From 7e147a05683c709128b6777d0c360fcde067f567 Mon Sep 17 00:00:00 2001 From: Mikael Pettersson Date: Wed, 4 Feb 2015 20:27:37 +0100 Subject: don't create oversize bignums in binary matching Bignums are artifically restricted in size. Arithmetic and logical operations check the sizes of resulting bignums, and turn oversize results into system_limit exceptions. However, this check is not performed when bignums are constructed by binary matching. The consequence is that such matchings can construct oversize bignums that satisfy is_integer/1 yet don't work. Performing arithmetic such as Term - 0 fails with a system_limit exception. Worse, performing a logical operation such as Term band Term results in []. The latter occurs because the size checking (e.g. in erts_band()) is a simple ASSERT(is_not_nil(...)) on the result of the bignum operation, which internally is [] (NIL) in the case of oversize results. However, ASSERT is a no-op in release builds, so the error goes unnoticed and [] is returned as the result of the band/2. This patch addresses this by preventing oversize bignums from entering the VM via binary matching: - the internal bytes_to_big() procedure is augmented to return NIL for oversize results, just like big_norm() - callers of bytes_to_big() are augmented to check for NIL returns and signal errors in those cases - erts_bs_get_integer_2() can only fail with badmatch, so that is the Erlang-level result of oversize bignums from binary matches - big_SUITE.erl is extended with a test case that fails without this fix (no error signalled) and passes with it (badmatch occurs) Credit goes to Nico Kruber for the initial bug report. --- erts/emulator/beam/external.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'erts/emulator/beam/external.c') diff --git a/erts/emulator/beam/external.c b/erts/emulator/beam/external.c index 9b9b4b2a62..45d1f7514e 100644 --- a/erts/emulator/beam/external.c +++ b/erts/emulator/beam/external.c @@ -3056,6 +3056,8 @@ dec_term(ErtsDistExternal *edep, Eterm** hpp, byte* ep, ErlOffHeap* off_heap, big = make_small(0); } else { big = bytes_to_big(first, n, neg, hp); + if (is_nil(big)) + goto error; if (is_big(big)) { hp += big_arity(big) + 1; } -- cgit v1.2.3