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fix(json): reject malformed hex input

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Reject odd-length and non-hex strings before decoding them.

Tested: 1796 ASan/UBSan tests in amalgamated and unamalgamated builds
This commit is contained in:
94xhn committed 2026-07-16 08:33:06 +08:00
1 parent bc69625a5e
commit dc52d8b1dc
5 files changed
+29 -13
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mongoose.c
+8 -5
View File
@@ -5078,15 +5078,18 @@ char *mg_json_get_b64(struct mg_str json, const char *path, int *slen) {
char *mg_json_get_hex(struct mg_str json, const char *path, int *slen) {
char *result = NULL;
int len = 0, off = mg_json_get(json, path, &len);
if (off >= 0 && json.buf[off] == '"' && len > 1 &&
if (off >= 0 && json.buf[off] == '"' && len > 1 && (len - 2) % 2 == 0 &&
(result = (char *) mg_calloc(1, (size_t) len / 2)) != NULL) {
int i;
for (i = 0; i < len - 2; i += 2) {
mg_str_to_num(mg_str_n(json.buf + off + 1 + i, 2), 16, &result[i >> 1],
sizeof(uint8_t));
if (!mg_str_to_num(mg_str_n(json.buf + off + 1 + i, 2), 16,
&result[i >> 1], sizeof(uint8_t))) break;
}
if (i < len - 2) mg_free(result), result = NULL;
if (result != NULL) {
result[len / 2 - 1] = '\0';
if (slen != NULL) *slen = len / 2 - 1;
}
result[len / 2 - 1] = '\0';
if (slen != NULL) *slen = len / 2 - 1;
}
return result;
}
mongoose.h
+1 -1
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@@ -4104,7 +4104,7 @@ char *mg_json_get_str(struct mg_str json, const char *path);
// Decodes a hex-encoded JSON string at path into a heap-allocated byte array.
// Sets *len to the decoded byte count. Caller must mg_free() the result.
// Returns NULL if not found or not a string.
// Returns NULL if not found, not a string, or not valid hexadecimal.
char *mg_json_get_hex(struct mg_str json, const char *path, int *len);
// Decodes a base64-encoded JSON string at path into a heap-allocated byte
src/json.c
+8 -5
View File
@@ -363,15 +363,18 @@ char *mg_json_get_b64(struct mg_str json, const char *path, int *slen) {
char *mg_json_get_hex(struct mg_str json, const char *path, int *slen) {
char *result = NULL;
int len = 0, off = mg_json_get(json, path, &len);
if (off >= 0 && json.buf[off] == '"' && len > 1 &&
if (off >= 0 && json.buf[off] == '"' && len > 1 && (len - 2) % 2 == 0 &&
(result = (char *) mg_calloc(1, (size_t) len / 2)) != NULL) {
int i;
for (i = 0; i < len - 2; i += 2) {
mg_str_to_num(mg_str_n(json.buf + off + 1 + i, 2), 16, &result[i >> 1],
sizeof(uint8_t));
if (!mg_str_to_num(mg_str_n(json.buf + off + 1 + i, 2), 16,
&result[i >> 1], sizeof(uint8_t))) break;
}
if (i < len - 2) mg_free(result), result = NULL;
if (result != NULL) {
result[len / 2 - 1] = '\0';
if (slen != NULL) *slen = len / 2 - 1;
}
result[len / 2 - 1] = '\0';
if (slen != NULL) *slen = len / 2 - 1;
}
return result;
}
src/json.h
+1 -1
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@@ -57,7 +57,7 @@ char *mg_json_get_str(struct mg_str json, const char *path);
// Decodes a hex-encoded JSON string at path into a heap-allocated byte array.
// Sets *len to the decoded byte count. Caller must mg_free() the result.
// Returns NULL if not found or not a string.
// Returns NULL if not found, not a string, or not valid hexadecimal.
char *mg_json_get_hex(struct mg_str json, const char *path, int *len);
// Decodes a base64-encoded JSON string at path into a heap-allocated byte
test/unit_test.c
+11 -1
View File
@@ -3741,13 +3741,23 @@ static void test_json(void) {
ASSERT(b == true);
ASSERT(mg_json_get(json, "$.b[2]", &len) < 0);
json = mg_str("[\"YWJj\", \"0100026869\"]");
json = mg_str("[\"YWJj\", \"0100026869\", \"\", \"abc\", \"0g\"]");
ASSERT((str = mg_json_get_b64(json, "$[0]", &len)) != NULL);
ASSERT(len == 3 && memcmp(str, "abc", (size_t) len) == 0);
mg_free(str);
ASSERT((str = mg_json_get_hex(json, "$[1]", &len)) != NULL);
ASSERT(len == 5 && memcmp(str, "\x01\x00\x02hi", (size_t) len) == 0);
mg_free(str);
ASSERT((str = mg_json_get_hex(json, "$[2]", &len)) != NULL);
ASSERT(len == 0 && str[0] == '\0');
mg_free(str);
len = 42;
str = mg_json_get_hex(json, "$[3]", &len);
ASSERT(str == NULL && len == 42);
mg_free(str);
str = mg_json_get_hex(json, "$[4]", &len);
ASSERT(str == NULL && len == 42);
mg_free(str);
json = mg_str("{\"a\":[1,2,3], \"ab\": 2}");
ASSERT(mg_json_get_long(json, "$.a[0]", -42) == 1);