[Openvpn-devel] [PATCH 4/5 v2] buffer_list_aggregate_separator(): prevent 0-byte malloc

[Steffan K. <ste...@fo...>]

As pointed out in finding OVPN-05 of the cryptograpy engineering audit
(funded by Private Internet Access), buffer_list_aggregate_separator()
could perform a 0-byte malloc when called with a list of 0-length buffers
and a "" separator.  If other could would later try to access that buffer
memory, this would result in undefined behaviour.  To prevent this, always
malloc() 1 byte.

To simplify as we go, use alloc_buf() to allocate the buffer.  This has
the additional benefit that the actual buffer data (not the contents) is
zero-terminated, because alloc_buf() calls calloc() and we have 1 extra
byte of data.

Signed-off-by: Steffan Karger <ste...@fo...>
---
v2: add spaces around '+'

 src/openvpn/buffer.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/openvpn/buffer.c b/src/openvpn/buffer.c
index 2656702..cfe6f2c 100644
--- a/src/openvpn/buffer.c
+++ b/src/openvpn/buffer.c
@@ -1251,8 +1251,7 @@ buffer_list_aggregate_separator(struct buffer_list *bl, const size_t max_len,
             struct buffer_entry *e = bl->head, *f;
 
             ALLOC_OBJ_CLEAR(f, struct buffer_entry);
-            f->buf.data = malloc(size);
-            check_malloc_return(f->buf.data);
+            f->buf = alloc_buf(size + 1); /* prevent 0-byte malloc */
             f->buf.capacity = size;
             for (i = 0; e && i < count; ++i)
             {
-- 
2.7.4