[PATCH] prctl: fix PR_SET_MM_AUXV kernel stack leak

[Alexey Dobriyan]

        prctl(PR_SET_MM, PR_SET_MM_AUXV, addr, 1);

will copy 1 byte from userspace to (quite big) on-stack array
and then stash everything to mm->saved_auxv.
AT_NULL terminator will be inserted at the very end.

/proc/*/auxv handler will find that AT_NULL terminator
and copy original stack contents to userspace.

This devious scheme requires CAP_SYS_RESOURCE.

Signed-off-by: Alexey Dobriyan <adobri...@gmail.com>
---

        apply to >=3.5

 kernel/sys.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2079,7 +2079,7 @@ static int prctl_set_auxv(struct mm_struct *mm, unsigned 
long addr,
         * up to the caller to provide sane values here, otherwise userspace
         * tools which use this vector might be unhappy.
         */
-       unsigned long user_auxv[AT_VECTOR_SIZE];
+       unsigned long user_auxv[AT_VECTOR_SIZE] = {};
 
        if (len > sizeof(user_auxv))
                return -EINVAL;