[PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()

[PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.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@google.com>
Reported-by: syzbot <syzkaller@googlegroups.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,
+			    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

Re: [PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue, 10 Aug 2021 02:45:47 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.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.
> 
> [...]

Here is the summary with links:
  - [net] net: igmp: fix data-race in igmp_ifc_timer_expire()
    https://git.kernel.org/netdev/net/c/4a2b285e7e10

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()

[Guenter Roeck]

On Tue, Aug 10, 2021 at 02:45:47AM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.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@google.com>
> Reported-by: syzbot <syzkaller@googlegroups.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
> 

Re: [PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()

[Guenter Roeck]

On Wed, Aug 11, 2021 at 11:29:25AM -0700, Guenter Roeck wrote:
> On Tue, Aug 10, 2021 at 02:45:47AM -0700, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.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@google.com>
> > Reported-by: syzbot <syzkaller@googlegroups.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
> 

Also:

Building arm:allmodconfig ... failed
--------------
Error log:
arm-linux-gnueabi-ld: net/ipv4/igmp.o: in function `igmp_ifc_timer_expire':
igmp.c:(.text+0x9b44): undefined reference to `__bad_cmpxchg'
make[1]: *** [Makefile:1176: vmlinux] Error 1
make: *** [Makefile:220: __sub-make] Error 2

Building xtensa:allmodconfig ... failed
--------------
Error log:
xtensa-linux-ld: net/ipv4/igmp.o: in function `igmp_gq_timer_expire':
igmp.c:(.text+0x4d4c): undefined reference to `__cmpxchg_called_with_bad_pointer'
xtensa-linux-ld: net/ipv4/igmp.o: in function `igmp_ifc_timer_expire':
igmp.c:(.text+0x4dad): undefined reference to `__cmpxchg_called_with_bad_pointer'

Guenter

Re: [PATCH net] net: igmp: fix data-race in igmp_ifc_timer_expire()

[Eric Dumazet]

Time to make mr_ifc_count a 32bit field then :/

On Wed, Aug 11, 2021 at 8:32 PM Guenter Roeck <linux@roeck-us.net> wrote:
>
> On Wed, Aug 11, 2021 at 11:29:25AM -0700, Guenter Roeck wrote:
> > On Tue, Aug 10, 2021 at 02:45:47AM -0700, Eric Dumazet wrote:
> > > From: Eric Dumazet <edumazet@google.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@google.com>
> > > Reported-by: syzbot <syzkaller@googlegroups.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
> >
>
> Also:
>
> Building arm:allmodconfig ... failed
> --------------
> Error log:
> arm-linux-gnueabi-ld: net/ipv4/igmp.o: in function `igmp_ifc_timer_expire':
> igmp.c:(.text+0x9b44): undefined reference to `__bad_cmpxchg'
> make[1]: *** [Makefile:1176: vmlinux] Error 1
> make: *** [Makefile:220: __sub-make] Error 2
>
> Building xtensa:allmodconfig ... failed
> --------------
> Error log:
> xtensa-linux-ld: net/ipv4/igmp.o: in function `igmp_gq_timer_expire':
> igmp.c:(.text+0x4d4c): undefined reference to `__cmpxchg_called_with_bad_pointer'
> xtensa-linux-ld: net/ipv4/igmp.o: in function `igmp_ifc_timer_expire':
> igmp.c:(.text+0x4dad): undefined reference to `__cmpxchg_called_with_bad_pointer'
>
> Guenter