc);
+        int fd = PerlIO_fileno(Perl_error_log);
+        if (fd >= 0) {
+          /* If there's no error_log, we cannot scream about it missing. */
+          PERL_UNUSED_RESULT(PerlLIO_write(fd, PL_no_mem, strlen(PL_no_mem)));
+        }
         my_exit(1);
     }
     Zero(thread, 1, ithread);