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author | Matthew Dawson <matthew@mjdsystems.ca> | 2017-08-18 15:04:54 -0400 |
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committer | David S. Miller <davem@davemloft.net> | 2017-08-18 15:12:54 -0700 |
commit | a0917e0bc6efc05834c0c1eafebd579a9c75e6e9 (patch) | |
tree | 31f8b60d8e7a0a20943057d7345fdca3558e5ed8 /net/core/datagram.c | |
parent | 2110ba58303f0c2a03360c5f81fbe67ed312e7b9 (diff) | |
download | op-kernel-dev-a0917e0bc6efc05834c0c1eafebd579a9c75e6e9.zip op-kernel-dev-a0917e0bc6efc05834c0c1eafebd579a9c75e6e9.tar.gz |
datagram: When peeking datagrams with offset < 0 don't skip empty skbs
Due to commit e6afc8ace6dd5cef5e812f26c72579da8806f5ac ("udp: remove
headers from UDP packets before queueing"), when udp packets are being
peeked the requested extra offset is always 0 as there is no need to skip
the udp header. However, when the offset is 0 and the next skb is
of length 0, it is only returned once. The behaviour can be seen with
the following python script:
from socket import *;
f=socket(AF_INET6, SOCK_DGRAM | SOCK_NONBLOCK, 0);
g=socket(AF_INET6, SOCK_DGRAM | SOCK_NONBLOCK, 0);
f.bind(('::', 0));
addr=('::1', f.getsockname()[1]);
g.sendto(b'', addr)
g.sendto(b'b', addr)
print(f.recvfrom(10, MSG_PEEK));
print(f.recvfrom(10, MSG_PEEK));
Where the expected output should be the empty string twice.
Instead, make sk_peek_offset return negative values, and pass those values
to __skb_try_recv_datagram/__skb_try_recv_from_queue. If the passed offset
to __skb_try_recv_from_queue is negative, the checked skb is never skipped.
__skb_try_recv_from_queue will then ensure the offset is reset back to 0
if a peek is requested without an offset, unless no packets are found.
Also simplify the if condition in __skb_try_recv_from_queue. If _off is
greater then 0, and off is greater then or equal to skb->len, then
(_off || skb->len) must always be true assuming skb->len >= 0 is always
true.
Also remove a redundant check around a call to sk_peek_offset in af_unix.c,
as it double checked if MSG_PEEK was set in the flags.
V2:
- Moved the negative fixup into __skb_try_recv_from_queue, and remove now
redundant checks
- Fix peeking in udp{,v6}_recvmsg to report the right value when the
offset is 0
V3:
- Marked new branch in __skb_try_recv_from_queue as unlikely.
Signed-off-by: Matthew Dawson <matthew@mjdsystems.ca>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core/datagram.c')
-rw-r--r-- | net/core/datagram.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/net/core/datagram.c b/net/core/datagram.c index ee5647b..a21ca8d 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -169,14 +169,20 @@ struct sk_buff *__skb_try_recv_from_queue(struct sock *sk, int *peeked, int *off, int *err, struct sk_buff **last) { + bool peek_at_off = false; struct sk_buff *skb; - int _off = *off; + int _off = 0; + + if (unlikely(flags & MSG_PEEK && *off >= 0)) { + peek_at_off = true; + _off = *off; + } *last = queue->prev; skb_queue_walk(queue, skb) { if (flags & MSG_PEEK) { - if (_off >= skb->len && (skb->len || _off || - skb->peeked)) { + if (peek_at_off && _off >= skb->len && + (_off || skb->peeked)) { _off -= skb->len; continue; } |