Set ErlNifEntry.min_erts to a placeholder value (#703)

This value was introduced with NIF version 2.14 (so, OTP-21, erts-10.0).

Us leaving it unassigned and defaulting to NIF version 2.15 means the OTP is currently
always putting a random pointer into the respective field here:

https://github.com/erlang/otp/blob/ae81b2f6ff2d541c01242f12cdbd5238aa4b26bd/erts/emulator/beam/erl_nif.c#L4581-L4585

It is used if one tries to load a NIF library that was compiled for a
newer NIF version to display a debug message, at which point it would
perform an out-of-bounds read.

As we currently default to NIF v2.15 (OTP-22) and only have features up
to 2.16 (OTP-24), there are probably very few cases of this actually
occurring in the wild.

Author: filmor

rustler/src/codegen_runtime.rs

@@ -140,3 +140,15 @@ where
         }
     }
 }
+
+pub const fn min_erts() -> &'static [u8] {
+    if cfg!(feature = "nif_version_2_17") {
+        b"OTP-26.0\0"
+    } else if cfg!(feature = "nif_version_2_16") {
+        b"OTP-24.0\0"
+    } else if cfg!(feature = "nif_version_2_15") {
+        b"OTP-22.0\0"
+    } else {
+        b"OTP-21.0\0"
+    }
+}

rustler/src/sys/types.rs

@@ -85,6 +85,7 @@ pub struct ErlNifEntry {
     pub vm_variant: *const c_char,
     pub options: c_uint,                      // added in 2.7
     pub sizeof_ErlNifResourceTypeInit: usize, // added in 2.12
+    pub min_erts: *const c_char,              // added in 2.14
 }
 
 pub const ERL_NIF_DIRTY_NIF_OPTION: c_uint = 1;

rustler_codegen/src/init.rs

@@ -125,6 +125,7 @@ impl From<InitMacroInput> for proc_macro2::TokenStream {
                 vm_variant: b"beam.vanilla\0".as_ptr() as *const rustler::codegen_runtime::c_char,
                 options: 0,
                 sizeof_ErlNifResourceTypeInit: rustler::codegen_runtime::get_nif_resource_type_init_size(),
+                min_erts: rustler::codegen_runtime::min_erts().as_ptr() as *const rustler::codegen_runtime::c_char,
             };
 
             unsafe {