Fix out of bounds write in array deserialization

The array was allocated based on the serialized `elsize` of the array,
however, unions get an extra selector array after the regular storage
which was not allocated (because we didn't know it was gonna be a union
array at the time when we allocated it). According to
a48eeef we cannot look at the element
type to allocate the array, so we need to serialize a bit to indicate
that we will have a union array.

Fixes #28998

src/array.c

@@ -53,7 +53,7 @@ size_t jl_arr_xtralloc_limit = 0;
 #define MAXINTVAL (((size_t)-1)>>1)
 
 static jl_array_t *_new_array_(jl_value_t *atype, uint32_t ndims, size_t *dims,
-                               int isunboxed, int elsz)
+                               int isunboxed, int isunion, int elsz)
 {
     jl_ptls_t ptls = jl_get_ptls_states();
     size_t i, tot, nel=1;
@@ -67,7 +67,7 @@ static jl_array_t *_new_array_(jl_value_t *atype, uint32_t ndims, size_t *dims,
             jl_error("invalid Array dimensions");
         nel = prod;
     }
-    int isunion = atype != NULL && jl_is_uniontype(jl_tparam0(atype));
+    assert(atype == NULL || isunion == jl_is_uniontype(jl_tparam0(atype)));
     if (isunboxed) {
         wideint_t prod = (wideint_t)elsz * (wideint_t)nel;
         if (prod > (wideint_t) MAXINTVAL)
@@ -149,18 +149,19 @@ static inline jl_array_t *_new_array(jl_value_t *atype, uint32_t ndims, size_t *
     jl_value_t *eltype = jl_tparam0(atype);
     size_t elsz = 0, al = 0;
     int isunboxed = jl_islayout_inline(eltype, &elsz, &al);
+    int isunion = jl_is_uniontype(eltype);
     if (!isunboxed) {
         elsz = sizeof(void*);
         al = elsz;
     }
 
-    return _new_array_(atype, ndims, dims, isunboxed, elsz);
+    return _new_array_(atype, ndims, dims, isunboxed, isunion, elsz);
 }
 
 jl_array_t *jl_new_array_for_deserialization(jl_value_t *atype, uint32_t ndims, size_t *dims,
-                                             int isunboxed, int elsz)
+                                             int isunboxed, int isunion, int elsz)
 {
-    return _new_array_(atype, ndims, dims, isunboxed, elsz);
+    return _new_array_(atype, ndims, dims, isunboxed, isunion, elsz);
 }
 
 #ifndef JL_NDEBUG
@@ -1115,8 +1116,10 @@ JL_DLLEXPORT jl_array_t *jl_array_copy(jl_array_t *ary)
 {
     size_t elsz = ary->elsize;
     size_t len = jl_array_len(ary);
+    int isunion = jl_is_uniontype(jl_tparam0(jl_typeof(ary)));
     jl_array_t *new_ary = _new_array_(jl_typeof(ary), jl_array_ndims(ary),
-                                      &ary->nrows, !ary->flags.ptrarray, elsz);
+                                      &ary->nrows, !ary->flags.ptrarray,
+                                      isunion, elsz);
     memcpy(new_ary->data, ary->data, len * elsz);
     // ensure isbits union arrays copy their selector bytes correctly
     if (jl_array_isbitsunion(ary))

src/dump.c

@@ -640,14 +640,15 @@ static void jl_serialize_value_(jl_serializer_state *s, jl_value_t *v, int as_li
     }
     else if (jl_is_array(v)) {
         jl_array_t *ar = (jl_array_t*)v;
-        if (ar->flags.ndims == 1 && ar->elsize < 128) {
+        int isunion = jl_is_uniontype(jl_tparam0(jl_typeof(ar)));
+        if (ar->flags.ndims == 1 && ar->elsize <= 0x3f) {
             write_uint8(s->s, TAG_ARRAY1D);
-            write_uint8(s->s, (ar->flags.ptrarray<<7) | (ar->elsize & 0x7f));
+            write_uint8(s->s, (ar->flags.ptrarray<<7) | (isunion << 6) | (ar->elsize & 0x3f));
         }
         else {
             write_uint8(s->s, TAG_ARRAY);
             write_uint16(s->s, ar->flags.ndims);
-            write_uint16(s->s, (ar->flags.ptrarray<<15) | (ar->elsize & 0x7fff));
+            write_uint16(s->s, (ar->flags.ptrarray << 15) | (isunion << 14) | (ar->elsize & 0x3fff));
         }
         for (i = 0; i < ar->flags.ndims; i++)
             jl_serialize_value(s, jl_box_long(jl_array_dim(ar,i)));
@@ -1211,7 +1212,7 @@ static void write_mod_list(ios_t *s, jl_array_t *a)
 }
 
 // "magic" string and version header of .ji file
-static const int JI_FORMAT_VERSION = 6;
+static const int JI_FORMAT_VERSION = 7;
 static const char JI_MAGIC[] = "\373jli\r\n\032\n"; // based on PNG signature
 static const uint16_t BOM = 0xFEFF; // byte-order marker
 static void write_header(ios_t *s)
@@ -1496,18 +1497,20 @@ static jl_value_t *jl_deserialize_value_array(jl_serializer_state *s, uint8_t ta
 {
     int usetable = (s->mode != MODE_IR);
     int16_t i, ndims;
-    int isunboxed, elsize;
+    int isunboxed, isunion, elsize;
     if (tag == TAG_ARRAY1D) {
         ndims = 1;
         elsize = read_uint8(s->s);
         isunboxed = !(elsize >> 7);
-        elsize = elsize & 0x7f;
+        isunion = elsize >> 6;
+        elsize = elsize & 0x3f;
     }
     else {
         ndims = read_uint16(s->s);
         elsize = read_uint16(s->s);
         isunboxed = !(elsize >> 15);
-        elsize = elsize & 0x7fff;
+        isunion = elsize >> 14;
+        elsize = elsize & 0x3fff;
     }
     uintptr_t pos = backref_list.len;
     if (usetable)
@@ -1516,7 +1519,8 @@ static jl_value_t *jl_deserialize_value_array(jl_serializer_state *s, uint8_t ta
     for (i = 0; i < ndims; i++) {
         dims[i] = jl_unbox_long(jl_deserialize_value(s, NULL));
     }
-    jl_array_t *a = jl_new_array_for_deserialization((jl_value_t*)NULL, ndims, dims, isunboxed, elsize);
+    jl_array_t *a = jl_new_array_for_deserialization(
+            (jl_value_t*)NULL, ndims, dims, isunboxed, isunion, elsize);
     if (usetable)
         backref_list.items[pos] = a;
     jl_value_t *aty = jl_deserialize_value(s, &jl_astaggedvalue(a)->type);

src/julia_internal.h

@@ -463,7 +463,7 @@ JL_DLLEXPORT jl_value_t *jl_argument_datatype(jl_value_t *argt JL_PROPAGATES_ROO
 jl_value_t *jl_nth_slot_type(jl_value_t *sig JL_PROPAGATES_ROOT, size_t i) JL_NOTSAFEPOINT;
 void jl_compute_field_offsets(jl_datatype_t *st);
 jl_array_t *jl_new_array_for_deserialization(jl_value_t *atype, uint32_t ndims, size_t *dims,
-                                             int isunboxed, int elsz);
+                                             int isunboxed, int isunion, int elsz);
 void jl_module_run_initializer(jl_module_t *m);
 jl_binding_t *jl_get_module_binding(jl_module_t *m JL_PROPAGATES_ROOT, jl_sym_t *var) JL_NOTSAFEPOINT;
 extern jl_array_t *jl_module_init_order JL_GLOBALLY_ROOTED;

test/precompile.jl

@@ -136,6 +136,12 @@ try
               const x28297 = Result(missing)
 
 
+              # issue #28998
+              const x28998 = [missing, 2, missing, 6, missing,
+                              missing, missing, missing,
+                              missing, missing, missing,
+                              missing, missing, 6]
+
               let some_method = which(Base.include, (String,))
                     # global const some_method // FIXME: support for serializing a direct reference to an external Method not implemented
                   global const some_linfo =
@@ -180,6 +186,8 @@ try
         @test Foo.abigint_x::BigInt + 1 == big"125"
 
         @test Foo.x28297.result === missing
+
+        @test Foo.x28998[end] == 6
     end
 
     cachedir = joinpath(dir, "compiled", "v$(VERSION.major).$(VERSION.minor)")