Have all of our allocation functions and a few others check for underflow

It's all too easy in C to convert an unsigned value to a signed one,
which will (on all modern computers) give you a huge signed value.  If
you have a size_t value of size greater than SSIZE_T_MAX, that is way
likelier to be an underflow than it is to be an actual request for
more than 2gb of memory in one go.  (There's nothing in Tor that
should be trying to allocate >2gb chunks.)

1 files changed, 3 insertions, 0 deletions

diff --git a/src/common/memarea.c b/src/common/memarea.c
index 9d908bae5..edd7bbe9e 100644
--- a/src/common/memarea.c
+++ b/src/common/memarea.c
@@ -73,6 +73,7 @@ static memarea_chunk_t *freelist = NULL;
 static memarea_chunk_t *
 alloc_chunk(size_t sz, int freelist_ok)
 {
+  tor_assert(sz < SIZE_T_CEILING);
   if (freelist && freelist_ok) {
     memarea_chunk_t *res = freelist;
     freelist = res->next_chunk;
@@ -182,6 +183,7 @@ memarea_alloc(memarea_t *area, size_t sz)
   memarea_chunk_t *chunk = area->first;
   char *result;
   tor_assert(chunk);
+  tor_assert(sz < SIZE_T_CEILING);
   if (sz == 0)
     sz = 1;
   if (chunk->next_mem+sz > chunk->u.mem+chunk->mem_size) {
@@ -240,6 +242,7 @@ memarea_strndup(memarea_t *area, const char *s, size_t n)
   size_t ln;
   char *result;
   const char *cp, *end = s+n;
+  tor_assert(n < SIZE_T_CEILING);
   for (cp = s; cp < end && *cp; ++cp)
     ;
   /* cp now points to s+n, or to the 0 in the string. */