Guard deep structural equality and comparison recursion (#3539)

jv_equal and jv_cmp overflows the C stack on deeply nested
input. Cap recursion at 10000 with -1 / INT_MIN sentinels;
operators that compose user expressions surface this as
"Equality check too deep" / "Comparison too deep".

Fixes CVE-2026-47770.

src/builtin.c

@@ -297,7 +297,15 @@ jv binop_minus(jv a, jv b) {
     jv_array_foreach(a, i, x) {
       int include = 1;
       jv_array_foreach(b, j, y) {
-        if (jv_equal(jv_copy(x), y)) {
+        int equal = jv_equal(jv_copy(x), y);
+        if (equal < 0) {
+          jv_free(out);
+          jv_free(x);
+          jv_free(a);
+          jv_free(b);
+          return jv_invalid_with_msg(jv_string("Equality check too deep"));
+        }
+        if (equal) {
           include = 0;
           break;
         }
@@ -381,11 +389,17 @@ jv binop_mod(jv a, jv b) {
 #undef dtoi
 
 jv binop_equal(jv a, jv b) {
-  return jv_bool(jv_equal(a, b));
+  int r = jv_equal(a, b);
+  if (r < 0)
+    return jv_invalid_with_msg(jv_string("Equality check too deep"));
+  return jv_bool(r);
 }
 
 jv binop_notequal(jv a, jv b) {
-  return jv_bool(!jv_equal(a, b));
+  int r = jv_equal(a, b);
+  if (r < 0)
+    return jv_invalid_with_msg(jv_string("Equality check too deep"));
+  return jv_bool(!r);
 }
 
 enum cmp_op {
@@ -397,6 +411,8 @@ enum cmp_op {
 
 static jv order_cmp(jv a, jv b, enum cmp_op op) {
   int r = jv_cmp(a, b);
+  if (r == INT_MIN)
+    return jv_invalid_with_msg(jv_string("Comparison too deep"));
   return jv_bool((op == CMP_OP_LESS && r < 0) ||
                  (op == CMP_OP_LESSEQ && r <= 0) ||
                  (op == CMP_OP_GREATEREQ && r >= 0) ||
@@ -868,6 +884,12 @@ static jv f_bsearch(jq_state *jq, jv input, jv target) {
   while (start < end) {
     int mid = start + (end - start) / 2;
     int result = jv_cmp(jv_copy(target), jv_array_get(jv_copy(input), mid));
+    if (result == INT_MIN) {
+      jv_free(answer);
+      jv_free(input);
+      jv_free(target);
+      return jv_invalid_with_msg(jv_string("Comparison too deep"));
+    }
     if (result == 0) {
       answer = jv_number(mid);
       break;
@@ -1159,6 +1181,14 @@ static jv minmax_by(jv values, jv keys, int is_min) {
   for (int i=1; i<jv_array_length(jv_copy(values)); i++) {
     jv item = jv_array_get(jv_copy(keys), i);
     int cmp = jv_cmp(jv_copy(item), jv_copy(retkey));
+    if (cmp == INT_MIN) {
+      jv_free(item);
+      jv_free(values);
+      jv_free(keys);
+      jv_free(retkey);
+      jv_free(ret);
+      return jv_invalid_with_msg(jv_string("Comparison too deep"));
+    }
     if ((cmp < 0) == (is_min == 1)) {
       jv_free(retkey);
       retkey = item;

src/jv.c

@@ -896,16 +896,20 @@ static jv* jvp_array_write(jv* a, int i) {
   }
 }
 
-static int jvp_array_equal(jv a, jv b) {
+static int jvp_equal(jv a, jv b, int depth);
+
+static int jvp_array_equal(jv a, jv b, int depth) {
   if (jvp_array_length(a) != jvp_array_length(b))
     return 0;
   if (jvp_array_ptr(a) == jvp_array_ptr(b) &&
       jvp_array_offset(a) == jvp_array_offset(b))
     return 1;
   for (int i=0; i<jvp_array_length(a); i++) {
-    if (!jv_equal(jv_copy(*jvp_array_read(a, i)),
-                  jv_copy(*jvp_array_read(b, i))))
-      return 0;
+    int r = jvp_equal(jv_copy(*jvp_array_read(a, i)),
+                      jv_copy(*jvp_array_read(b, i)),
+                      depth);
+    if (r <= 0)
+      return r;
   }
   return 1;
 }
@@ -1055,7 +1059,14 @@ jv jv_array_indexes(jv a, jv b) {
   int alen = jv_array_length(jv_copy(a));
   for (int ai = 0; ai < alen; ++ai) {
     jv_array_foreach(b, bi, belem) {
-      if (!jv_equal(jv_array_get(jv_copy(a), ai + bi), belem))
+      int equal = jv_equal(jv_array_get(jv_copy(a), ai + bi), belem);
+      if (equal < 0) {
+        jv_free(res);
+        jv_free(a);
+        jv_free(b);
+        return jv_invalid_with_msg(jv_string("Equality check too deep"));
+      }
+      if (!equal)
         idx = -1;
       else if (bi == 0 && idx == -1)
         idx = ai;
@@ -1799,7 +1810,7 @@ static int jvp_object_length(jv object) {
   return n;
 }
 
-static int jvp_object_equal(jv o1, jv o2) {
+static int jvp_object_equal(jv o1, jv o2, int depth) {
   int len2 = jvp_object_length(o2);
   int len1 = 0;
   for (int i=0; i<jvp_object_size(o1); i++) {
@@ -1808,7 +1819,8 @@ static int jvp_object_equal(jv o1, jv o2) {
     jv* slot2 = jvp_object_read(o2, slot->string);
     if (!slot2) return 0;
     // FIXME: do less refcounting here
-    if (!jv_equal(jv_copy(slot->value), jv_copy(*slot2))) return 0;
+    int r = jvp_equal(jv_copy(slot->value), jv_copy(*slot2), depth);
+    if (r <= 0) return r;
     len1++;
   }
   return len1 == len2;
@@ -2067,7 +2079,16 @@ int jv_get_refcnt(jv j) {
  * Higher-level operations
  */
 
-int jv_equal(jv a, jv b) {
+#ifndef MAX_EQUAL_DEPTH
+#define MAX_EQUAL_DEPTH (10000)
+#endif
+
+static int jvp_equal(jv a, jv b, int depth) {
+  if (depth > MAX_EQUAL_DEPTH) {
+    jv_free(a);
+    jv_free(b);
+    return -1;
+  }
   int r;
   if (jv_get_kind(a) != jv_get_kind(b)) {
     r = 0;
@@ -2083,13 +2104,13 @@ int jv_equal(jv a, jv b) {
       r = jvp_number_equal(a, b);
       break;
     case JV_KIND_ARRAY:
-      r = jvp_array_equal(a, b);
+      r = jvp_array_equal(a, b, depth + 1);
       break;
     case JV_KIND_STRING:
       r = jvp_string_equal(a, b);
       break;
     case JV_KIND_OBJECT:
-      r = jvp_object_equal(a, b);
+      r = jvp_object_equal(a, b, depth + 1);
       break;
     default:
       r = 1;
@@ -2101,6 +2122,11 @@ int jv_equal(jv a, jv b) {
   return r;
 }
 
+// Returns 1 if equal, 0 if not equal, or -1 if the comparison is too deep
+int jv_equal(jv a, jv b) {
+  return jvp_equal(a, b, 0);
+}
+
 int jv_identical(jv a, jv b) {
   int r;
   if (a.kind_flags != b.kind_flags

src/jv_aux.c

@@ -16,6 +16,24 @@ static double jv_number_get_value_and_consume(jv number) {
   return value;
 }
 
+#ifndef MAX_CMP_DEPTH
+#define MAX_CMP_DEPTH (10000)
+#endif
+
+struct sort_cmp_state {
+  int too_deep;
+};
+
+#ifdef _MSC_VER
+static __declspec(thread) struct sort_cmp_state sort_cmp_state;
+#else
+#ifdef HAVE___THREAD
+static __thread struct sort_cmp_state sort_cmp_state;
+#else
+static struct sort_cmp_state sort_cmp_state;
+#endif
+#endif
+
 static jv parse_slice(jv j, jv slice, int* pstart, int* pend) {
   // Array slices
   jv start_jv = jv_object_get(jv_copy(slice), jv_string("start"));
@@ -463,7 +481,7 @@ static jv delpaths_sorted(jv object, jv paths, int start) {
     do
       j++;
     while (j < jv_array_length(jv_copy(paths)) &&
-           jv_equal(jv_copy(key), jv_array_get(jv_array_get(jv_copy(paths), j), start)));
+           jv_equal(jv_copy(key), jv_array_get(jv_array_get(jv_copy(paths), j), start)) == 1);
     // if i <= entry < j, then entry starts with key
     if (delkey) {
       // deleting this entire key, we don't care about any more specific deletions
@@ -597,7 +615,13 @@ jv jv_keys(jv x) {
   }
 }
 
-int jv_cmp(jv a, jv b) {
+static int jvp_cmp(jv a, jv b, int depth) {
+  if (depth > MAX_CMP_DEPTH) {
+    jv_free(a);
+    jv_free(b);
+    return INT_MIN;
+  }
+
   if (jv_get_kind(a) != jv_get_kind(b)) {
     int r = (int)jv_get_kind(a) - (int)jv_get_kind(b);
     jv_free(a);
@@ -612,14 +636,13 @@ int jv_cmp(jv a, jv b) {
   case JV_KIND_FALSE:
   case JV_KIND_TRUE:
     // there's only one of each of these values
-    r = 0;
     break;
 
   case JV_KIND_NUMBER: {
     if (jvp_number_is_nan(a)) {
-      r = jv_cmp(jv_null(), jv_copy(b));
+      r = jvp_cmp(jv_null(), jv_copy(b), depth);
     } else if (jvp_number_is_nan(b)) {
-      r = jv_cmp(jv_copy(a), jv_null());
+      r = jvp_cmp(jv_copy(a), jv_null(), depth);
     } else {
       r = jvp_number_cmp(a, b);
     }
@@ -643,7 +666,9 @@ int jv_cmp(jv a, jv b) {
       }
       jv xa = jv_array_get(jv_copy(a), i);
       jv xb = jv_array_get(jv_copy(b), i);
-      r = jv_cmp(xa, xb);
+      r = jvp_cmp(xa, xb, depth + 1);
+      if (r == INT_MIN)
+        break;
       i++;
     }
     break;
@@ -652,13 +677,14 @@ int jv_cmp(jv a, jv b) {
   case JV_KIND_OBJECT: {
     jv keys_a = jv_keys(jv_copy(a));
     jv keys_b = jv_keys(jv_copy(b));
-    r = jv_cmp(jv_copy(keys_a), keys_b);
+    r = jvp_cmp(jv_copy(keys_a), keys_b, depth + 1);
     if (r == 0) {
       jv_array_foreach(keys_a, i, key) {
         jv xa = jv_object_get(jv_copy(a), jv_copy(key));
         jv xb = jv_object_get(jv_copy(b), key);
-        r = jv_cmp(xa, xb);
-        if (r) break;
+        r = jvp_cmp(xa, xb, depth + 1);
+        if (r != 0)
+          break;
       }
     }
     jv_free(keys_a);
@@ -671,6 +697,11 @@ int jv_cmp(jv a, jv b) {
   return r;
 }
 
+// Returns <0, 0, >0 if a is less than, equal to, or greater than b, or
+// INT_MIN if the comparison is too deep
+int jv_cmp(jv a, jv b) {
+  return jvp_cmp(a, b, 0);
+}
 
 struct sort_entry {
   jv object;
@@ -678,19 +709,32 @@ struct sort_entry {
   int index;
 };
 
+static void sort_entry_array_free(struct sort_entry* entries, int start, int n) {
+  for (int i = start; i < n; i++) {
+    jv_free(entries[i].key);
+    jv_free(entries[i].object);
+  }
+  jv_mem_free(entries);
+}
+
 static int sort_cmp(const void* pa, const void* pb) {
   const struct sort_entry* a = pa;
   const struct sort_entry* b = pb;
   int r = jv_cmp(jv_copy(a->key), jv_copy(b->key));
+  if (r == INT_MIN) {
+    sort_cmp_state.too_deep = 1;
+    return 0;
+  }
   // comparing by index if r == 0 makes the sort stable
   return r ? r : (a->index - b->index);
 }
 
-static struct sort_entry* sort_items(jv objects, jv keys) {
+static struct sort_entry* sort_items(jv objects, jv keys, int *too_deep) {
   assert(jv_get_kind(objects) == JV_KIND_ARRAY);
   assert(jv_get_kind(keys) == JV_KIND_ARRAY);
   assert(jv_array_length(jv_copy(objects)) == jv_array_length(jv_copy(keys)));
   int n = jv_array_length(jv_copy(objects));
+  *too_deep = 0;
   if (n == 0) {
     jv_free(objects);
     jv_free(keys);
@@ -704,7 +748,13 @@ static struct sort_entry* sort_items(jv objects, jv keys) {
   }
   jv_free(objects);
   jv_free(keys);
+  sort_cmp_state.too_deep = 0;
   qsort(entries, n, sizeof(struct sort_entry), sort_cmp);
+  if (sort_cmp_state.too_deep) {
+    sort_entry_array_free(entries, 0, n);
+    *too_deep = 1;
+    return NULL;
+  }
   return entries;
 }
 
@@ -713,7 +763,10 @@ jv jv_sort(jv objects, jv keys) {
   assert(jv_get_kind(keys) == JV_KIND_ARRAY);
   assert(jv_array_length(jv_copy(objects)) == jv_array_length(jv_copy(keys)));
   int n = jv_array_length(jv_copy(objects));
-  struct sort_entry* entries = sort_items(objects, keys);
+  int too_deep = 0;
+  struct sort_entry* entries = sort_items(objects, keys, &too_deep);
+  if (too_deep)
+    return jv_invalid_with_msg(jv_string("Comparison too deep"));
   jv ret = jv_array();
   for (int i=0; i<n; i++) {
     jv_free(entries[i].key);
@@ -728,13 +781,24 @@ jv jv_group(jv objects, jv keys) {
   assert(jv_get_kind(keys) == JV_KIND_ARRAY);
   assert(jv_array_length(jv_copy(objects)) == jv_array_length(jv_copy(keys)));
   int n = jv_array_length(jv_copy(objects));
-  struct sort_entry* entries = sort_items(objects, keys);
+  int too_deep = 0;
+  struct sort_entry* entries = sort_items(objects, keys, &too_deep);
+  if (too_deep)
+    return jv_invalid_with_msg(jv_string("Comparison too deep"));
   jv ret = jv_array();
   if (n > 0) {
     jv curr_key = entries[0].key;
     jv group = jv_array_append(jv_array(), entries[0].object);
     for (int i = 1; i < n; i++) {
-      if (jv_equal(jv_copy(curr_key), jv_copy(entries[i].key))) {
+      int equal = jv_equal(jv_copy(curr_key), jv_copy(entries[i].key));
+      if (equal < 0) {
+        jv_free(curr_key);
+        jv_free(group);
+        sort_entry_array_free(entries, i, n);
+        jv_free(ret);
+        return jv_invalid_with_msg(jv_string("Equality check too deep"));
+      }
+      if (equal) {
         jv_free(entries[i].key);
       } else {
         jv_free(curr_key);
@@ -756,11 +820,21 @@ jv jv_unique(jv objects, jv keys) {
   assert(jv_get_kind(keys) == JV_KIND_ARRAY);
   assert(jv_array_length(jv_copy(objects)) == jv_array_length(jv_copy(keys)));
   int n = jv_array_length(jv_copy(objects));
-  struct sort_entry* entries = sort_items(objects, keys);
+  int too_deep = 0;
+  struct sort_entry* entries = sort_items(objects, keys, &too_deep);
+  if (too_deep)
+    return jv_invalid_with_msg(jv_string("Comparison too deep"));
   jv ret = jv_array();
   jv curr_key = jv_invalid();
   for (int i = 0; i < n; i++) {
-    if (jv_equal(jv_copy(curr_key), jv_copy(entries[i].key))) {
+    int equal = jv_equal(jv_copy(curr_key), jv_copy(entries[i].key));
+    if (equal < 0) {
+      jv_free(curr_key);
+      sort_entry_array_free(entries, i, n);
+      jv_free(ret);
+      return jv_invalid_with_msg(jv_string("Equality check too deep"));
+    }
+    if (equal) {
       jv_free(entries[i].key);
       jv_free(entries[i].object);
     } else {

tests/jq.test

@@ -2611,3 +2611,25 @@ null
 try (reduce range(10001) as $_ ({}; {a: .}) as $x | $x * $x) catch .
 null
 "Object merge too deep"
+
+# regression test for deep structural equality recursion
+try ((reduce range(10001) as $_ ([]; [.])) as $x | (reduce range(10001) as $_ ([]; [.])) as $y | $x == $y) catch .
+null
+"Equality check too deep"
+
+# regression tests for deep ordering comparisons
+try ((reduce range(10001) as $_ ([]; [.])) as $x | [$x, $x] | sort) catch .
+null
+"Comparison too deep"
+
+try ((reduce range(10001) as $_ ([]; [.])) as $x | [$x, $x] | unique) catch .
+null
+"Comparison too deep"
+
+try ((reduce range(10001) as $_ ({}; {a: .})) as $x | [$x, $x] | sort) catch .
+null
+"Comparison too deep"
+
+try ((reduce range(10001) as $_ ({}; {a: .})) as $x | [$x, $x] | unique) catch .
+null
+"Comparison too deep"