Signed-shift UB in zip-repair local-header read

unzRepair parses the local file header of a damaged cache zip during
repair. READ_32 combined two int-typed READ_16 halves as
READ_16(adr) | (READ_16((adr)+2) << 16); when the high half has bit 15
set (>= 0x8000), shifting it left by 16 exceeds INT_MAX, which is signed
overflow. UBSan aborts on the CRC/size fields of a header whose high
16-bit word has that bit set. Repair runs on hostile input (a corrupt or
foreign new.zip). Cast the halves to uLong before the shift, matching the
sibling minizip readers in unzip.c and zip.c.

Closes #639

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

src/htsselftest.c

@@ -2146,6 +2146,52 @@ static int st_cache_corrupt(httrackp *opt, int argc, char **argv) {
   return err;
 }
 
+/* Drives unzRepair over a damaged local file header whose CRC field's high
+   16-bit word has bit 15 set. Before the READ_32 fix that shifted an int and
+   overflowed, so UBSan aborts here; after it, repair recovers the one entry. */
+static int st_zip_repair_shift(httrackp *opt, int argc, char **argv) {
+  static const unsigned char zip[] = {
+      0x50, 0x4b, 0x03, 0x04, /* local file header signature */
+      0x14, 0x00,             /* version needed */
+      0x00, 0x00,             /* general purpose flag */
+      0x00, 0x00,             /* method */
+      0x00, 0x00,             /* time */
+      0x00, 0x00,             /* date */
+      0x00, 0x00, 0xe8, 0x8a, /* crc: high word 0x8ae8, bit 15 set */
+      0x00, 0x00, 0x00, 0x00, /* compressed size */
+      0x00, 0x00, 0x00, 0x00, /* uncompressed size */
+      0x01, 0x00,             /* filename length */
+      0x00, 0x00,             /* extra field length */
+      0x61                    /* filename "a" */
+  };
+  char in[HTS_URLMAXSIZE], out[HTS_URLMAXSIZE], tmp[HTS_URLMAXSIZE];
+  uLong nrec = 0, bytes = 0;
+  FILE *fp;
+  int err;
+
+  (void) opt;
+  if (argc < 1) {
+    fprintf(stderr, "zip-repair-shift: needs a directory\n");
+    return 1;
+  }
+  snprintf(in, sizeof(in), "%s/damaged.zip", argv[0]);
+  snprintf(out, sizeof(out), "%s/repair.zip", argv[0]);
+  snprintf(tmp, sizeof(tmp), "%s/repair.tmp", argv[0]);
+  fp = fopen(in, "wb");
+  if (fp == NULL || fwrite(zip, 1, sizeof(zip), fp) != sizeof(zip)) {
+    if (fp != NULL)
+      fclose(fp);
+    fprintf(stderr, "zip-repair-shift: cannot write %s\n", in);
+    return 1;
+  }
+  fclose(fp);
+  err = unzRepair(in, out, tmp, &nrec, &bytes);
+  printf("zip-repair-shift: %s (recovered %lu entr%s)\n",
+         (err == Z_OK && nrec == 1) ? "OK" : "FAIL", (unsigned long) nrec,
+         nrec == 1 ? "y" : "ies");
+  return (err == Z_OK && nrec == 1) ? 0 : 1;
+}
+
 static int st_cache_legacy(httrackp *opt, int argc, char **argv) {
   int err;
 
@@ -3253,6 +3299,9 @@ static const struct selftest_entry {
      st_cache_legacy},
     {"cache-corrupt", "<dir>", "cache read-side corruption self-test",
      st_cache_corrupt},
+    {"zip-repair-shift", "<dir>",
+     "cache zip-repair header read must not overflow a signed shift",
+     st_zip_repair_shift},
     {"dns", "", "DNS resolver/cache self-test", st_dns},
     {"dnstimeout", "", "a slow DNS resolve is bounded and holds no lock",
      st_dnstimeout},

src/minizip/mztools.c

@@ -14,7 +14,7 @@
 
 #define READ_8(adr)  ((unsigned char)*(adr))
 #define READ_16(adr) ( READ_8(adr) | (READ_8(adr+1) << 8) )
-#define READ_32(adr) ( READ_16(adr) | (READ_16((adr)+2) << 16) )
+#define READ_32(adr) ((uLong) READ_16(adr) | ((uLong) READ_16((adr) + 2) << 16))
 
 #define WRITE_8(buff, n) do { \
   *((unsigned char*)(buff)) = (unsigned char) ((n) & 0xff); \

tests/01_zlib-repair-shift.test

@@ -0,0 +1,21 @@
+#!/bin/bash
+#
+# Keep this POSIX-portable: the harness runs it via $(BASH), which is a plain
+# POSIX /bin/sh on some platforms (e.g. macOS), so avoid bashisms and GNU-only
+# tool flags despite the #!/bin/bash above.
+
+# unzRepair header read must not overflow a signed shift (-#test=zip-repair-shift
+# <dir>). A damaged local file header whose CRC high word has bit 15 set made
+# READ_32 shift an int past INT_MAX; UBSan aborts before the fix casts to uLong.
+
+set -eu
+
+dir=$(mktemp -d)
+trap 'rm -rf "$dir"' EXIT
+
+out=$(httrack -#test=zip-repair-shift "$dir")
+
+printf '%s\n' "$out" | grep -qx "zip-repair-shift: OK (recovered 1 entry)" || {
+    echo "expected 'zip-repair-shift: OK (recovered 1 entry)', got: $out" >&2
+    exit 1
+}

tests/Makefile.am

@@ -84,6 +84,7 @@ TESTS = \
 	01_zlib-cache-legacy.test \
 	01_zlib-cache-golden.test \
 	01_zlib-cache-writefail.test \
+	01_zlib-repair-shift.test \
 	01_zlib-savename-cached.test \
 	02_manpage-regen.test \
 	02_update-cache.test \