[tor-commits] [tor/maint-0.4.0] Protect buffers against INT_MAX datalen overflows.

[teor at torproject.org]

commit 74b2bc43fbe61e3a04fe3f5cc9f817be307e13e1
Author: Tobias Stoeckmann <tobias at stoeckmann.org>
Date:   Tue Apr 9 11:59:20 2019 -0400

    Protect buffers against INT_MAX datalen overflows.
    
    Many buffer functions have a hard limit of INT_MAX for datalen, but
    this limitation is not enforced in all functions:
    
    - buf_move_all may exceed that limit with too many chunks
    - buf_move_to_buf exceeds that limit with invalid buf_flushlen argument
    - buf_new_with_data may exceed that limit (unit tests only)
    
    This patch adds some annotations in some buf_pos_t functions to
    guarantee that no out of boundary access could occur even if another
    function lacks safe guards against datalen overflows.
    
      [This is a backport of the submitted patch to 0.2.9, where the
      buf_move_to_buf and buf_new_with_data functions did not exist.]
---
 src/or/buffers.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/or/buffers.c b/src/or/buffers.c
index 89382d1d8..394ba0ccb 100644
--- a/src/or/buffers.c
+++ b/src/or/buffers.c
@@ -394,6 +394,10 @@ buf_free(buf_t *buf)
 {
   if (!buf)
     return;
+  if (BUG(buf_out->datalen >= INT_MAX || buf_in->datalen >= INT_MAX))
+    return;
+  if (BUG(buf_out->datalen >= INT_MAX - buf_in->datalen))
+    return;
 
   buf_clear(buf);
   buf->magic = 0xdeadbeef;
@@ -1034,6 +1038,7 @@ buf_find_pos_of_char(char ch, buf_pos_t *out)
 static inline int
 buf_pos_inc(buf_pos_t *pos)
 {
+  tor_assert(pos->pos < INT_MAX - 1);
   ++pos->pos;
   if (pos->pos == (off_t)pos->chunk->datalen) {
     if (!pos->chunk->next)
@@ -1925,6 +1930,7 @@ buf_find_offset_of_char(buf_t *buf, char ch)
 {
   chunk_t *chunk;
   off_t offset = 0;
+  tor_assert(buf->datalen < INT_MAX);
   for (chunk = buf->head; chunk; chunk = chunk->next) {
     char *cp = memchr(chunk->data, ch, chunk->datalen);
     if (cp)
@@ -2044,6 +2050,7 @@ assert_buf_ok(buf_t *buf)
     for (ch = buf->head; ch; ch = ch->next) {
       total += ch->datalen;
       tor_assert(ch->datalen <= ch->memlen);
+      tor_assert(ch->datalen < INT_MAX);
       tor_assert(ch->data >= &ch->mem[0]);
       tor_assert(ch->data <= &ch->mem[0]+ch->memlen);
       if (ch->data == &ch->mem[0]+ch->memlen) {