Bug 23530 – casting immutable away allowed in safe

The following code compiles and runs without crash with DMD 2.100.2, flags -preview=dip1000: ------ @safe void main() { immutable int x = 5; //alternatively const auto a = &x; auto b = &cast() x; assert(a == b); //passes *b = 3; //undefined behaviour } ------ This is a major hole in memory safety, so I'm assigning severity to critical.

dip1000 is not needed to reproduce this: @safe void main() { immutable int x = 5; //alternatively const int* b = &(cast()x); } This used to fail compilation with a wrong error message: Error: `cast(int)x` is not an lvalue and cannot be modified. So I assume that at some point it wasn't possible to take the address of a cast. When safe was implemented they probably took this into account and later on when the cast was allowed someone probably forgot to update the safety check.

@RazvanN7 created dlang/dmd pull request #14668 "Fix Issue 23530 - casting immutable away allowed in safe" fixing this issue: - Fix Issue 23530 - casting immutable away allowed in safe https://github.com/dlang/dmd/pull/14668

@ntrel created dlang/dmd pull request #15597 "Add CastExp.toLvalue obsolete warning if implicit pointer conversion would fail" fixing this issue: - Add CastExp.toLvalue -wo warning if implicit pointer conv would fail From https://dlang.org/spec/expression.html#.define-lvalue > The following expressions, and no others, are called lvalue expressions or lvalues ... > cast(U) expressions applied to lvalues of type T when T* is implicitly convertible to U*; > cast() and cast(qualifier list) when applied to an lvalue. The first rule was not enforced by dmd. The second rule contradicts the point of the first rule. It should be updated to work in the same way. Fixes Issue 23530 - casting immutable away allowed in safe. https://github.com/dlang/dmd/pull/15597

@ntrel updated dlang/dmd pull request #16315 "Fix Bugzilla 24434 - Casting away const with cast() is not a @safe lv…" fixing this issue: - Workaround for safe append Fixes Bugzilla 23530 - casting immutable away allowed in safe. https://github.com/dlang/dmd/pull/16315

dlang/dmd pull request #16315 "Fix Bugzilla 24434 - Casting away const with cast() is not a @safe lv…" was merged into master: - c2eac7ce389eb174cfbb96e66ab4fddb1b48a4b2 by Nick Treleaven: Workaround for safe append Fixes Bugzilla 23530 - casting immutable away allowed in safe. https://github.com/dlang/dmd/pull/16315