[PATCH 3.18 056/104] xen: Prevent buffer overflow in privcmd ioctl

From: Greg Kroah-Hartman
Date: Wed Apr 24 2019 - 13:13:19 EST

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

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.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 1246ae0bb992 ("xen: add variable hypercall caller")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/x86/include/asm/xen/hypercall.h | 3 +++
1 file changed, 3 insertions(+)

--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -213,6 +213,9 @@ privcmd_call(unsigned call,
__HYPERCALL_5ARG(a1, a2, a3, a4, a5);

+ if (call >= PAGE_SIZE / sizeof(hypercall_page[0]))
+ return -EINVAL;
asm volatile("call *%[call]"
: [call] "a" (&hypercall_page[call])