RT #127742: Hash keys are limited to 2 GB - throw an exception if hash keys are too long

We currently require hash keys to be less than 2**31 bytes long. But (a)
nothing actually tries to enforce that, and (b) if a Perl program tries to
create a hash with such a key (using a 64-bit system), we miscalculate the
size of a memory block, yielding a panic:

$ ./perl -e '+{ "x" x 2**31, undef }'
panic: malloc, size=18446744071562068026 at -e line 1.

Instead, check for this situation, and croak with an appropriate (new)
diagnostic in the unlikely event that it occurs.

This also involves changing the type of an argument to a public API function:
Perl_share_hek() previously took the key's length as an I32, but that makes
it impossible to detect over-long keys, so it must be SSize_t instead.

From Yves:
We also inject the length test into the PERL_HASH() macro, so that where
the macro is used *before* calling into any of the hv functions we can
avoid hashing a very long string only to throw an exception that it is
too long. Might as well fail fast.

1 files changed, 2 insertions, 2 deletions

diff --git a/proto.h b/proto.h
index b581ffdbaf..e129449a4a 100644
--- a/proto.h
+++ b/proto.h
@@ -2914,7 +2914,7 @@ PERL_CALLCONV void	Perl_set_numeric_standard(pTHX);
 PERL_CALLCONV void	Perl_setdefout(pTHX_ GV* gv);
 #define PERL_ARGS_ASSERT_SETDEFOUT	\
 	assert(gv)
-PERL_CALLCONV HEK*	Perl_share_hek(pTHX_ const char* str, I32 len, U32 hash);
+PERL_CALLCONV HEK*	Perl_share_hek(pTHX_ const char* str, SSize_t len, U32 hash);
 #define PERL_ARGS_ASSERT_SHARE_HEK	\
 	assert(str)
 PERL_CALLCONV void	Perl_sortsv(pTHX_ SV** array, size_t num_elts, SVCOMPARE_t cmp);
@@ -4570,7 +4570,7 @@ STATIC HEK*	S_save_hek_flags(const char *str, I32 len, U32 hash, int flags)
 #define PERL_ARGS_ASSERT_SAVE_HEK_FLAGS	\
 	assert(str)
 
-STATIC HEK*	S_share_hek_flags(pTHX_ const char *str, I32 len, U32 hash, int flags)
+STATIC HEK*	S_share_hek_flags(pTHX_ const char *str, STRLEN len, U32 hash, int flags)
 			__attribute__warn_unused_result__;
 #define PERL_ARGS_ASSERT_SHARE_HEK_FLAGS	\
 	assert(str)