[4/5] buffer_list_aggregate_separator(): prevent 0-byte malloc

Message ID 1498913642-32459-4-git-send-email-steffan.karger@fox-it.com
State Superseded
Headers show
Series
  • [1/5] buffer_list_aggregate_separator(): add unit tests
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Commit Message

Steffan Karger July 1, 2017, 12:54 p.m.
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 <steffan.karger@fox-it.com>
---
 src/openvpn/buffer.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Patch

diff --git a/src/openvpn/buffer.c b/src/openvpn/buffer.c
index 2700ad1..ecbdc1b 100644
--- a/src/openvpn/buffer.c
+++ b/src/openvpn/buffer.c
@@ -1261,8 +1261,7 @@  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)
             {