diff options
| author | Herbert Xu <herbert@gondor.apana.org.au> | 2015-07-13 16:04:13 +0800 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2015-12-06 00:49:05 +0100 |
| commit | 52501955df29e42b29d4e8dea6b3c4332adccdd6 (patch) | |
| tree | 8dfc0be1d0a9234d05ea38c21f2e2c6f6a729a6f | |
| parent | 4ad8ce65628e282aece91d6139fd556f7864f950 (diff) | |
net: Clone skb before setting peeked flag
commit 738ac1ebb96d02e0d23bc320302a6ea94c612dec upstream.
Shared skbs must not be modified and this is crucial for broadcast
and/or multicast paths where we use it as an optimisation to avoid
unnecessary cloning.
The function skb_recv_datagram breaks this rule by setting peeked
without cloning the skb first. This causes funky races which leads
to double-free.
This patch fixes this by cloning the skb and replacing the skb
in the list when setting skb->peeked.
Fixes: a59322be07c9 ("[UDP]: Only increment counter on first peek/recv")
Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 72e6f0680249f5e0a87f2b282d033baefd90d84e)
[wt: adjusted context for 2.6.32. Introduces a bug, see next commit]
Signed-off-by: Willy Tarreau <w@1wt.eu>
| -rw-r--r-- | net/core/datagram.c | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/net/core/datagram.c b/net/core/datagram.c index 4ade3011bb3c..cbb3100c37dc 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -127,6 +127,35 @@ out_noerr: goto out; } +static int skb_set_peeked(struct sk_buff *skb) +{ + struct sk_buff *nskb; + + if (skb->peeked) + return 0; + + /* We have to unshare an skb before modifying it. */ + if (!skb_shared(skb)) + goto done; + + nskb = skb_clone(skb, GFP_ATOMIC); + if (!nskb) + return -ENOMEM; + + skb->prev->next = nskb; + skb->next->prev = nskb; + nskb->prev = skb->prev; + nskb->next = skb->next; + + consume_skb(skb); + skb = nskb; + +done: + skb->peeked = 1; + + return 0; +} + /** * __skb_recv_datagram - Receive a datagram skbuff * @sk: socket @@ -160,6 +189,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, int *peeked, int *err) { struct sk_buff *skb; + unsigned long cpu_flags; long timeo; /* * Caller is allowed not to check sk->sk_err before skb_recv_datagram() @@ -178,14 +208,16 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, * Look at current nfs client by the way... * However, this function was corrent in any case. 8) */ - unsigned long cpu_flags; - spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags); skb = skb_peek(&sk->sk_receive_queue); if (skb) { *peeked = skb->peeked; if (flags & MSG_PEEK) { - skb->peeked = 1; + + error = skb_set_peeked(skb); + if (error) + goto unlock_err; + atomic_inc(&skb->users); } else __skb_unlink(skb, &sk->sk_receive_queue); @@ -204,6 +236,8 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags, return NULL; +unlock_err: + spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags); no_packet: *err = error; return NULL; |