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authorDaniel Borkmann <dborkman@redhat.com>2013-12-06 14:36:15 +0400
committerDavid S. Miller <davem@davemloft.net>2013-12-10 05:09:20 +0400
commit66e56cd46b93ef407c60adcac62cf33b06119d50 (patch)
treed10e5ec58ce412c66700626e39fc363d87c71165 /Documentation/networking/packet_mmap.txt
parent98bfd23cdb30e68e90571d7a2607e9479f8a50ec (diff)
downloadlinux-66e56cd46b93ef407c60adcac62cf33b06119d50.tar.xz
packet: fix send path when running with proto == 0
Commit e40526cb20b5 introduced a cached dev pointer, that gets hooked into register_prot_hook(), __unregister_prot_hook() to update the device used for the send path. We need to fix this up, as otherwise this will not work with sockets created with protocol = 0, plus with sll_protocol = 0 passed via sockaddr_ll when doing the bind. So instead, assign the pointer directly. The compiler can inline these helper functions automagically. While at it, also assume the cached dev fast-path as likely(), and document this variant of socket creation as it seems it is not widely used (seems not even the author of TX_RING was aware of that in his reference example [1]). Tested with reproducer from e40526cb20b5. [1] http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap#Example Fixes: e40526cb20b5 ("packet: fix use after free race in send path when dev is released") Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Tested-by: Salam Noureddine <noureddine@aristanetworks.com> Tested-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/networking/packet_mmap.txt')
-rw-r--r--Documentation/networking/packet_mmap.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index c01223628a87..8e48e3b14227 100644
--- a/Documentation/networking/packet_mmap.txt
+++ b/Documentation/networking/packet_mmap.txt
@@ -123,6 +123,16 @@ Transmission process is similar to capture as shown below.
[shutdown] close() --------> destruction of the transmission socket and
deallocation of all associated resources.
+Socket creation and destruction is also straight forward, and is done
+the same way as in capturing described in the previous paragraph:
+
+ int fd = socket(PF_PACKET, mode, 0);
+
+The protocol can optionally be 0 in case we only want to transmit
+via this socket, which avoids an expensive call to packet_rcv().
+In this case, you also need to bind(2) the TX_RING with sll_protocol = 0
+set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example.
+
Binding the socket to your network interface is mandatory (with zero copy) to
know the header size of frames used in the circular buffer.