Patch "bpf, array: fix heap out-of-bounds access when updating elements" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

bpf, array: fix heap out-of-bounds access when updating elements

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bpf-array-fix-heap-out-of-bounds-access-when-updating-elements.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Borkmann <[email protected]>
Date: Mon, 30 Nov 2015 13:02:56 +0100
Subject: bpf, array: fix heap out-of-bounds access when updating elements

From: Daniel Borkmann <[email protected]>

[ Upstream commit fbca9d2d35c6ef1b323fae75cc9545005ba25097 ]

During own review but also reported by Dmitry's syzkaller [1] it has been noticed that we trigger a heap out-of-bounds access on eBPF array maps when updating elements. This happens with each map whose map->value_size (specified during map creation time) is not multiple of 8 bytes.

In array_map_alloc(), elem_size is round_up(attr->value_size, 8) and used to align array map slots for faster access. However, in function array_map_update_elem(), we update the element as ...

memcpy(array->value + array->elem_size * index, value, array->elem_size);

... where we access 'value' out-of-bounds, since it was allocated from map_update_elem() from syscall side as kmalloc(map->value_size, GFP_USER) and later on copied through copy_from_user(value, uvalue, map->value_size). Thus, up to 7 bytes, we can access out-of-bounds.

Same could happen from within an eBPF program, where in worst case we access beyond an eBPF program's designated stack.

Since 1be7f75d1668 ("bpf: enable non-root eBPF programs") didn't hit an official release yet, it only affects priviledged users.

In case of array_map_lookup_elem(), the verifier prevents eBPF programs from accessing beyond map->value_size through check_map_access(). Also from syscall side map_lookup_elem() only copies map->value_size back to user, so nothing could leak.

[1] http://github.com/google/syzkaller

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

@@ -104,7 +104,7 @@ static int array_map_update_elem(struct
 		/* all elements already exist */
 		return -EEXIST;
 
-	memcpy(array->value + array->elem_size * index, value, array->elem_size);
+	memcpy(array->value + array->elem_size * index, value, map->value_size);
 	return 0;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/packet-infer-protocol-from-ethernet-header-if-unset.patch queue-4.2/bpf-array-fix-heap-out-of-bounds-access-when-updating-elements.patch queue-4.2/ipv6-sctp-implement-sctp_v6_destroy_sock.patch queue-4.2/packet-only-allow-extra-vlan-len-on-ethernet-devices.patch queue-4.2/net-scm-fix-pax-detected-msg_controllen-overflow-in-scm_detach_fds.patch queue-4.2/packet-fix-tpacket_snd-max-frame-len.patch queue-4.2/packet-always-probe-for-transport-header.patch queue-4.2/packet-do-skb_probe_transport_header-when-we-actually-have-data.patch queue-4.2/tools-net-use-include-uapi-with-__exported_headers__.patch