path: root/net/unix
diff options
authorMatthew Dawson <matthew@mjdsystems.ca>2017-08-18 15:04:54 -0400
committerDavid S. Miller <davem@davemloft.net>2017-08-18 15:12:54 -0700
commita0917e0bc6efc05834c0c1eafebd579a9c75e6e9 (patch)
tree31f8b60d8e7a0a20943057d7345fdca3558e5ed8 /net/unix
parentbpf, doc: improve sysctl knob description (diff)
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/unix')
1 files changed, 1 insertions, 4 deletions
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 7b52a380d710..be8982b4f8c0 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2304,10 +2304,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
- if (flags & MSG_PEEK)
- skip = sk_peek_offset(sk, flags);
- else
- skip = 0;
+ skip = max(sk_peek_offset(sk, flags), 0);
do {
int chunk;