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Harden mutable-to-immutable copy against overflow, malformed structures, and deep recursion #261

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Harden mutable-to-immutable copy against overflow, malformed structures, and deep recursion #261

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4001079
Harden mutable-to-immutable copy against overflow, malformed structur…
rootvector2 Apr 12, 2026
c396bdb
Align imut copy hardening with maintainer guidance
rootvector2 Apr 13, 2026
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79 changes: 67 additions & 12 deletions src/yyjson.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2137,6 +2137,11 @@ static_inline bool size_add_is_overflow(usize size, usize add) {
return size > (size + add);
}

/** Returns whether the size is overflow after multiplication. */
static_inline bool size_mul_is_overflow(usize size, usize mul) {
return mul != 0 && size > USIZE_MAX / mul;
}

/** Returns whether the size is power of 2 (size should not be 0). */
static_inline bool size_is_pow2(usize size) {
return (size & (size - 1)) == 0;
Expand Down Expand Up @@ -2804,62 +2809,103 @@ yyjson_mut_val *yyjson_mut_val_mut_copy(yyjson_mut_doc *doc,
return NULL;
}

/* Count the number of values and the total length of the strings. */
static void yyjson_mut_stat(const yyjson_mut_val *val,
/* Count value and string pool sizes; return false on overflow. */
static bool yyjson_mut_stat(const yyjson_mut_val *val,
usize *val_sum, usize *str_sum) {
yyjson_type type = unsafe_yyjson_get_type(val);
yyjson_type type;

type = unsafe_yyjson_get_type(val);
if (unlikely(size_add_is_overflow(*val_sum, 1))) return false;
*val_sum += 1;

if (type == YYJSON_TYPE_ARR || type == YYJSON_TYPE_OBJ) {
yyjson_mut_val *child = (yyjson_mut_val *)val->uni.ptr;
usize len = unsafe_yyjson_get_len(val), i;
len <<= (u8)(type == YYJSON_TYPE_OBJ);

if (type == YYJSON_TYPE_OBJ) {
if (unlikely(len > USIZE_MAX / 2)) return false;
len <<= 1;
}

if (unlikely(size_add_is_overflow(*val_sum, len))) return false;
*val_sum += len;

for (i = 0; i < len; i++) {
yyjson_type stype = unsafe_yyjson_get_type(child);
if (stype == YYJSON_TYPE_STR || stype == YYJSON_TYPE_RAW) {
*str_sum += unsafe_yyjson_get_len(child) + 1;
usize str_len = unsafe_yyjson_get_len(child);
if (unlikely(size_add_is_overflow(str_len, 1) ||
size_add_is_overflow(*str_sum, str_len + 1))) {
return false;
}
*str_sum += str_len + 1;
} else if (stype == YYJSON_TYPE_ARR || stype == YYJSON_TYPE_OBJ) {
yyjson_mut_stat(child, val_sum, str_sum);
if (unlikely(!yyjson_mut_stat(child, val_sum, str_sum))) {
return false;
}
*val_sum -= 1;
}
child = child->next;
}
} else if (type == YYJSON_TYPE_STR || type == YYJSON_TYPE_RAW) {
*str_sum += unsafe_yyjson_get_len(val) + 1;
usize len = unsafe_yyjson_get_len(val);
if (unlikely(size_add_is_overflow(len, 1) ||
size_add_is_overflow(*str_sum, len + 1))) {
return false;
}
*str_sum += len + 1;
}

return true;
}

/* Copy mutable values to immutable value pool. */
static usize yyjson_imut_copy(yyjson_val **val_ptr, char **buf_ptr,
const yyjson_mut_val *mval) {
yyjson_val *val = *val_ptr;
yyjson_type type = unsafe_yyjson_get_type(mval);
yyjson_type type;

type = unsafe_yyjson_get_type(mval);

if (type == YYJSON_TYPE_ARR || type == YYJSON_TYPE_OBJ) {
yyjson_mut_val *child = (yyjson_mut_val *)mval->uni.ptr;
usize len = unsafe_yyjson_get_len(mval), i;
usize val_sum = 1;

if (type == YYJSON_TYPE_OBJ) {
if (unlikely(len > USIZE_MAX / 2)) return 0;
if (len) child = child->next->next;
len <<= 1;
} else {
if (len) child = child->next;
}

*val_ptr = val + 1;
for (i = 0; i < len; i++) {
val_sum += yyjson_imut_copy(val_ptr, buf_ptr, child);
usize child_sum = yyjson_imut_copy(val_ptr, buf_ptr, child);
if (unlikely(child_sum == 0 ||
size_add_is_overflow(val_sum, child_sum))) {
return 0;
}
val_sum += child_sum;
child = child->next;
}
val->tag = mval->tag;
if (unlikely(size_mul_is_overflow(val_sum, sizeof(yyjson_val)))) {
return 0;
}
val->uni.ofs = val_sum * sizeof(yyjson_val);
return val_sum;
} else if (type == YYJSON_TYPE_STR || type == YYJSON_TYPE_RAW) {
char *buf = *buf_ptr;
usize len = unsafe_yyjson_get_len(mval);

memcpy((void *)buf, (const void *)mval->uni.str, len);
buf[len] = '\0';
val->tag = mval->tag;
val->uni.str = buf;
*val_ptr = val + 1;
if (unlikely(size_add_is_overflow(len, 1))) return 0;
*buf_ptr = buf + len + 1;
return 1;
} else {
Expand All @@ -2878,7 +2924,7 @@ yyjson_doc *yyjson_mut_doc_imut_copy(const yyjson_mut_doc *mdoc,

yyjson_doc *yyjson_mut_val_imut_copy(const yyjson_mut_val *mval,
const yyjson_alc *alc) {
usize val_num = 0, str_sum = 0, hdr_size, buf_size;
usize val_num = 0, str_sum = 0, hdr_size, val_size, buf_size;
yyjson_doc *doc = NULL;
yyjson_val *val_hdr = NULL;

Expand All @@ -2889,11 +2935,15 @@ yyjson_doc *yyjson_mut_val_imut_copy(const yyjson_mut_val *mval,
if (!alc) alc = &YYJSON_DEFAULT_ALC;

/* traverse the input value to get pool size */
yyjson_mut_stat(mval, &val_num, &str_sum);
if (unlikely(!yyjson_mut_stat(mval, &val_num, &str_sum))) return NULL;
if (unlikely(size_add_is_overflow(str_sum, 1))) return NULL;

/* create doc and val pool */
hdr_size = size_align_up(sizeof(yyjson_doc), sizeof(yyjson_val));
buf_size = hdr_size + val_num * sizeof(yyjson_val);
if (unlikely(size_mul_is_overflow(val_num, sizeof(yyjson_val)))) return NULL;
val_size = val_num * sizeof(yyjson_val);
if (unlikely(size_add_is_overflow(hdr_size, val_size))) return NULL;
buf_size = hdr_size + val_size;
doc = (yyjson_doc *)alc->malloc(alc->ctx, buf_size);
if (!doc) return NULL;
memset(doc, 0, sizeof(yyjson_doc));
Expand All @@ -2913,6 +2963,11 @@ yyjson_doc *yyjson_mut_val_imut_copy(const yyjson_mut_val *mval,

/* copy vals and strs */
doc->val_read = yyjson_imut_copy(&val_hdr, &str_hdr, mval);
if (unlikely(doc->val_read == 0)) {
if (doc->str_pool) alc->free(alc->ctx, doc->str_pool);
alc->free(alc->ctx, (void *)doc);
return NULL;
}
doc->dat_read = str_sum + 1;
return doc;
}
Expand Down