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inet: fix possible panic in reqsk_queue_unlink()

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[ 3897.923145] BUG: unable to handle kernel NULL pointer dereference at
 0000000000000080
[ 3897.931025] IP: [<ffffffffa9f27686>] reqsk_timer_handler+0x1a6/0x243

There is a race when reqsk_timer_handler() and tcp_check_req() call
inet_csk_reqsk_queue_unlink() on the same req at the same time.

Before commit fa76ce7328 ("inet: get rid of central tcp/dccp listener
timer"), listener spinlock was held and race could not happen.

To solve this bug, we change reqsk_queue_unlink() to not assume req
must be found, and we return a status, to conditionally release a
refcount on the request sock.

This also means tcp_check_req() in non fastopen case might or not
consume req refcount, so tcp_v6_hnd_req() & tcp_v4_hnd_req() have
to properly handle this.

(Same remark for dccp_check_req() and its callers)

inet_csk_reqsk_queue_drop() is now too big to be inlined, as it is
called 4 times in tcp and 3 times in dccp.

Fixes: fa76ce7328 ("inet: get rid of central tcp/dccp listener timer")
Signed-off-by: Eric Dumazet <[email protected]>
Reported-by: Yuchung Cheng <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2015-04-23 18:03:44 -07:00 • committed by David S. Miller
commit b357a364c5
9 changed files with 48 additions and 46 deletions
Download patch file Download diff file Expand all files Collapse all files

3
net/dccp/ipv4.c
View file

@ -453,7 +453,8 @@ static struct sock *dccp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
iph->saddr, iph->daddr);
if (req) {
nsk = dccp_check_req(sk, skb, req);
reqsk_put(req);
if (!nsk)
reqsk_put(req);
return nsk;
}
nsk = inet_lookup_established(sock_net(sk), &dccp_hashinfo,

3
net/dccp/ipv6.c
View file

@ -301,7 +301,8 @@ static struct sock *dccp_v6_hnd_req(struct sock *sk,struct sk_buff *skb)
&iph->daddr, inet6_iif(skb));
if (req) {
nsk = dccp_check_req(sk, skb, req);
reqsk_put(req);
if (!nsk)
reqsk_put(req);
return nsk;
}
nsk = __inet6_lookup_established(sock_net(sk), &dccp_hashinfo,

3
net/dccp/minisocks.c
View file

@ -186,8 +186,7 @@ struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
if (child == NULL)
goto listen_overflow;
inet_csk_reqsk_queue_unlink(sk, req);
inet_csk_reqsk_queue_removed(sk, req);
inet_csk_reqsk_queue_drop(sk, req);
inet_csk_reqsk_queue_add(sk, req, child);
out:
return child;