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ipv4: igmp: annotate data-races around timer-related fields

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/proc/net/igmp walks the multicast list locklessly under RCU and reads
timer-related fields (im->tm_running, im->reporter, im->timer.expires)
to print the timer state of multicast memberships. Concurrently, these
fields are modified under im->lock spinlock in timer management paths
(igmp_stop_timer(), igmp_start_timer(), and igmp_timer_expire()). Fix this
intentional lockless snapshot by annotating the lockless reads with
READ_ONCE() and the updates with WRITE_ONCE().

Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260605014318.3890804-3-yuyanghuang@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Yuyang Huang 2026-06-05 10:43:18 +09:00 committed by Paolo Abeni
parent 1719841cab
commit 3289d17b7a
1 changed files with 13 additions and 11 deletions
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24
net/ipv4/igmp.c
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@ -220,8 +220,8 @@ static void igmp_stop_timer(struct ip_mc_list *im)
spin_lock_bh(&im->lock);
if (timer_delete(&im->timer))
refcount_dec(&im->refcnt);
im->tm_running = 0;
im->reporter = 0;
WRITE_ONCE(im->tm_running, 0);
WRITE_ONCE(im->reporter, 0);
im->unsolicit_count = 0;
spin_unlock_bh(&im->lock);
}
@ -231,7 +231,7 @@ static void igmp_start_timer(struct ip_mc_list *im, int max_delay)
{
int tv = get_random_u32_below(max_delay);
im->tm_running = 1;
WRITE_ONCE(im->tm_running, 1);
if (refcount_inc_not_zero(&im->refcnt)) {
if (mod_timer(&im->timer, jiffies + tv + 2))
ip_ma_put(im);
@ -267,7 +267,7 @@ static void igmp_mod_timer(struct ip_mc_list *im, int max_delay)
if (timer_delete(&im->timer)) {
if ((long)(im->timer.expires-jiffies) < max_delay) {
add_timer(&im->timer);
im->tm_running = 1;
WRITE_ONCE(im->tm_running, 1);
spin_unlock_bh(&im->lock);
return;
}
@ -857,12 +857,12 @@ static void igmp_timer_expire(struct timer_list *t)
struct in_device *in_dev = im->interface;
spin_lock(&im->lock);
im->tm_running = 0;
WRITE_ONCE(im->tm_running, 0);
if (im->unsolicit_count && --im->unsolicit_count)
igmp_start_timer(im, unsolicited_report_interval(in_dev));
im->reporter = 1;
WRITE_ONCE(im->reporter, 1);
spin_unlock(&im->lock);
if (IGMP_V1_SEEN(in_dev))
@ -1325,7 +1325,7 @@ static void __igmp_group_dropped(struct ip_mc_list *im, gfp_t gfp)
!READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
return;
reporter = im->reporter;
reporter = READ_ONCE(im->reporter);
igmp_stop_timer(im);
if (!in_dev->dead) {
@ -2963,6 +2963,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
struct ip_mc_list *im = v;
struct igmp_mc_iter_state *state = igmp_mc_seq_private(seq);
char *querier;
int tm_running;
long delta;
#ifdef CONFIG_IP_MULTICAST
@ -2980,13 +2981,14 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
querier);
}
delta = im->timer.expires - jiffies;
tm_running = READ_ONCE(im->tm_running);
delta = READ_ONCE(im->timer.expires) - jiffies;
seq_printf(seq,
"\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
im->multiaddr, READ_ONCE(im->users),
im->tm_running,
im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
im->reporter);
tm_running,
tm_running ? jiffies_delta_to_clock_t(delta) : 0,
READ_ONCE(im->reporter));
}
return 0;
}