[PATCH 5.13 099/151] net: igmp: fix data-race in igmp_ifc_timer_expire()

Greg Kroah-Hartman
2021-08-16T13:30:28Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 4a2b285e7e103d4d6c6ed3e5052a0ff74a5d7f15 ]

Fix the data-race reported by syzbot [1]
Issue here is that igmp_ifc_timer_expire() can update in_dev->mr_ifc_count
while another change just occured from another context.

in_dev->mr_ifc_count is only 8bit wide, so the race had little
consequences.

[1]
BUG: KCSAN: data-race in igmp_ifc_event / igmp_ifc_timer_expire

write to 0xffff8881051e3062 of 1 bytes by task 12547 on cpu 0:
igmp_ifc_event+0x1d5/0x290 net/ipv4/igmp.c:821
igmp_group_added+0x462/0x490 net/ipv4/igmp.c:1356
____ip_mc_inc_group+0x3ff/0x500 net/ipv4/igmp.c:1461
__ip_mc_join_group+0x24d/0x2c0 net/ipv4/igmp.c:2199
ip_mc_join_group_ssm+0x20/0x30 net/ipv4/igmp.c:2218
do_ip_setsockopt net/ipv4/ip_sockglue.c:1285 [inline]
ip_setsockopt+0x1827/0x2a80 net/ipv4/ip_sockglue.c:1423
tcp_setsockopt+0x8c/0xa0 net/ipv4/tcp.c:3657
sock_common_setsockopt+0x5d/0x70 net/core/sock.c:3362
__sys_setsockopt+0x18f/0x200 net/socket.c:2159
__do_sys_setsockopt net/socket.c:2170 [inline]
__se_sys_setsockopt net/socket.c:2167 [inline]
__x64_sys_setsockopt+0x62/0x70 net/socket.c:2167
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881051e3062 of 1 bytes by interrupt on cpu 1:
igmp_ifc_timer_expire+0x706/0xa30 net/ipv4/igmp.c:808
call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1419
expire_timers+0x135/0x250 kernel/time/timer.c:1464
__run_timers+0x358/0x420 kernel/time/timer.c:1732
run_timer_softirq+0x19/0x30 kernel/time/timer.c:1745
__do_softirq+0x12c/0x26e kernel/softirq.c:558
invoke_softirq kernel/softirq.c:432 [inline]
__irq_exit_rcu+0x9a/0xb0 kernel/softirq.c:636
sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1100
asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
console_unlock+0x8e8/0xb30 kernel/printk/printk.c:2646
vprintk_emit+0x125/0x3d0 kernel/printk/printk.c:2174
vprintk_default+0x22/0x30 kernel/printk/printk.c:2185
vprintk+0x15a/0x170 kernel/printk/printk_safe.c:392
printk+0x62/0x87 kernel/printk/printk.c:2216
selinux_netlink_send+0x399/0x400 security/selinux/hooks.c:6041
security_netlink_send+0x42/0x90 security/security.c:2070
netlink_sendmsg+0x59e/0x7c0 net/netlink/af_netlink.c:1919
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg net/socket.c:723 [inline]
____sys_sendmsg+0x360/0x4d0 net/socket.c:2392
___sys_sendmsg net/socket.c:2446 [inline]
__sys_sendmsg+0x1ed/0x270 net/socket.c:2475
__do_sys_sendmsg net/socket.c:2484 [inline]
__se_sys_sendmsg net/socket.c:2482 [inline]
__x64_sys_sendmsg+0x42/0x50 net/socket.c:2482
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x01 -> 0x02

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12539 Comm: syz-executor.1 Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/igmp.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 6b3c558a4f23..a51360087b19 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -803,10 +803,17 @@ static void igmp_gq_timer_expire(struct timer_list *t)
static void igmp_ifc_timer_expire(struct timer_list *t)
{
struct in_device *in_dev = from_timer(in_dev, t, mr_ifc_timer);
+ u8 mr_ifc_count;

igmpv3_send_cr(in_dev);
- if (in_dev->mr_ifc_count) {
- in_dev->mr_ifc_count--;
+restart:
+ mr_ifc_count = READ_ONCE(in_dev->mr_ifc_count);
+
+ if (mr_ifc_count) {
+ if (cmpxchg(&in_dev->mr_ifc_count,
+ mr_ifc_count,
+ mr_ifc_count - 1) != mr_ifc_count)
+ goto restart;
igmp_ifc_start_timer(in_dev,
unsolicited_report_interval(in_dev));
}
@@ -818,7 +825,7 @@ static void igmp_ifc_event(struct in_device *in_dev)
struct net *net = dev_net(in_dev->dev);
if (IGMP_V1_SEEN(in_dev) || IGMP_V2_SEEN(in_dev))
return;
- in_dev->mr_ifc_count = in_dev->mr_qrv ?: net->ipv4.sysctl_igmp_qrv;
+ WRITE_ONCE(in_dev->mr_ifc_count, in_dev->mr_qrv ?: net->ipv4.sysctl_igmp_qrv);
igmp_ifc_start_timer(in_dev, 1);
}

@@ -957,7 +964,7 @@ static bool igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
in_dev->mr_qri;
}
/* cancel the interface change timer */
- in_dev->mr_ifc_count = 0;
+ WRITE_ONCE(in_dev->mr_ifc_count, 0);
if (del_timer(&in_dev->mr_ifc_timer))
__in_dev_put(in_dev);
/* clear deleted report items */
@@ -1724,7 +1731,7 @@ void ip_mc_down(struct in_device *in_dev)
igmp_group_dropped(pmc);

#ifdef CONFIG_IP_MULTICAST
- in_dev->mr_ifc_count = 0;
+ WRITE_ONCE(in_dev->mr_ifc_count, 0);
if (del_timer(&in_dev->mr_ifc_timer))
__in_dev_put(in_dev);
in_dev->mr_gq_running = 0;
@@ -1941,7 +1948,7 @@ static int ip_mc_del_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
pmc->sfmode = MCAST_INCLUDE;
#ifdef CONFIG_IP_MULTICAST
pmc->crcount = in_dev->mr_qrv ?: net->ipv4.sysctl_igmp_qrv;
- in_dev->mr_ifc_count = pmc->crcount;
+ WRITE_ONCE(in_dev->mr_ifc_count, pmc->crcount);
for (psf = pmc->sources; psf; psf = psf->sf_next)
psf->sf_crcount = 0;
igmp_ifc_event(pmc->interface);
@@ -2120,7 +2127,7 @@ static int ip_mc_add_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
/* else no filters; keep old mode for reports */

pmc->crcount = in_dev->mr_qrv ?: net->ipv4.sysctl_igmp_qrv;
- in_dev->mr_ifc_count = pmc->crcount;
+ WRITE_ONCE(in_dev->mr_ifc_count, pmc->crcount);
for (psf = pmc->sources; psf; psf = psf->sf_next)
psf->sf_crcount = 0;
igmp_ifc_event(in_dev);
--
2.30.2