Reject exactly INT32_MAX and cover the accept path

An adversarial review of the in-memory bound found an off-by-one: the guard used
`> INT32_MAX`, but at `size + bufl == INT32_MAX` the unknown-length reallocs
compute `(int) size + bufl + 1 == INT32_MAX + 1`, a signed-overflow UB (it fails
safe because the negative width becomes a huge size_t and realloc returns NULL,
but it still aborts under UBSan). Use `>= INT32_MAX`.

The self-test gains a boundary case (that exact size must be refused, the teeth
for the off-by-one) and an accept case (a normal small size must not be), so a
stray `>` or a refuse-everything guard both fail it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Xavier Roche <roche@httrack.com>

src/htslib.c

@@ -2004,6 +2004,15 @@ LLint http_xfread1(htsblk * r, int bufl) {
 
   if (bufl > 0) {
     if (!r->is_write) {         // stocker en mémoire
+      // In-memory content must fit a 32-bit index (allocs below add 1, reads
+      // use int offsets): reject a hostile Content-Length or endless stream.
+      const LLint inmem_want =
+          (r->totalsize >= 0) ? r->totalsize : (r->size + bufl);
+      if (inmem_want >= INT32_MAX) {
+        r->statuscode = STATUSCODE_INVALID;
+        strcpybuff(r->msg, "In-memory content too large");
+        return READ_ERROR;
+      }
       if (r->totalsize >= 0) {  // totalsize déterminé ET ALLOUE
         if (r->adr == NULL) {
           r->adr = (char *) malloct((size_t) r->totalsize + 1);

src/htsselftest.c

@@ -1310,6 +1310,59 @@ static int st_headerlong(httrackp *opt, int argc, char **argv) {
   return 0;
 }
 
+/* http_xfread1 must refuse an in-memory buffer whose size would exceed a 32-bit
+   index (hostile Content-Length or endless stream) rather than allocate it.
+   The guard returns before any socket read, so no real connection is needed. */
+static int st_xfread_limit(httrackp *opt, int argc, char **argv) {
+  htsblk r;
+
+  (void) opt;
+  (void) argc;
+  (void) argv;
+
+  // Content-Length just over 2 GiB.
+  memset(&r, 0, sizeof(r));
+  r.soc = INVALID_SOCKET;
+  r.totalsize = (LLint) INT32_MAX + 1;
+  printf("bylen: refused=%d adr=%s msg=%s\n",
+         http_xfread1(&r, 8192) == READ_ERROR, r.adr != NULL ? "alloc" : "null",
+         r.msg);
+  if (r.adr != NULL)
+    freet(r.adr);
+
+  // Unknown length, buffer already at the limit: the next read would exceed it.
+  memset(&r, 0, sizeof(r));
+  r.soc = INVALID_SOCKET;
+  r.totalsize = -1;
+  r.size = (LLint) INT32_MAX;
+  printf("bygrow: refused=%d adr=%s msg=%s\n",
+         http_xfread1(&r, 8192) == READ_ERROR, r.adr != NULL ? "alloc" : "null",
+         r.msg);
+  if (r.adr != NULL)
+    freet(r.adr);
+
+  // Exactly at the 2 GiB index (size + bufl == INT32_MAX): must also be
+  // refused, since the reallocs below add 1 (a `> INT32_MAX` check would let
+  // this through and overflow the int realloc size).
+  memset(&r, 0, sizeof(r));
+  r.soc = INVALID_SOCKET;
+  r.totalsize = -1;
+  r.size = (LLint) INT32_MAX - 8192;
+  http_xfread1(&r, 8192);
+  printf("boundary: msg=%s\n", r.msg);
+
+  // A legitimate small size must NOT be refused by the guard (the read then
+  // fails on the invalid socket, but the size-too-large msg must not be set).
+  memset(&r, 0, sizeof(r));
+  r.soc = INVALID_SOCKET;
+  r.totalsize = 1000;
+  http_xfread1(&r, 8192);
+  printf("accept: msg=%s\n", r.msg);
+  if (r.adr != NULL)
+    freet(r.adr);
+  return 0;
+}
+
 /* Parse a Content-Range header and print the sanitized triple. A hostile value
    (negative or INT64 extreme) must clamp to 0 without signed-overflow UB. */
 static int st_crange(httrackp *opt, int argc, char **argv) {
@@ -2521,6 +2574,8 @@ static const struct selftest_entry {
      st_headerlong},
     {"crange", "<raw-content-range-line> ...",
      "Content-Range parse integer safety", st_crange},
+    {"xfread-limit", "", "in-memory receive buffer size bound",
+     st_xfread_limit},
     {"savename", "<fil> <content-type> [key=value ...]",
      "local save-name for a URL", st_savename},
     {"sniff", "<content-type> <hex:..|text>", "MIME magic consistency",

tests/01_engine-xfread.test

@@ -0,0 +1,29 @@
+#!/bin/bash
+#
+
+set -euo pipefail
+
+# http_xfread1 must refuse an in-memory receive buffer that would exceed a
+# 32-bit index (hostile Content-Length, or an endless stream) rather than
+# allocate it, while still accepting a normal small size. -#test=xfread-limit
+# drives both refusal paths and the accept path.
+
+out="$(httrack -O /dev/null -#test=xfread-limit)"
+for case in bylen bygrow; do
+    echo "$out" | grep -q "${case}: refused=1 adr=null msg=In-memory content too large" || {
+        echo "FAIL ${case}: $out"
+        exit 1
+    }
+done
+
+# Exactly INT32_MAX must be refused too (the reallocs add 1).
+echo "$out" | grep -q 'boundary: msg=In-memory content too large' || {
+    echo "FAIL boundary: $out"
+    exit 1
+}
+
+# The guard must NOT fire for a legitimate small size.
+if echo "$out" | grep -q 'accept: msg=In-memory content too large'; then
+    echo "FAIL accept (guard fired on a legit size): $out"
+    exit 1
+fi

tests/Makefile.am

@@ -66,6 +66,7 @@ TESTS = \
 	01_engine-urlhack.test \
 	01_engine-unescape-bounds.test \
 	01_engine-useragent.test \
+	01_engine-xfread.test \
 	01_zlib-acceptencoding.test \
 	01_zlib-cache.test \
 	01_zlib-cache-corrupt.test \