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Subject[PATCH 5.1 28/62] net: bridge: mcast: fix stale nsrcs pointer in igmp3/mld2 report handling
Date
From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>

[ Upstream commit e57f61858b7cf478ed6fa23ed4b3876b1c9625c4 ]

We take a pointer to grec prior to calling pskb_may_pull and use it
afterwards to get nsrcs so record nsrcs before the pull when handling
igmp3 and we get a pointer to nsrcs and call pskb_may_pull when handling
mld2 which again could lead to reading 2 bytes out-of-bounds.

==================================================================
BUG: KASAN: use-after-free in br_multicast_rcv+0x480c/0x4ad0 [bridge]
Read of size 2 at addr ffff8880421302b4 by task ksoftirqd/1/16

CPU: 1 PID: 16 Comm: ksoftirqd/1 Tainted: G OE 5.2.0-rc6+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Call Trace:
dump_stack+0x71/0xab
print_address_description+0x6a/0x280
? br_multicast_rcv+0x480c/0x4ad0 [bridge]
__kasan_report+0x152/0x1aa
? br_multicast_rcv+0x480c/0x4ad0 [bridge]
? br_multicast_rcv+0x480c/0x4ad0 [bridge]
kasan_report+0xe/0x20
br_multicast_rcv+0x480c/0x4ad0 [bridge]
? br_multicast_disable_port+0x150/0x150 [bridge]
? ktime_get_with_offset+0xb4/0x150
? __kasan_kmalloc.constprop.6+0xa6/0xf0
? __netif_receive_skb+0x1b0/0x1b0
? br_fdb_update+0x10e/0x6e0 [bridge]
? br_handle_frame_finish+0x3c6/0x11d0 [bridge]
br_handle_frame_finish+0x3c6/0x11d0 [bridge]
? br_pass_frame_up+0x3a0/0x3a0 [bridge]
? virtnet_probe+0x1c80/0x1c80 [virtio_net]
br_handle_frame+0x731/0xd90 [bridge]
? select_idle_sibling+0x25/0x7d0
? br_handle_frame_finish+0x11d0/0x11d0 [bridge]
__netif_receive_skb_core+0xced/0x2d70
? virtqueue_get_buf_ctx+0x230/0x1130 [virtio_ring]
? do_xdp_generic+0x20/0x20
? virtqueue_napi_complete+0x39/0x70 [virtio_net]
? virtnet_poll+0x94d/0xc78 [virtio_net]
? receive_buf+0x5120/0x5120 [virtio_net]
? __netif_receive_skb_one_core+0x97/0x1d0
__netif_receive_skb_one_core+0x97/0x1d0
? __netif_receive_skb_core+0x2d70/0x2d70
? _raw_write_trylock+0x100/0x100
? __queue_work+0x41e/0xbe0
process_backlog+0x19c/0x650
? _raw_read_lock_irq+0x40/0x40
net_rx_action+0x71e/0xbc0
? __switch_to_asm+0x40/0x70
? napi_complete_done+0x360/0x360
? __switch_to_asm+0x34/0x70
? __switch_to_asm+0x40/0x70
? __schedule+0x85e/0x14d0
__do_softirq+0x1db/0x5f9
? takeover_tasklets+0x5f0/0x5f0
run_ksoftirqd+0x26/0x40
smpboot_thread_fn+0x443/0x680
? sort_range+0x20/0x20
? schedule+0x94/0x210
? __kthread_parkme+0x78/0xf0
? sort_range+0x20/0x20
kthread+0x2ae/0x3a0
? kthread_create_worker_on_cpu+0xc0/0xc0
ret_from_fork+0x35/0x40

The buggy address belongs to the page:
page:ffffea0001084c00 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0
flags: 0xffffc000000000()
raw: 00ffffc000000000 ffffea0000cfca08 ffffea0001098608 0000000000000000
raw: 0000000000000000 0000000000000003 00000000ffffff7f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888042130180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888042130200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff888042130280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888042130300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888042130380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
Disabling lock debugging due to kernel taint

Fixes: bc8c20acaea1 ("bridge: multicast: treat igmpv3 report with INCLUDE and no sources as a leave")
Reported-by: Martin Weinelt <martin@linuxlounge.net>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Tested-by: Martin Weinelt <martin@linuxlounge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/bridge/br_multicast.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -934,6 +934,7 @@ static int br_ip4_multicast_igmp3_report
int type;
int err = 0;
__be32 group;
+ u16 nsrcs;

ih = igmpv3_report_hdr(skb);
num = ntohs(ih->ngrec);
@@ -947,8 +948,9 @@ static int br_ip4_multicast_igmp3_report
grec = (void *)(skb->data + len - sizeof(*grec));
group = grec->grec_mca;
type = grec->grec_type;
+ nsrcs = ntohs(grec->grec_nsrcs);

- len += ntohs(grec->grec_nsrcs) * 4;
+ len += nsrcs * 4;
if (!ip_mc_may_pull(skb, len))
return -EINVAL;

@@ -969,7 +971,7 @@ static int br_ip4_multicast_igmp3_report
src = eth_hdr(skb)->h_source;
if ((type == IGMPV3_CHANGE_TO_INCLUDE ||
type == IGMPV3_MODE_IS_INCLUDE) &&
- ntohs(grec->grec_nsrcs) == 0) {
+ nsrcs == 0) {
br_ip4_multicast_leave_group(br, port, group, vid, src);
} else {
err = br_ip4_multicast_add_group(br, port, group, vid,
@@ -1006,7 +1008,8 @@ static int br_ip6_multicast_mld2_report(
len = skb_transport_offset(skb) + sizeof(*icmp6h);

for (i = 0; i < num; i++) {
- __be16 *nsrcs, _nsrcs;
+ __be16 *_nsrcs, __nsrcs;
+ u16 nsrcs;

nsrcs_offset = len + offsetof(struct mld2_grec, grec_nsrcs);

@@ -1014,12 +1017,13 @@ static int br_ip6_multicast_mld2_report(
nsrcs_offset + sizeof(_nsrcs))
return -EINVAL;

- nsrcs = skb_header_pointer(skb, nsrcs_offset,
- sizeof(_nsrcs), &_nsrcs);
- if (!nsrcs)
+ _nsrcs = skb_header_pointer(skb, nsrcs_offset,
+ sizeof(__nsrcs), &__nsrcs);
+ if (!_nsrcs)
return -EINVAL;

- grec_len = struct_size(grec, grec_src, ntohs(*nsrcs));
+ nsrcs = ntohs(*_nsrcs);
+ grec_len = struct_size(grec, grec_src, nsrcs);

if (!ipv6_mc_may_pull(skb, len + grec_len))
return -EINVAL;
@@ -1044,7 +1048,7 @@ static int br_ip6_multicast_mld2_report(
src = eth_hdr(skb)->h_source;
if ((grec->grec_type == MLD2_CHANGE_TO_INCLUDE ||
grec->grec_type == MLD2_MODE_IS_INCLUDE) &&
- ntohs(*nsrcs) == 0) {
+ nsrcs == 0) {
br_ip6_multicast_leave_group(br, port, &grec->grec_mca,
vid, src);
} else {

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