xen: Prevent buffer overflow in privcmd ioctl

commit 42d8644bd77dd2d747e004e367cb0c895a606f39 upstream.

The "call" variable comes from the user in privcmd_ioctl_hypercall().
It's an offset into the hypercall_page[] which has (PAGE_SIZE / 32)
elements.  We need to put an upper bound on it to prevent an out of
bounds access.

Fixes: 1246ae0bb992 ("xen: add variable hypercall caller")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index da45f9fc1913922f76c4acfa682c97e33622b393..5876b28f93315c74f88178024252ec002d9bb782 100644 (file)
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -215,6 +215,9 @@ privcmd_call(unsigned call,
        __HYPERCALL_DECLS;
        __HYPERCALL_5ARG(a1, a2, a3, a4, a5);
 
+       if (call >= PAGE_SIZE / sizeof(hypercall_page[0]))
+               return -EINVAL;
+
        stac();
        asm volatile(CALL_NOSPEC
                     : __HYPERCALL_5PARAM