When a timer is deleted and not re-armed in igmp_mod_timer(), the code currently decrements the reference counter of the multicast list entry @im using refcount_dec(&im->refcnt). However, igmp_mod_timer() can be called from the RCU reader path (e.g., in igmp_heard_query() via for_each_pmc_rcu()). If the group im was concurrently removed from the list by ip_mc_dec_group(), its reference count might have already been decremented to 1. In this case, timer_delete() succeeds, and refcount_dec() decrements the refcount from 1 to 0. Since refcount_dec() does not free the object when it hits 0 (unlike ip_ma_put()), the im structure is leaked. Fix this by using ip_ma_put(im) instead of refcount_dec(&im->refcnt). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet --- net/ipv4/igmp.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c index f5f9763895641bf86bfcf9fd7fd7b06012fa4ece..2170b33ba147ce4990e3ee71ba4868e8696b00cb 100644 --- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -266,6 +266,8 @@ static void igmp_ifc_start_timer(struct in_device *in_dev, int delay) static void igmp_mod_timer(struct ip_mc_list *im, int max_delay) { + bool put = false; + spin_lock_bh(&im->lock); im->unsolicit_count = 0; if (timer_delete(&im->timer)) { @@ -275,10 +277,13 @@ static void igmp_mod_timer(struct ip_mc_list *im, int max_delay) spin_unlock_bh(&im->lock); return; } - refcount_dec(&im->refcnt); + put = true; } igmp_start_timer(im, max_delay); spin_unlock_bh(&im->lock); + + if (put) + ip_ma_put(im); } -- 2.55.0.rc0.799.gd6f94ed593-goog