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l2tp: avoid deadlock in l2tp stats update
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l2tp's u64_stats writers were incorrectly synchronised, making it possible to
deadlock a 64bit machine running a 32bit kernel simply by sending the l2tp
code netlink commands while passing data through l2tp sessions.

Previous discussion on netdev determined that alternative solutions such as
spinlock writer synchronisation or per-cpu data would bring unjustified
overhead, given that most users interested in high volume traffic will likely
be running 64bit kernels on 64bit hardware.

As such, this patch replaces l2tp's use of u64_stats with atomic_long_t,
thereby avoiding the deadlock.

Ref:
http://marc.info/?l=linux-netdev&m=134029167910731&w=2
http://marc.info/?l=linux-netdev&m=134079868111131&w=2

Signed-off-by: Tom Parkin <[email protected]>
Signed-off-by: James Chapman <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@tomparkin @davem330
tomparkin authored and davem330 committed Mar 20, 2013
1 parent cf2f5c8 commit 7b7c071
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Showing 5 changed files with 93 additions and 147 deletions.
75 changes: 19 additions & 56 deletions net/l2tp/l2tp_core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -374,20 +374,16 @@ static void l2tp_recv_queue_skb(struct l2tp_session *session, struct sk_buff *sk
struct sk_buff *skbp;
struct sk_buff *tmp;
u32 ns = L2TP_SKB_CB(skb)->ns;
struct l2tp_stats *sstats;

spin_lock_bh(&session->reorder_q.lock);
sstats = &session->stats;
skb_queue_walk_safe(&session->reorder_q, skbp, tmp) {
if (L2TP_SKB_CB(skbp)->ns > ns) {
__skb_queue_before(&session->reorder_q, skbp, skb);
l2tp_dbg(session, L2TP_MSG_SEQ,
"%s: pkt %hu, inserted before %hu, reorder_q len=%d\n",
session->name, ns, L2TP_SKB_CB(skbp)->ns,
skb_queue_len(&session->reorder_q));
u64_stats_update_begin(&sstats->syncp);
sstats->rx_oos_packets++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_oos_packets);
goto out;
}
}
Expand All @@ -404,23 +400,16 @@ static void l2tp_recv_dequeue_skb(struct l2tp_session *session, struct sk_buff *
{
struct l2tp_tunnel *tunnel = session->tunnel;
int length = L2TP_SKB_CB(skb)->length;
struct l2tp_stats *tstats, *sstats;

/* We're about to requeue the skb, so return resources
* to its current owner (a socket receive buffer).
*/
skb_orphan(skb);

tstats = &tunnel->stats;
u64_stats_update_begin(&tstats->syncp);
sstats = &session->stats;
u64_stats_update_begin(&sstats->syncp);
tstats->rx_packets++;
tstats->rx_bytes += length;
sstats->rx_packets++;
sstats->rx_bytes += length;
u64_stats_update_end(&tstats->syncp);
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&tunnel->stats.rx_packets);
atomic_long_add(length, &tunnel->stats.rx_bytes);
atomic_long_inc(&session->stats.rx_packets);
atomic_long_add(length, &session->stats.rx_bytes);

if (L2TP_SKB_CB(skb)->has_seq) {
/* Bump our Nr */
Expand Down Expand Up @@ -451,21 +440,17 @@ static void l2tp_recv_dequeue(struct l2tp_session *session)
{
struct sk_buff *skb;
struct sk_buff *tmp;
struct l2tp_stats *sstats;

/* If the pkt at the head of the queue has the nr that we
* expect to send up next, dequeue it and any other
* in-sequence packets behind it.
*/
start:
spin_lock_bh(&session->reorder_q.lock);
sstats = &session->stats;
skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
if (time_after(jiffies, L2TP_SKB_CB(skb)->expires)) {
u64_stats_update_begin(&sstats->syncp);
sstats->rx_seq_discards++;
sstats->rx_errors++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_seq_discards);
atomic_long_inc(&session->stats.rx_errors);
l2tp_dbg(session, L2TP_MSG_SEQ,
"%s: oos pkt %u len %d discarded (too old), waiting for %u, reorder_q_len=%d\n",
session->name, L2TP_SKB_CB(skb)->ns,
Expand Down Expand Up @@ -624,7 +609,6 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
struct l2tp_tunnel *tunnel = session->tunnel;
int offset;
u32 ns, nr;
struct l2tp_stats *sstats = &session->stats;

/* The ref count is increased since we now hold a pointer to
* the session. Take care to decrement the refcnt when exiting
Expand All @@ -641,9 +625,7 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
"%s: cookie mismatch (%u/%u). Discarding.\n",
tunnel->name, tunnel->tunnel_id,
session->session_id);
u64_stats_update_begin(&sstats->syncp);
sstats->rx_cookie_discards++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_cookie_discards);
goto discard;
}
ptr += session->peer_cookie_len;
Expand Down Expand Up @@ -712,9 +694,7 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
l2tp_warn(session, L2TP_MSG_SEQ,
"%s: recv data has no seq numbers when required. Discarding.\n",
session->name);
u64_stats_update_begin(&sstats->syncp);
sstats->rx_seq_discards++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_seq_discards);
goto discard;
}

Expand All @@ -733,9 +713,7 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
l2tp_warn(session, L2TP_MSG_SEQ,
"%s: recv data has no seq numbers when required. Discarding.\n",
session->name);
u64_stats_update_begin(&sstats->syncp);
sstats->rx_seq_discards++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_seq_discards);
goto discard;
}
}
Expand Down Expand Up @@ -789,9 +767,7 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
* packets
*/
if (L2TP_SKB_CB(skb)->ns != session->nr) {
u64_stats_update_begin(&sstats->syncp);
sstats->rx_seq_discards++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_seq_discards);
l2tp_dbg(session, L2TP_MSG_SEQ,
"%s: oos pkt %u len %d discarded, waiting for %u, reorder_q_len=%d\n",
session->name, L2TP_SKB_CB(skb)->ns,
Expand All @@ -817,9 +793,7 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
return;

discard:
u64_stats_update_begin(&sstats->syncp);
sstats->rx_errors++;
u64_stats_update_end(&sstats->syncp);
atomic_long_inc(&session->stats.rx_errors);
kfree_skb(skb);

if (session->deref)
Expand Down Expand Up @@ -861,7 +835,6 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
u32 tunnel_id, session_id;
u16 version;
int length;
struct l2tp_stats *tstats;

if (tunnel->sock && l2tp_verify_udp_checksum(tunnel->sock, skb))
goto discard_bad_csum;
Expand Down Expand Up @@ -950,10 +923,7 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
discard_bad_csum:
LIMIT_NETDEBUG("%s: UDP: bad checksum\n", tunnel->name);
UDP_INC_STATS_USER(tunnel->l2tp_net, UDP_MIB_INERRORS, 0);
tstats = &tunnel->stats;
u64_stats_update_begin(&tstats->syncp);
tstats->rx_errors++;
u64_stats_update_end(&tstats->syncp);
atomic_long_inc(&tunnel->stats.rx_errors);
kfree_skb(skb);

return 0;
Expand Down Expand Up @@ -1080,7 +1050,6 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
struct l2tp_tunnel *tunnel = session->tunnel;
unsigned int len = skb->len;
int error;
struct l2tp_stats *tstats, *sstats;

/* Debug */
if (session->send_seq)
Expand Down Expand Up @@ -1109,21 +1078,15 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
error = ip_queue_xmit(skb, fl);

/* Update stats */
tstats = &tunnel->stats;
u64_stats_update_begin(&tstats->syncp);
sstats = &session->stats;
u64_stats_update_begin(&sstats->syncp);
if (error >= 0) {
tstats->tx_packets++;
tstats->tx_bytes += len;
sstats->tx_packets++;
sstats->tx_bytes += len;
atomic_long_inc(&tunnel->stats.tx_packets);
atomic_long_add(len, &tunnel->stats.tx_bytes);
atomic_long_inc(&session->stats.tx_packets);
atomic_long_add(len, &session->stats.tx_bytes);
} else {
tstats->tx_errors++;
sstats->tx_errors++;
atomic_long_inc(&tunnel->stats.tx_errors);
atomic_long_inc(&session->stats.tx_errors);
}
u64_stats_update_end(&tstats->syncp);
u64_stats_update_end(&sstats->syncp);

return 0;
}
Expand Down
19 changes: 9 additions & 10 deletions net/l2tp/l2tp_core.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -36,16 +36,15 @@ enum {
struct sk_buff;

struct l2tp_stats {
u64 tx_packets;
u64 tx_bytes;
u64 tx_errors;
u64 rx_packets;
u64 rx_bytes;
u64 rx_seq_discards;
u64 rx_oos_packets;
u64 rx_errors;
u64 rx_cookie_discards;
struct u64_stats_sync syncp;
atomic_long_t tx_packets;
atomic_long_t tx_bytes;
atomic_long_t tx_errors;
atomic_long_t rx_packets;
atomic_long_t rx_bytes;
atomic_long_t rx_seq_discards;
atomic_long_t rx_oos_packets;
atomic_long_t rx_errors;
atomic_long_t rx_cookie_discards;
};

struct l2tp_tunnel;
Expand Down
28 changes: 14 additions & 14 deletions net/l2tp/l2tp_debugfs.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -146,14 +146,14 @@ static void l2tp_dfs_seq_tunnel_show(struct seq_file *m, void *v)
tunnel->sock ? atomic_read(&tunnel->sock->sk_refcnt) : 0,
atomic_read(&tunnel->ref_count));

seq_printf(m, " %08x rx %llu/%llu/%llu rx %llu/%llu/%llu\n",
seq_printf(m, " %08x rx %ld/%ld/%ld rx %ld/%ld/%ld\n",
tunnel->debug,
(unsigned long long)tunnel->stats.tx_packets,
(unsigned long long)tunnel->stats.tx_bytes,
(unsigned long long)tunnel->stats.tx_errors,
(unsigned long long)tunnel->stats.rx_packets,
(unsigned long long)tunnel->stats.rx_bytes,
(unsigned long long)tunnel->stats.rx_errors);
atomic_long_read(&tunnel->stats.tx_packets),
atomic_long_read(&tunnel->stats.tx_bytes),
atomic_long_read(&tunnel->stats.tx_errors),
atomic_long_read(&tunnel->stats.rx_packets),
atomic_long_read(&tunnel->stats.rx_bytes),
atomic_long_read(&tunnel->stats.rx_errors));

if (tunnel->show != NULL)
tunnel->show(m, tunnel);
Expand Down Expand Up @@ -203,14 +203,14 @@ static void l2tp_dfs_seq_session_show(struct seq_file *m, void *v)
seq_printf(m, "\n");
}

seq_printf(m, " %hu/%hu tx %llu/%llu/%llu rx %llu/%llu/%llu\n",
seq_printf(m, " %hu/%hu tx %ld/%ld/%ld rx %ld/%ld/%ld\n",
session->nr, session->ns,
(unsigned long long)session->stats.tx_packets,
(unsigned long long)session->stats.tx_bytes,
(unsigned long long)session->stats.tx_errors,
(unsigned long long)session->stats.rx_packets,
(unsigned long long)session->stats.rx_bytes,
(unsigned long long)session->stats.rx_errors);
atomic_long_read(&session->stats.tx_packets),
atomic_long_read(&session->stats.tx_bytes),
atomic_long_read(&session->stats.tx_errors),
atomic_long_read(&session->stats.rx_packets),
atomic_long_read(&session->stats.rx_bytes),
atomic_long_read(&session->stats.rx_errors));

if (session->show != NULL)
session->show(m, session);
Expand Down
72 changes: 28 additions & 44 deletions net/l2tp/l2tp_netlink.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -246,8 +246,6 @@ static int l2tp_nl_tunnel_send(struct sk_buff *skb, u32 portid, u32 seq, int fla
#if IS_ENABLED(CONFIG_IPV6)
struct ipv6_pinfo *np = NULL;
#endif
struct l2tp_stats stats;
unsigned int start;

hdr = genlmsg_put(skb, portid, seq, &l2tp_nl_family, flags,
L2TP_CMD_TUNNEL_GET);
Expand All @@ -265,28 +263,22 @@ static int l2tp_nl_tunnel_send(struct sk_buff *skb, u32 portid, u32 seq, int fla
if (nest == NULL)
goto nla_put_failure;

do {
start = u64_stats_fetch_begin(&tunnel->stats.syncp);
stats.tx_packets = tunnel->stats.tx_packets;
stats.tx_bytes = tunnel->stats.tx_bytes;
stats.tx_errors = tunnel->stats.tx_errors;
stats.rx_packets = tunnel->stats.rx_packets;
stats.rx_bytes = tunnel->stats.rx_bytes;
stats.rx_errors = tunnel->stats.rx_errors;
stats.rx_seq_discards = tunnel->stats.rx_seq_discards;
stats.rx_oos_packets = tunnel->stats.rx_oos_packets;
} while (u64_stats_fetch_retry(&tunnel->stats.syncp, start));

if (nla_put_u64(skb, L2TP_ATTR_TX_PACKETS, stats.tx_packets) ||
nla_put_u64(skb, L2TP_ATTR_TX_BYTES, stats.tx_bytes) ||
nla_put_u64(skb, L2TP_ATTR_TX_ERRORS, stats.tx_errors) ||
nla_put_u64(skb, L2TP_ATTR_RX_PACKETS, stats.rx_packets) ||
nla_put_u64(skb, L2TP_ATTR_RX_BYTES, stats.rx_bytes) ||
if (nla_put_u64(skb, L2TP_ATTR_TX_PACKETS,
atomic_long_read(&tunnel->stats.tx_packets)) ||
nla_put_u64(skb, L2TP_ATTR_TX_BYTES,
atomic_long_read(&tunnel->stats.tx_bytes)) ||
nla_put_u64(skb, L2TP_ATTR_TX_ERRORS,
atomic_long_read(&tunnel->stats.tx_errors)) ||
nla_put_u64(skb, L2TP_ATTR_RX_PACKETS,
atomic_long_read(&tunnel->stats.rx_packets)) ||
nla_put_u64(skb, L2TP_ATTR_RX_BYTES,
atomic_long_read(&tunnel->stats.rx_bytes)) ||
nla_put_u64(skb, L2TP_ATTR_RX_SEQ_DISCARDS,
stats.rx_seq_discards) ||
atomic_long_read(&tunnel->stats.rx_seq_discards)) ||
nla_put_u64(skb, L2TP_ATTR_RX_OOS_PACKETS,
stats.rx_oos_packets) ||
nla_put_u64(skb, L2TP_ATTR_RX_ERRORS, stats.rx_errors))
atomic_long_read(&tunnel->stats.rx_oos_packets)) ||
nla_put_u64(skb, L2TP_ATTR_RX_ERRORS,
atomic_long_read(&tunnel->stats.rx_errors)))
goto nla_put_failure;
nla_nest_end(skb, nest);

Expand Down Expand Up @@ -612,8 +604,6 @@ static int l2tp_nl_session_send(struct sk_buff *skb, u32 portid, u32 seq, int fl
struct nlattr *nest;
struct l2tp_tunnel *tunnel = session->tunnel;
struct sock *sk = NULL;
struct l2tp_stats stats;
unsigned int start;

sk = tunnel->sock;

Expand Down Expand Up @@ -656,28 +646,22 @@ static int l2tp_nl_session_send(struct sk_buff *skb, u32 portid, u32 seq, int fl
if (nest == NULL)
goto nla_put_failure;

do {
start = u64_stats_fetch_begin(&session->stats.syncp);
stats.tx_packets = session->stats.tx_packets;
stats.tx_bytes = session->stats.tx_bytes;
stats.tx_errors = session->stats.tx_errors;
stats.rx_packets = session->stats.rx_packets;
stats.rx_bytes = session->stats.rx_bytes;
stats.rx_errors = session->stats.rx_errors;
stats.rx_seq_discards = session->stats.rx_seq_discards;
stats.rx_oos_packets = session->stats.rx_oos_packets;
} while (u64_stats_fetch_retry(&session->stats.syncp, start));

if (nla_put_u64(skb, L2TP_ATTR_TX_PACKETS, stats.tx_packets) ||
nla_put_u64(skb, L2TP_ATTR_TX_BYTES, stats.tx_bytes) ||
nla_put_u64(skb, L2TP_ATTR_TX_ERRORS, stats.tx_errors) ||
nla_put_u64(skb, L2TP_ATTR_RX_PACKETS, stats.rx_packets) ||
nla_put_u64(skb, L2TP_ATTR_RX_BYTES, stats.rx_bytes) ||
if (nla_put_u64(skb, L2TP_ATTR_TX_PACKETS,
atomic_long_read(&session->stats.tx_packets)) ||
nla_put_u64(skb, L2TP_ATTR_TX_BYTES,
atomic_long_read(&session->stats.tx_bytes)) ||
nla_put_u64(skb, L2TP_ATTR_TX_ERRORS,
atomic_long_read(&session->stats.tx_errors)) ||
nla_put_u64(skb, L2TP_ATTR_RX_PACKETS,
atomic_long_read(&session->stats.rx_packets)) ||
nla_put_u64(skb, L2TP_ATTR_RX_BYTES,
atomic_long_read(&session->stats.rx_bytes)) ||
nla_put_u64(skb, L2TP_ATTR_RX_SEQ_DISCARDS,
stats.rx_seq_discards) ||
atomic_long_read(&session->stats.rx_seq_discards)) ||
nla_put_u64(skb, L2TP_ATTR_RX_OOS_PACKETS,
stats.rx_oos_packets) ||
nla_put_u64(skb, L2TP_ATTR_RX_ERRORS, stats.rx_errors))
atomic_long_read(&session->stats.rx_oos_packets)) ||
nla_put_u64(skb, L2TP_ATTR_RX_ERRORS,
atomic_long_read(&session->stats.rx_errors)))
goto nla_put_failure;
nla_nest_end(skb, nest);

Expand Down
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