[PATCH] ipc: initialize structure memory to zero for shmctl

[PATCH] ipc: initialize structure memory to zero for shmctl

[Kees Cook]

The old shm interface will leak a few bytes of stack contents. Explicitly
initialize the structure to zero-fill the untouched fields.

Signed-off-by: Kees Cook <kees.cook@canonical.com>
---
 ipc/shm.c |   17 +++++++++--------
 1 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/ipc/shm.c b/ipc/shm.c
index 52ed77e..d2ee426 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -471,16 +471,17 @@ static inline unsigned long copy_shmid_to_user(void __user *buf, struct shmid64_
 		return copy_to_user(buf, in, sizeof(*in));
 	case IPC_OLD:
 	    {
-		struct shmid_ds out;
+		struct shmid_ds out = {
+			.shm_segsz	= in->shm_segsz,
+			.shm_atime	= in->shm_atime,
+			.shm_dtime	= in->shm_dtime,
+			.shm_ctime	= in->shm_ctime,
+			.shm_cpid	= in->shm_cpid,
+			.shm_lpid	= in->shm_lpid,
+			.shm_nattch	= in->shm_nattch,
+		};
 
 		ipc64_perm_to_ipc_perm(&in->shm_perm, &out.shm_perm);
-		out.shm_segsz	= in->shm_segsz;
-		out.shm_atime	= in->shm_atime;
-		out.shm_dtime	= in->shm_dtime;
-		out.shm_ctime	= in->shm_ctime;
-		out.shm_cpid	= in->shm_cpid;
-		out.shm_lpid	= in->shm_lpid;
-		out.shm_nattch	= in->shm_nattch;
 
 		return copy_to_user(buf, &out, sizeof(out));
 	    }
-- 
1.7.1


-- 
Kees Cook
Ubuntu Security Team

Re: [PATCH] ipc: initialize structure memory to zero for shmctl

[Al Viro]

On Wed, Oct 06, 2010 at 05:10:31PM -0700, Kees Cook wrote:
> The old shm interface will leak a few bytes of stack contents. Explicitly
> initialize the structure to zero-fill the untouched fields.

Umm...  I wonder if we ever have gaps in there; note that gaps between
the fields are _not_ initialized in compound literals.  Yes, I realize
that it's a separate problem, but explicit memset() prior to initializations
of fields might be a better solution, covering both.

Re: [PATCH] ipc: initialize structure memory to zero for shmctl

[Kees Cook]

Hi Al,

On Thu, Oct 07, 2010 at 02:21:36AM +0100, Al Viro wrote:
> On Wed, Oct 06, 2010 at 05:10:31PM -0700, Kees Cook wrote:
> > The old shm interface will leak a few bytes of stack contents. Explicitly
> > initialize the structure to zero-fill the untouched fields.
> 
> Umm...  I wonder if we ever have gaps in there; note that gaps between
> the fields are _not_ initialized in compound literals.  Yes, I realize
> that it's a separate problem, but explicit memset() prior to initializations
> of fields might be a better solution, covering both.

Excellent point. I'll resend with a memset.

-- 
Kees Cook
Ubuntu Security Team