[PATCH] wireless: fix 64K kernel heap content leak via ioctl

Kees Cook
2010-08-27T21:04:27Z

This problem was originally tracked down by Brad Spengler.

When calling wireless ioctls, if a driver does not correctly
validate/shrink iwp->length, the resulting copy_to_user can leak up to
64K of kernel heap contents.

It seems that this is triggerable[1] in 2.6.32 at least on ath5k, but
I was not able to track down how. The twisty maze of ioctl handlers
stumped me. :) Other drivers I checked did not appear to have any problems,
but the potential remains. I'm not sure if this patch is the right approach;
it was fixed differently[2] in grsecurity.

[1] http://forums.grsecurity.net/viewtopic.php?f=3&t=2290&start=0
[2] http://grsecurity.net/~spender/wireless-infoleak-fix2.patch

Reported-by: Brad Spengler <spender@grsecurity.net>
Signed-off-by: Kees Cook <kees.cook@canonical.com>
---
include/net/iw_handler.h | 1 -
net/wireless/wext-core.c | 26 ++------------------------
2 files changed, 2 insertions(+), 25 deletions(-)

diff --git a/include/net/iw_handler.h b/include/net/iw_handler.h
index 3afdb21..6c81f29 100644
--- a/include/net/iw_handler.h
+++ b/include/net/iw_handler.h
@@ -277,7 +277,6 @@
#define IW_DESCR_FLAG_EVENT 0x0002 /* Generate an event on SET */
#define IW_DESCR_FLAG_RESTRICT 0x0004 /* GET : request is ROOT only */
/* SET : Omit payload from generated iwevent */
-#define IW_DESCR_FLAG_NOMAX 0x0008 /* GET : no limit on request size */
/* Driver level flags */
#define IW_DESCR_FLAG_WAIT 0x0100 /* Wait for driver event */

diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 0ef17bc..55b1fd9 100644
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -82,7 +82,6 @@ static const struct iw_ioctl_description standard_ioctl[] = {
.header_type = IW_HEADER_TYPE_POINT,
.token_size = sizeof(struct iw_priv_args),
.max_tokens = 16,
- .flags = IW_DESCR_FLAG_NOMAX,
},
[IW_IOCTL_IDX(SIOCSIWSTATS)] = {
.header_type = IW_HEADER_TYPE_NULL,
@@ -134,7 +133,6 @@ static const struct iw_ioctl_description standard_ioctl[] = {
.token_size = sizeof(struct sockaddr) +
sizeof(struct iw_quality),
.max_tokens = IW_MAX_AP,
- .flags = IW_DESCR_FLAG_NOMAX,
},
[IW_IOCTL_IDX(SIOCSIWSCAN)] = {
.header_type = IW_HEADER_TYPE_POINT,
@@ -146,7 +144,6 @@ static const struct iw_ioctl_description standard_ioctl[] = {
.header_type = IW_HEADER_TYPE_POINT,
.token_size = 1,
.max_tokens = IW_SCAN_MAX_DATA,
- .flags = IW_DESCR_FLAG_NOMAX,
},
[IW_IOCTL_IDX(SIOCSIWESSID)] = {
.header_type = IW_HEADER_TYPE_POINT,
@@ -737,28 +734,9 @@ static int ioctl_standard_iw_point(struct iw_point *iwp, unsigned int cmd,
return -EFAULT;
/* Save user space buffer size for checking */
user_length = iwp->length;
-
- /* Don't check if user_length > max to allow forward
- * compatibility. The test user_length < min is
- * implied by the test at the end.
- */
-
- /* Support for very large requests */
- if ((descr->flags & IW_DESCR_FLAG_NOMAX) &&
- (user_length > descr->max_tokens)) {
- /* Allow userspace to GET more than max so
- * we can support any size GET requests.
- * There is still a limit : -ENOMEM.
- */
- extra_size = user_length * descr->token_size;
-
- /* Note : user_length is originally a __u16,
- * and token_size is controlled by us,
- * so extra_size won't get negative and
- * won't overflow...
- */
- }
}
+ /* Support for very large requests */
+ extra_size = max(extra_size, iwp->length * descr->token_size);

/* kzalloc() ensures NULL-termination for essid_compat. */
extra = kzalloc(extra_size, GFP_KERNEL);
--
1.7.1

--
Kees Cook
Ubuntu Security Team