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binpac: Fix signed integer overflow in array bounds checks

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Array lengths use signed integer storage, so multiplication of that
by the element size for purpose of bounds checking against available
data may produce a signed integer overlow, which is undefined behavior.
This commit is contained in:
Jon Siwek 2019-06-26 23:31:59 -07:00 • committed by Tim Wojtulewicz
parent 7632c69566
commit ef933c9e76
1 changed files with 22 additions and 9 deletions
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31
tools/binpac/src/pac_array.cc
View file

@ -292,7 +292,7 @@ void ArrayType::GenArrayLength(Output *out_cc, Env *env, const DataPtr& data)
out_cc->println("}");
out_cc->dec_indent();
string array_size;
int element_size;
if ( elemtype_->StaticSize(env) == -1 )
{
@ -307,7 +307,7 @@ void ArrayType::GenArrayLength(Output *out_cc, Env *env, const DataPtr& data)
// buffer.
out_cc->println("// Check array element quantity: %s",
data_id_str_.c_str());
array_size = strfmt("(%s)", env->RValue(arraylength_var()));
element_size = 1;
}
else
{
@ -315,21 +315,34 @@ void ArrayType::GenArrayLength(Output *out_cc, Env *env, const DataPtr& data)
out_cc->println("// Check bounds for static-size array: %s",
data_id_str_.c_str());
elemtype_->SetBoundaryChecked();
array_size = strfmt("((%d) * (%s))",
elemtype_->StaticSize(env),
env->RValue(arraylength_var()));
element_size = elemtype_->StaticSize(env);
if ( element_size == 0 )
{
// If we know we have an array of empty elements, probably
// better to structure the parser as just a single empty
// field to avoid DoS vulnerability of allocating
// arbitrary number of empty records (i.e. cheap for them,
// but costly for us unless we have special optimization
// for this scenario to forgo the usual allocation).
throw Exception(this, "using an array of known-to-be-empty elements is possibly a bad idea");
}
}
const char* array_ptr_expr = data.ptr_expr();
string max_elements_available = strfmt("((%s - %s) / %d)",
env->RValue(end_of_data),
array_ptr_expr,
element_size);
out_cc->println("if ( %s + %s > %s || %s + %s < %s )",
array_ptr_expr, array_size.c_str(), env->RValue(end_of_data),
array_ptr_expr, array_size.c_str(), array_ptr_expr);
out_cc->println("if ( %s > %s )",
env->RValue(arraylength_var()),
max_elements_available.c_str());
out_cc->inc_indent();
out_cc->println("throw binpac::ExceptionOutOfBound(\"%s\",",
data_id_str_.c_str());
out_cc->println(" %s, (%s) - (%s));",
array_size.c_str(),
env->RValue(arraylength_var()),
env->RValue(end_of_data),
array_ptr_expr);
out_cc->dec_indent();