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libexpr: Do not overflow heap buffer when there are too many formal arguments

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3a3c062982 introduced a buffer overflow for the
case when there are more than 65535 formal arguments. It is a perfectly reasonable
limitation, but we *must* not crash, corrupt memory or otherwise crash the process.

Add a test for the graceful behavior and switch to using an explicit uninitialized_copy_n
to further guard against buffer overflows.
This commit is contained in:
Sergei Zimmerman 2025-11-01 12:53:53 +03:00
parent 9d1907fff7
commit 134613e885
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3 changed files with 40 additions and 8 deletions
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20
src/libexpr-tests/trivial.cc
View file

@ -1,4 +1,5 @@
#include "nix/expr/tests/libexpr.hh"
#include "nix/util/tests/gmock-matchers.hh"
namespace nix {
// Testing of trivial expressions
@ -160,7 +161,8 @@ TEST_F(TrivialExpressionTest, assertPassed)
ASSERT_THAT(v, IsIntEq(123));
}
class AttrSetMergeTrvialExpressionTest : public TrivialExpressionTest, public testing::WithParamInterface<const char *>
class AttrSetMergeTrvialExpressionTest : public TrivialExpressionTest,
public ::testing::WithParamInterface<const char *>
{};
TEST_P(AttrSetMergeTrvialExpressionTest, attrsetMergeLazy)
@ -196,7 +198,7 @@ TEST_P(AttrSetMergeTrvialExpressionTest, attrsetMergeLazy)
INSTANTIATE_TEST_SUITE_P(
attrsetMergeLazy,
AttrSetMergeTrvialExpressionTest,
testing::Values("{ a.b = 1; a.c = 2; }", "{ a = { b = 1; }; a = { c = 2; }; }"));
::testing::Values("{ a.b = 1; a.c = 2; }", "{ a = { b = 1; }; a = { c = 2; }; }"));
// The following macros ultimately define 48 tests (16 variations on three
// templates). Each template tests an expression that can be written in 2^4
@ -339,4 +341,18 @@ TEST_F(TrivialExpressionTest, orCantBeUsed)
{
ASSERT_THROW(eval("let or = 1; in or"), Error);
}
TEST_F(TrivialExpressionTest, tooManyFormals)
{
std::string expr = "let f = { ";
for (uint32_t i = 0; i <= std::numeric_limits<uint16_t>::max(); ++i) {
expr += fmt("arg%d, ", i);
}
expr += " }: 0 in; f {}";
ASSERT_THAT(
[&]() { eval(expr); },
::testing::ThrowsMessage<Error>(::nix::testing::HasSubstrIgnoreANSIMatcher(
"too many formal arguments, implementation supports at most 65535")));
}
} /* namespace nix */