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wip(ref): copy-on-write for sentry_value_t clone #1794

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648f02e
benchmark: scope & value
jpnurmi Jun 4, 2026
2a58348
fix: clone user and fingerprint in scope_apply_to_event
jpnurmi Jun 4, 2026
ec86d1f
ref: copy-on-write for sentry_value_t clone
jpnurmi Mar 4, 2026
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4 changes: 2 additions & 2 deletions src/sentry_scope.c
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Original file line number Diff line number Diff line change
Expand Up @@ -412,10 +412,10 @@ sentry__scope_apply_to_event(const sentry_scope_t *scope,
sentry_value_new_string(options->run->installation_id));
}
} else if (sentry_value_get_length(scope->user) > 0) {
PLACE_VALUE("user", scope->user);
PLACE_CLONED_VALUE("user", scope->user);
}
}
PLACE_VALUE("fingerprint", scope->fingerprint);
PLACE_CLONED_VALUE("fingerprint", scope->fingerprint);
PLACE_STRING("transaction", scope->transaction);
PLACE_VALUE("sdk", scope->client_sdk);

Expand Down
228 changes: 198 additions & 30 deletions src/sentry_value.c
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,7 @@ typedef struct {
sentry_value_t *items;
size_t len;
size_t allocated;
long refcount;
} list_t;

typedef struct {
Expand All @@ -104,6 +105,7 @@ typedef struct {
obj_pair_t *pairs;
size_t len;
size_t allocated;
long refcount;
} obj_t;

static const char *
Expand Down Expand Up @@ -161,33 +163,143 @@ thing_get_type(const thing_t *thing)
}

static void
thing_free(thing_t *thing)
list_free(list_t *list)
{
if (sentry__atomic_fetch_and_add(&list->refcount, -1) != 1) {
return;
}
for (size_t i = 0; i < list->len; i++) {
sentry_value_decref(list->items[i]);
}
sentry_free(list->items);
sentry_free(list);
}

static void
obj_free(obj_t *obj)
{
if (sentry__atomic_fetch_and_add(&obj->refcount, -1) != 1) {
return;
}
for (size_t i = 0; i < obj->len; i++) {
sentry_free(obj->pairs[i].k);
sentry_value_decref(obj->pairs[i].v);
}
sentry_free(obj->pairs);
sentry_free(obj);
}

static bool
thing_detach(thing_t *thing)
{
switch (thing_get_type(thing)) {
case THING_TYPE_LIST: {
list_t *list = thing->payload._ptr;
for (size_t i = 0; i < list->len; i++) {
sentry_value_decref(list->items[i]);
list_t *old = thing->payload._ptr;
if (sentry__atomic_fetch(&old->refcount) <= 1) {
return true;
}
sentry_free(list->items);
sentry_free(list);
break;
list_t *new_list = SENTRY_MAKE(list_t);
if (!new_list) {
return false;
}
new_list->len = old->len;
new_list->allocated = old->len;
new_list->refcount = 1;
if (old->len) {
new_list->items = sentry_malloc(sizeof(sentry_value_t) * old->len);
if (!new_list->items) {
sentry_free(new_list);
return false;
}
memcpy(
new_list->items, old->items, sizeof(sentry_value_t) * old->len);
for (size_t i = 0; i < old->len; i++) {
sentry_value_incref(new_list->items[i]);
}
} else {
new_list->items = NULL;
}
list_free(old);
thing->payload._ptr = new_list;
return true;
}
case THING_TYPE_OBJECT: {
obj_t *obj = thing->payload._ptr;
for (size_t i = 0; i < obj->len; i++) {
sentry_free(obj->pairs[i].k);
sentry_value_decref(obj->pairs[i].v);
obj_t *old = thing->payload._ptr;
if (sentry__atomic_fetch(&old->refcount) <= 1) {
return true;
}
obj_t *new_obj = SENTRY_MAKE(obj_t);
if (!new_obj) {
return false;
}
new_obj->len = old->len;
new_obj->allocated = old->len;
new_obj->refcount = 1;
if (old->len) {
new_obj->pairs = sentry_malloc(sizeof(obj_pair_t) * old->len);
if (!new_obj->pairs) {
sentry_free(new_obj);
return false;
}
for (size_t i = 0; i < old->len; i++) {
new_obj->pairs[i].k = sentry__string_clone(old->pairs[i].k);
new_obj->pairs[i].v = old->pairs[i].v;
sentry_value_incref(new_obj->pairs[i].v);
}
} else {
new_obj->pairs = NULL;
}
sentry_free(obj->pairs);
sentry_free(obj);
obj_free(old);
thing->payload._ptr = new_obj;

@cursor cursor Bot Jun 4, 2026

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Detach ignores clone key failure

Medium Severity

During object copy-on-write in thing_detach, sentry__string_clone results are not checked. If key duplication fails under memory pressure, the new object can retain null keys and is still installed as the live payload.

Fix in Cursor Fix in Web

Reviewed by Cursor Bugbot for commit ec86d1f. Configure here.

return true;
}
default:
return true;
}
}

static sentry_value_t
thing_get_child(const thing_t *thing, size_t i)
{
switch (thing_get_type(thing)) {
case THING_TYPE_LIST:
return ((const list_t *)thing->payload._ptr)->items[i];
case THING_TYPE_OBJECT:
return ((const obj_t *)thing->payload._ptr)->pairs[i].v;
default:
return sentry_value_new_null();
}
}

static void
thing_set_child(thing_t *thing, size_t i, sentry_value_t value)
{
switch (thing_get_type(thing)) {
case THING_TYPE_LIST:
((list_t *)thing->payload._ptr)->items[i] = value;
break;
case THING_TYPE_OBJECT:
((obj_t *)thing->payload._ptr)->pairs[i].v = value;
break;
default:
break;
}
case THING_TYPE_STRING: {
}

static void
thing_free(thing_t *thing)
{
switch (thing_get_type(thing)) {
case THING_TYPE_LIST:
list_free(thing->payload._ptr);
break;
case THING_TYPE_OBJECT:
obj_free(thing->payload._ptr);
break;
case THING_TYPE_STRING:
sentry_free(thing->payload._ptr);
break;
}
}
sentry_free(thing);
}

Expand Down Expand Up @@ -395,6 +507,8 @@ sentry_value_new_list(void)
{
list_t *l = SENTRY_MAKE(list_t);
if (l) {
memset(l, 0, sizeof(list_t));
l->refcount = 1;
sentry_value_t rv = new_thing_value(l, THING_TYPE_LIST);
if (sentry_value_is_null(rv)) {
sentry_free(l);
Expand All @@ -410,6 +524,8 @@ sentry__value_new_list_with_size(size_t size)
{
list_t *l = SENTRY_MAKE(list_t);
if (l) {
memset(l, 0, sizeof(list_t));
l->refcount = 1;
l->allocated = size;
if (size) {
l->items = sentry_malloc(sizeof(sentry_value_t) * size);
Expand All @@ -434,6 +550,8 @@ sentry_value_new_object(void)
{
obj_t *o = SENTRY_MAKE(obj_t);
if (o) {
memset(o, 0, sizeof(obj_t));
o->refcount = 1;
sentry_value_t rv = new_thing_value(o, THING_TYPE_OBJECT);
if (sentry_value_is_null(rv)) {
sentry_free(o);
Expand All @@ -449,6 +567,8 @@ sentry__value_new_object_with_size(size_t size)
{
obj_t *o = SENTRY_MAKE(obj_t);
if (o) {
memset(o, 0, sizeof(obj_t));
o->refcount = 1;
o->allocated = size;
if (size) {
o->pairs = sentry_malloc(sizeof(obj_pair_t) * size);
Expand Down Expand Up @@ -639,7 +759,8 @@ sentry_value_set_by_key_n(
}
sentry_slice_t k_slice = { k, k_len };
thing_t *thing = value_as_unfrozen_thing(value);
if (!thing || thing_get_type(thing) != THING_TYPE_OBJECT) {
if (!thing || thing_get_type(thing) != THING_TYPE_OBJECT
|| !thing_detach(thing)) {
goto fail;
}
obj_t *o = thing->payload._ptr;
Expand Down Expand Up @@ -690,7 +811,8 @@ sentry_value_remove_by_key_n(sentry_value_t value, const char *k, size_t k_len)
}
sentry_slice_t k_slice = { k, k_len };
thing_t *thing = value_as_unfrozen_thing(value);
if (!thing || thing_get_type(thing) != THING_TYPE_OBJECT) {
if (!thing || thing_get_type(thing) != THING_TYPE_OBJECT
|| !thing_detach(thing)) {
return 1;
}
obj_t *o = thing->payload._ptr;
Expand Down Expand Up @@ -722,7 +844,8 @@ int
sentry_value_append(sentry_value_t value, sentry_value_t v)
{
thing_t *thing = value_as_unfrozen_thing(value);
if (!thing || thing_get_type(thing) != THING_TYPE_LIST) {
if (!thing || thing_get_type(thing) != THING_TYPE_LIST
|| !thing_detach(thing)) {
goto fail;
}

Expand Down Expand Up @@ -791,6 +914,39 @@ sentry__value_stringify(sentry_value_t value)
#undef STRINGIFY_NUMERIC
}

static bool
value_is_container(sentry_value_t value)
{
const thing_t *thing = value_as_thing(value);
if (!thing) {
return false;
}
int type = thing_get_type(thing);
return type == THING_TYPE_LIST || type == THING_TYPE_OBJECT;
}

static bool
thing_clone_children(thing_t *thing, size_t len)
{
bool detached = false;
for (size_t i = 0; i < len; i++) {
sentry_value_t child = thing_get_child(thing, i);
if (!value_is_container(child)) {
continue;
}
if (!detached) {
if (!thing_detach(thing)) {
return false;
}
detached = true;
}
sentry_value_t cloned = sentry__value_clone(child);
sentry_value_decref(child);
thing_set_child(thing, i, cloned);
}
return true;

@cursor cursor Bot Jun 4, 2026

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Nested clone failure ignored

Medium Severity

In thing_clone_children, when sentry__value_clone fails for a nested container it still returns success after sentry_value_decref and storing a null child. The outer sentry__value_clone then returns a usable-looking clone with missing nested data instead of failing entirely.

Fix in Cursor Fix in Web

Reviewed by Cursor Bugbot for commit ec86d1f. Configure here.

}

sentry_value_t
sentry__value_clone(sentry_value_t value)
{
Expand All @@ -800,20 +956,30 @@ sentry__value_clone(sentry_value_t value)
}
switch (thing_get_type(thing)) {
case THING_TYPE_LIST: {
const list_t *list = thing->payload._ptr;
sentry_value_t rv = sentry__value_new_list_with_size(list->len);
for (size_t i = 0; i < list->len; i++) {
sentry_value_incref(list->items[i]);
sentry_value_append(rv, list->items[i]);
list_t *list = thing->payload._ptr;
sentry__atomic_fetch_and_add(&list->refcount, 1);
sentry_value_t rv = new_thing_value(list, THING_TYPE_LIST);
if (sentry_value_is_null(rv)) {
list_free(list);
return rv;
}
if (!thing_clone_children(value_as_thing(rv), list->len)) {
sentry_value_decref(rv);
return sentry_value_new_null();
}
return rv;
}
case THING_TYPE_OBJECT: {
const obj_t *obj = thing->payload._ptr;
sentry_value_t rv = sentry__value_new_object_with_size(obj->len);
for (size_t i = 0; i < obj->len; i++) {
sentry_value_incref(obj->pairs[i].v);
sentry_value_set_by_key(rv, obj->pairs[i].k, obj->pairs[i].v);
obj_t *obj = thing->payload._ptr;
sentry__atomic_fetch_and_add(&obj->refcount, 1);
sentry_value_t rv = new_thing_value(obj, THING_TYPE_OBJECT);
if (sentry_value_is_null(rv)) {
obj_free(obj);
return rv;
}
if (!thing_clone_children(value_as_thing(rv), obj->len)) {
sentry_value_decref(rv);
return sentry_value_new_null();
}
return rv;
}
Expand All @@ -832,7 +998,8 @@ int
sentry_value_set_by_index(sentry_value_t value, size_t index, sentry_value_t v)
{
thing_t *thing = value_as_unfrozen_thing(value);
if (!thing || thing_get_type(thing) != THING_TYPE_LIST) {
if (!thing || thing_get_type(thing) != THING_TYPE_LIST
|| !thing_detach(thing)) {
goto fail;
}

Expand Down Expand Up @@ -862,7 +1029,8 @@ int
sentry_value_remove_by_index(sentry_value_t value, size_t index)
{
thing_t *thing = value_as_unfrozen_thing(value);
if (!thing || thing_get_type(thing) != THING_TYPE_LIST) {
if (!thing || thing_get_type(thing) != THING_TYPE_LIST
|| !thing_detach(thing)) {
return 1;
}

Expand Down
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