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hardening: add safe FD_SET() wrapper openvpn_fd_set()

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On many platforms (not Windows, for once), FD_SET() can write outside the
given fd_set if an fd >= FD_SETSIZE is given.  To make sure we don't do
that, add an ASSERT() to error out with a clear error message when this
does happen.

This patch was inspired by remarks about FD_SET() from Sebastian Krahmer
of the SuSE Security Team.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1456996968-29472-1-git-send-email-steffan.karger@fox-it.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/11285
Signed-off-by: Gert Doering <gert@greenie.muc.de>
This commit is contained in:
Steffan Karger 2016-03-03 10:22:48 +01:00 committed by Gert Doering
parent 13de0103ea
commit e0b3fd49e2
5 changed files with 26 additions and 10 deletions
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8
src/openvpn/event.c
View file

@ -873,18 +873,18 @@ se_ctl (struct event_set *es, event_t event, unsigned int rwflags, void *arg)
if (ses->fast)
{
if (rwflags & EVENT_READ)
FD_SET (event, &ses->readfds);
openvpn_fd_set (event, &ses->readfds);
if (rwflags & EVENT_WRITE)
FD_SET (event, &ses->writefds);
openvpn_fd_set (event, &ses->writefds);
}
else
{
if (rwflags & EVENT_READ)
FD_SET (event, &ses->readfds);
openvpn_fd_set (event, &ses->readfds);
else
FD_CLR (event, &ses->readfds);
if (rwflags & EVENT_WRITE)
FD_SET (event, &ses->writefds);
openvpn_fd_set (event, &ses->writefds);
else
FD_CLR (event, &ses->writefds);
}

16
src/openvpn/fdmisc.h
View file

@ -22,10 +22,26 @@
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef FD_MISC_H
#define FD_MISC_H
#include "basic.h"
#include "error.h"
#include "syshead.h"
bool set_nonblock_action (int fd);
bool set_cloexec_action (int fd);
void set_nonblock (int fd);
void set_cloexec (int fd);
static inline void openvpn_fd_set(int fd, fd_set *setp)
{
#ifndef WIN32 /* The Windows FD_SET() implementation does not overflow */
ASSERT (fd >= 0 && fd < FD_SETSIZE);
#endif
FD_SET (fd, setp);
}
#undef FD_SET /* prevent direct use of FD_SET() */
#endif /* FD_MISC_H */

2
src/openvpn/proxy.c
View file

@ -92,7 +92,7 @@ recv_line (socket_descriptor_t sd,
}
FD_ZERO (&reads);
FD_SET (sd, &reads);
openvpn_fd_set (sd, &reads);
tv.tv_sec = timeout_sec;
tv.tv_usec = 0;

4
src/openvpn/socket.c
View file

@ -1003,7 +1003,7 @@ socket_listen_accept (socket_descriptor_t sd,
struct timeval tv;
FD_ZERO (&reads);
FD_SET (sd, &reads);
openvpn_fd_set (sd, &reads);
tv.tv_sec = 0;
tv.tv_usec = 0;
@ -1153,7 +1153,7 @@ openvpn_connect (socket_descriptor_t sd,
struct timeval tv;
FD_ZERO (&writes);
FD_SET (sd, &writes);
openvpn_fd_set (sd, &writes);
tv.tv_sec = 0;
tv.tv_usec = 0;

6
src/openvpn/socks.c
View file

@ -134,7 +134,7 @@ socks_username_password_auth (struct socks_proxy_info *p,
char c;
FD_ZERO (&reads);
FD_SET (sd, &reads);
openvpn_fd_set (sd, &reads);
tv.tv_sec = timeout_sec;
tv.tv_usec = 0;
@ -213,7 +213,7 @@ socks_handshake (struct socks_proxy_info *p,
char c;
FD_ZERO (&reads);
FD_SET (sd, &reads);
openvpn_fd_set (sd, &reads);
tv.tv_sec = timeout_sec;
tv.tv_usec = 0;
@ -319,7 +319,7 @@ recv_socks_reply (socket_descriptor_t sd,
char c;
FD_ZERO (&reads);
FD_SET (sd, &reads);
openvpn_fd_set (sd, &reads);
tv.tv_sec = timeout_sec;
tv.tv_usec = 0;