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    Subject[34-longterm 045/209] sys_semctl: fix kernel stack leakage
    Date
    From: Dan Rosenberg <drosenberg@vsecurity.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@gmail.com>
    Cc: Manfred Spraul <manfred@colorfullife.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.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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