igmp: acquire pmc lock for ip_mc_clear_src()

[ Upstream commit c38b7d327aafd1e3ad7ff53eefac990673b65667 ]

Andrey reported a use-after-free in add_grec():

        for (psf = *psf_list; psf; psf = psf_next) {
		...
                psf_next = psf->sf_next;

where the struct ip_sf_list's were already freed by:

 kfree+0xe8/0x2b0 mm/slub.c:3882
 ip_mc_clear_src+0x69/0x1c0 net/ipv4/igmp.c:2078
 ip_mc_dec_group+0x19a/0x470 net/ipv4/igmp.c:1618
 ip_mc_drop_socket+0x145/0x230 net/ipv4/igmp.c:2609
 inet_release+0x4e/0x1c0 net/ipv4/af_inet.c:411
 sock_release+0x8d/0x1e0 net/socket.c:597
 sock_close+0x16/0x20 net/socket.c:1072

This happens because we don't hold pmc->lock in ip_mc_clear_src()
and a parallel mr_ifc_timer timer could jump in and access them.

The RCU lock is there but it is merely for pmc itself, this
spinlock could actually ensure we don't access them in parallel.

Thanks to Eric and Long for discussion on this bug.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 17adfdaf57957e42eec77abcbede42b83faf47db..e719019867902361eb6f06e3f9fe99f83d155c9f 100644 (file)
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -2026,21 +2026,26 @@ static int ip_mc_add_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
 
 static void ip_mc_clear_src(struct ip_mc_list *pmc)
 {
-       struct ip_sf_list *psf, *nextpsf;
+       struct ip_sf_list *psf, *nextpsf, *tomb, *sources;
 
-       for (psf = pmc->tomb; psf; psf = nextpsf) {
+       spin_lock_bh(&pmc->lock);
+       tomb = pmc->tomb;
+       pmc->tomb = NULL;
+       sources = pmc->sources;
+       pmc->sources = NULL;
+       pmc->sfmode = MCAST_EXCLUDE;
+       pmc->sfcount[MCAST_INCLUDE] = 0;
+       pmc->sfcount[MCAST_EXCLUDE] = 1;
+       spin_unlock_bh(&pmc->lock);
+
+       for (psf = tomb; psf; psf = nextpsf) {
                nextpsf = psf->sf_next;
                kfree(psf);
        }
-       pmc->tomb = NULL;
-       for (psf = pmc->sources; psf; psf = nextpsf) {
+       for (psf = sources; psf; psf = nextpsf) {
                nextpsf = psf->sf_next;
                kfree(psf);
        }
-       pmc->sources = NULL;
-       pmc->sfmode = MCAST_EXCLUDE;
-       pmc->sfcount[MCAST_INCLUDE] = 0;
-       pmc->sfcount[MCAST_EXCLUDE] = 1;
 }
 
 /* Join a multicast group