[032/127] sys_semctl: fix kernel stack leakage

[Greg KH]

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>

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@xxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 ipc/sem.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -560,6 +560,8 @@ static unsigned long copy_semid_to_user(
 	    {
 		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;


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