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Date: Wed, 11 Aug 2021 11:29:23 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()
On Tue, Aug 10, 2021 at 02:45:47AM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> 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@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> ---
> 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 6b3c558a4f232652b97a078d48f302864e60a866..a51360087b19845a28408c827032e08dabf99838 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,
Unfortunately riscv only supports 4-byte and 8-byte cmpxchg(),
so this results in build errors.
Building riscv:defconfig ... failed
--------------
Error log:
In file included from <command-line>:
net/ipv4/igmp.c: In function 'igmp_ifc_timer_expire':
include/linux/compiler_types.h:328:45: error: call to '__compiletime_assert_547' declared with attribute error: BUILD_BUG failed
Guenter
> + 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);
> --
> 2.32.0.605.g8dce9f2422-goog
>
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