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/erl_bits.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'erts/emulator/beam/erl_bits.c') diff --git a/erts/emulator/beam/erl_bits.c b/erts/emulator/beam/erl_bits.c index 73765772c8..642f56a15e 100644 --- a/erts/emulator/beam/erl_bits.c +++ b/erts/emulator/beam/erl_bits.c @@ -403,7 +403,9 @@ erts_bs_get_integer_2(Process *p, Uint num_bits, unsigned flags, ErlBinMatchBuff words_needed = 1+WSIZE(bytes); hp = HeapOnlyAlloc(p, words_needed); res = bytes_to_big(LSB, bytes, sgn, hp); - if (is_small(res)) { + if (is_nil(res)) { + res = THE_NON_VALUE; + } else if (is_small(res)) { p->htop = hp; } else if ((actual = bignum_header_arity(*hp)+1) < words_needed) { p->htop = hp + actual; -- cgit v1.2.3