[PATCH] udp: Fix udp_poll() and ioctl()

Eric Dumazet
2009-10-09T14:43:40Z

Eric Dumazet a écrit :
> Eric Dumazet a écrit :
>> Eric Dumazet a écrit :
>>> Eric Dumazet a écrit :
>>>> Rafael J. Wysocki a écrit :
>>>>> This message has been generated automatically as a part of a report
>>>>> of regressions introduced between 2.6.30 and 2.6.31.
>>>>>
>>>>> The following bug entry is on the current list of known regressions
>>>>> introduced between 2.6.30 and 2.6.31. Please verify if it still should
>>>>> be listed and let me know (either way).
>>>>>
>>>>>
>>>>> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=14301
>>>>> Subject : WARNING: at net/ipv4/af_inet.c:154
>>>>> Submitter : Ralf Hildebrandt <Ralf.Hildebrandt@charite.de>
>>>>> Date : 2009-09-30 12:24 (2 days old)
>>>>> References : http://marc.info/?l=linux-kernel&m=125431350218137&w=4
>>>>>
>> Investigation still needed...
>>
>
> OK, my last (buggy ???) feeling is about commit 95766fff6b9a78d1
>
> [UDP]: Add memory accounting.
>
> (Its a two years old patch, oh well...)
>
> Problem is the udp_poll() :
>
> We check the first frame to be dequeued from sk_receive_queue has a good checksum.
>
> If it doesnt, we drop the frame ( calling kfree_skb(skb); )
>
> Problem is now we perform memory accounting on UDP, this kfree_skb()
> should be done with socket locked, but are we allowed to
> call lock_sock() from this udp_poll() context ?
>

It seems we can lock_sock() from udp_poll() context, so here is a patch.

[PATCH] udp: Fix udp_poll()

udp_poll() can in some circumstances drop frames with incorrect checksums.

Problem is we now have to lock the socket while dropping frames, or risk
sk_forward corruption.

This bug is present since commit 95766fff6b9a78d1
([UDP]: Add memory accounting.)

While we are at it, we can correct ioctl(SIOCINQ) to also drop bad frames.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
net/ipv4/udp.c | 73 +++++++++++++++++++++++++++--------------------
1 files changed, 43 insertions(+), 30 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 6ec6a8a..d0d436d 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -841,6 +841,42 @@ out:
return ret;
}

+
+/**
+ * first_packet_length - return length of first packet in receive queue
+ * @sk: socket
+ *
+ * Drops all bad checksum frames, until a valid one is found.
+ * Returns the length of found skb, or 0 if none is found.
+ */
+static unsigned int first_packet_length(struct sock *sk)
+{
+ struct sk_buff_head list_kill, *rcvq = &sk->sk_receive_queue;
+ struct sk_buff *skb;
+ unsigned int res;
+
+ __skb_queue_head_init(&list_kill);
+
+ spin_lock_bh(&rcvq->lock);
+ while ((skb = skb_peek(rcvq)) != NULL &&
+ udp_lib_checksum_complete(skb)) {
+ UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS,
+ IS_UDPLITE(sk));
+ __skb_unlink(skb, rcvq);
+ __skb_queue_tail(&list_kill, skb);
+ }
+ res = skb ? skb->len : 0;
+ spin_unlock_bh(&rcvq->lock);
+
+ if (!skb_queue_empty(&list_kill)) {
+ lock_sock(sk);
+ __skb_queue_purge(&list_kill);
+ sk_mem_reclaim_partial(sk);
+ release_sock(sk);
+ }
+ return res;
+}
+
/*
* IOCTL requests applicable to the UDP protocol
*/
@@ -857,21 +893,16 @@ int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)

case SIOCINQ:
{
- struct sk_buff *skb;
- unsigned long amount;
+ unsigned int amount = first_packet_length(sk);

- amount = 0;
- spin_lock_bh(&sk->sk_receive_queue.lock);
- skb = skb_peek(&sk->sk_receive_queue);
- if (skb != NULL) {
+ if (amount)
/*
* We will only return the amount
* of this packet since that is all
* that will be read.
*/
- amount = skb->len - sizeof(struct udphdr);
- }
- spin_unlock_bh(&sk->sk_receive_queue.lock);
+ amount -= sizeof(struct udphdr);
+
return put_user(amount, (int __user *)arg);
}

@@ -1540,29 +1571,11 @@ unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait)
{
unsigned int mask = datagram_poll(file, sock, wait);
struct sock *sk = sock->sk;
- int is_lite = IS_UDPLITE(sk);

/* Check for false positives due to checksum errors */
- if ((mask & POLLRDNORM) &&
- !(file->f_flags & O_NONBLOCK) &&
- !(sk->sk_shutdown & RCV_SHUTDOWN)) {
- struct sk_buff_head *rcvq = &sk->sk_receive_queue;
- struct sk_buff *skb;
-
- spin_lock_bh(&rcvq->lock);
- while ((skb = skb_peek(rcvq)) != NULL &&
- udp_lib_checksum_complete(skb)) {
- UDP_INC_STATS_BH(sock_net(sk),
- UDP_MIB_INERRORS, is_lite);
- __skb_unlink(skb, rcvq);
- kfree_skb(skb);
- }
- spin_unlock_bh(&rcvq->lock);
-
- /* nothing to see, move along */
- if (skb == NULL)
- mask &= ~(POLLIN | POLLRDNORM);
- }
+ if ((mask & POLLRDNORM) && !(file->f_flags & O_NONBLOCK) &&
+ !(sk->sk_shutdown & RCV_SHUTDOWN) && !first_packet_length(sk))
+ mask &= ~(POLLIN | POLLRDNORM);

return mask;