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net/packet: remove data races in fanout operations

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af_packet fanout uses RCU rules to ensure f->arr elements
are not dismantled before RCU grace period.

However, it lacks rcu accessors to make sure KCSAN and other tools
wont detect data races. Stupid compilers could also play games.

Fixes: dc99f60069 ("packet: Add fanout support.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: "Gong, Sishuai" <sishuai@purdue.edu>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-04-14 12:36:44 -07:00 committed by David S. Miller
parent ae1ea84b33
commit 94f633ea8a
2 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
net/packet/af_packet.c
View File

@ -1359,7 +1359,7 @@ static unsigned int fanout_demux_rollover(struct packet_fanout *f,
struct packet_sock *po, *po_next, *po_skip = NULL;
unsigned int i, j, room = ROOM_NONE;
po = pkt_sk(f->arr[idx]);
po = pkt_sk(rcu_dereference(f->arr[idx]));
if (try_self) {
room = packet_rcv_has_room(po, skb);
@ -1371,7 +1371,7 @@ static unsigned int fanout_demux_rollover(struct packet_fanout *f,
i = j = min_t(int, po->rollover->sock, num - 1);
do {
po_next = pkt_sk(f->arr[i]);
po_next = pkt_sk(rcu_dereference(f->arr[i]));
if (po_next != po_skip && !READ_ONCE(po_next->pressure) &&
packet_rcv_has_room(po_next, skb) == ROOM_NORMAL) {
if (i != j)
@ -1466,7 +1466,7 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev,
if (fanout_has_flag(f, PACKET_FANOUT_FLAG_ROLLOVER))
idx = fanout_demux_rollover(f, skb, idx, true, num);
po = pkt_sk(f->arr[idx]);
po = pkt_sk(rcu_dereference(f->arr[idx]));
return po->prot_hook.func(skb, dev, &po->prot_hook, orig_dev);
}
@ -1480,7 +1480,7 @@ static void __fanout_link(struct sock *sk, struct packet_sock *po)
struct packet_fanout *f = po->fanout;
spin_lock(&f->lock);
f->arr[f->num_members] = sk;
rcu_assign_pointer(f->arr[f->num_members], sk);
smp_wmb();
f->num_members++;
if (f->num_members == 1)
@ -1495,11 +1495,14 @@ static void __fanout_unlink(struct sock *sk, struct packet_sock *po)
spin_lock(&f->lock);
for (i = 0; i < f->num_members; i++) {
if (f->arr[i] == sk)
if (rcu_dereference_protected(f->arr[i],
lockdep_is_held(&f->lock)) == sk)
break;
}
BUG_ON(i >= f->num_members);
f->arr[i] = f->arr[f->num_members - 1];
rcu_assign_pointer(f->arr[i],
rcu_dereference_protected(f->arr[f->num_members - 1],
lockdep_is_held(&f->lock)));
f->num_members--;
if (f->num_members == 0)
__dev_remove_pack(&f->prot_hook);

2
net/packet/internal.h
View File

@ -94,7 +94,7 @@ struct packet_fanout {
spinlock_t lock;
refcount_t sk_ref;
struct packet_type prot_hook ____cacheline_aligned_in_smp;
struct sock *arr[];
struct sock __rcu *arr[];
};
struct packet_rollover {