From cefa91b2332d7009bc0be5d951d6cbbf349f90f8 Mon Sep 17 00:00:00 2001

From: Paolo Valerio <pvalerio@redhat.com>

Date: Fri, 15 Apr 2022 10:08:41 +0200

Subject: [PATCH] openvswitch: fix OOB access in reserve_sfa_size()

Git-commit: cefa91b2332d7009bc0be5d951d6cbbf349f90f8

Patch-mainline: v5.18-rc4

References: CVE-2022-2639 bsc#1202154

Given a sufficiently large number of actions, while copying and

reserving memory for a new action of a new flow, if next_offset is

greater than MAX_ACTIONS_BUFSIZE, the function reserve_sfa_size() does

not return -EMSGSIZE as expected, but it allocates MAX_ACTIONS_BUFSIZE

bytes increasing actions_len by req_size. This can then lead to an OOB

write access, especially when further actions need to be copied.

Fix it by rearranging the flow action size check.

KASAN splat below:

==================================================================

Bug: KASAN: slab-out-of-bounds in reserve_sfa_size+0x1ba/0x380 [openvswitch]

Write of size 65360 at addr ffff888147e4001c by task handler15/836

Cpu: 1 PID: 836 Comm: handler15 Not tainted 5.18.0-rc1+ #27

...

Call Trace:

 <TASK>

 dump_stack_lvl+0x45/0x5a

 print_report.cold+0x5e/0x5db

 ? __lock_text_start+0x8/0x8

 ? reserve_sfa_size+0x1ba/0x380 [openvswitch]

 kasan_report+0xb5/0x130

 ? reserve_sfa_size+0x1ba/0x380 [openvswitch]

 kasan_check_range+0xf5/0x1d0

 memcpy+0x39/0x60

 reserve_sfa_size+0x1ba/0x380 [openvswitch]

 __add_action+0x24/0x120 [openvswitch]

 ovs_nla_add_action+0xe/0x20 [openvswitch]

 ovs_ct_copy_action+0x29d/0x1130 [openvswitch]

 ? __kernel_text_address+0xe/0x30

 ? unwind_get_return_address+0x56/0xa0

 ? create_prof_cpu_mask+0x20/0x20

 ? ovs_ct_verify+0xf0/0xf0 [openvswitch]

 ? prep_compound_page+0x198/0x2a0

 ? __kasan_check_byte+0x10/0x40

 ? kasan_unpoison+0x40/0x70

 ? ksize+0x44/0x60

 ? reserve_sfa_size+0x75/0x380 [openvswitch]

 __ovs_nla_copy_actions+0xc26/0x2070 [openvswitch]

 ? __zone_watermark_ok+0x420/0x420

 ? validate_set.constprop.0+0xc90/0xc90 [openvswitch]

 ? __alloc_pages+0x1a9/0x3e0

 ? __alloc_pages_slowpath.constprop.0+0x1da0/0x1da0

 ? unwind_next_frame+0x991/0x1e40

 ? __mod_node_page_state+0x99/0x120

 ? __mod_lruvec_page_state+0x2e3/0x470

 ? __kasan_kmalloc_large+0x90/0xe0

 ovs_nla_copy_actions+0x1b4/0x2c0 [openvswitch]

 ovs_flow_cmd_new+0x3cd/0xb10 [openvswitch]

 ...

Cc: stable@vger.kernel.org

Fixes: f28cd2af22a0 ("openvswitch: fix flow actions reallocation")

Signed-off-by: Paolo Valerio <pvalerio@redhat.com>

Acked-by: Eelco Chaudron <echaudro@redhat.com>

Signed-off-by: David S. Miller <davem@davemloft.net>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 net/openvswitch/flow_netlink.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c

index 7176156d3844..4c09cf8a0ab2 100644

--- a/net/openvswitch/flow_netlink.c

+++ b/net/openvswitch/flow_netlink.c

@@ -2465,7 +2465,7 @@ static struct nlattr *reserve_sfa_size(struct sw_flow_actions **sfa,

 	new_acts_size = max(next_offset + req_size, ksize(*sfa) * 2);

 	if (new_acts_size > MAX_ACTIONS_BUFSIZE) {

-		if ((MAX_ACTIONS_BUFSIZE - next_offset) < req_size) {

+		if ((next_offset + req_size) > MAX_ACTIONS_BUFSIZE) {

 			OVS_NLERR(log, "Flow action size exceeds max %u",

 				  MAX_ACTIONS_BUFSIZE);

 			return ERR_PTR(-EMSGSIZE);

-- 

2.35.3