Don't search off the end of the index for bad Olson ids.

In the old code, the index was a file to itself, so it made sense to
read until you hit the end of the file. In the new code, the index is
followed by hundreds of KiB of data, so we need to just search the
index.

Bug: 8368791
Change-Id: Icf5f8b5516cf3a93679fa849c9f6cd1cb100e0f1

1 files changed, 7 insertions, 1 deletions

diff --git a/libc/tzcode/localtime.c b/libc/tzcode/localtime.c
index 689bbd3..8a54e81 100644
--- a/libc/tzcode/localtime.c
+++ b/libc/tzcode/localtime.c
@@ -2305,7 +2305,13 @@ static int __bionic_open_tzdata_path(const char* path, const char* olson_id, int
 
   static const size_t NAME_LENGTH = 40;
   unsigned char buf[NAME_LENGTH + 3 * sizeof(int32_t)];
-  while (TEMP_FAILURE_RETRY(read(fd, buf, sizeof(buf))) == (ssize_t) sizeof(buf)) {
+
+  size_t id_count = (ntohl(header.data_offset) - ntohl(header.index_offset)) / sizeof(buf);
+  for (size_t i = 0; i < id_count; ++i) {
+    if (TEMP_FAILURE_RETRY(read(fd, buf, sizeof(buf))) != (ssize_t) sizeof(buf)) {
+      break;
+    }
+
     char this_id[NAME_LENGTH + 1];
     memcpy(this_id, buf, NAME_LENGTH);
     this_id[NAME_LENGTH] = '\0';