linux-kernel - [34-longterm 045/209] sys_semctl: fix kernel stack leakage

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Message-Id: <1302803039-9400-46-git-send-email-paul.gortmaker@windriver.com>
Date:	Thu, 14 Apr 2011 13:41:15 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org, Dan Rosenberg <drosenberg@...curity.com>,
	Dan Rosenberg <dan.j.rosenberg@...il.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 045/209] sys_semctl: fix kernel stack leakage

From: Dan Rosenberg <drosenberg@...curity.com>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit 982f7c2b2e6a28f8f266e075d92e19c0dd4c6e56 upstream.

The semctl syscall has several code paths that lead to the leakage of
uninitialized kernel stack memory (namely the IPC_INFO, SEM_INFO,
IPC_STAT, and SEM_STAT commands) during the use of the older, obsolete
version of the semid_ds struct.

The copy_semid_to_user() function declares a semid_ds struct on the stack
and copies it back to the user without initializing or zeroing the
"sem_base", "sem_pending", "sem_pending_last", and "undo" pointers,
allowing the leakage of 16 bytes of kernel stack memory.

The code is still reachable on 32-bit systems - when calling semctl()
newer glibc's automatically OR the IPC command with the IPC_64 flag, but
invoking the syscall directly allows users to use the older versions of
the struct.

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@...il.com>
Cc: Manfred Spraul <manfred@...orfullife.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 ipc/sem.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index dbef95b..b4c1641 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -608,6 +608,8 @@ static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in,
 	    {
 		struct semid_ds out;

+		memset(&out, 0, sizeof(out));
+
 		ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);

 		out.sem_otime	= in->sem_otime;
-- 
1.7.4.4

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