path: root/net/Kconfig
diff options
authorJohannes Berg <johannes@sipsolutions.net>2009-07-01 11:26:02 +0000
committerDavid S. Miller <davem@davemloft.net>2009-07-15 08:53:39 -0700
commit1dacc76d0014a034b8aca14237c127d7c19d7726 (patch)
treed3ba044578fab9076ef4a73694fa7d23d4a50969 /net/Kconfig
parent4f45b2cd4e78b5e49d7d41548345b879d3fdfeae (diff)
net/compat/wext: send different messages to compat tasks
Wireless extensions have the unfortunate problem that events are multicast netlink messages, and are not independent of pointer size. Thus, currently 32-bit tasks on 64-bit platforms cannot properly receive events and fail with all kinds of strange problems, for instance wpa_supplicant never notices disassociations, due to the way the 64-bit event looks (to a 32-bit process), the fact that the address is all zeroes is lost, it thinks instead it is 00:00:00:00:01:00. The same problem existed with the ioctls, until David Miller fixed those some time ago in an heroic effort. A different problem caused by this is that we cannot send the ASSOCREQIE/ASSOCRESPIE events because sending them causes a 32-bit wpa_supplicant on a 64-bit system to overwrite its internal information, which is worse than it not getting the information at all -- so we currently resort to sending a custom string event that it then parses. This, however, has a severe size limitation we are frequently hitting with modern access points; this limitation would can be lifted after this patch by sending the correct binary, not custom, event. A similar problem apparently happens for some other netlink users on x86_64 with 32-bit tasks due to the alignment for 64-bit quantities. In order to fix these problems, I have implemented a way to send compat messages to tasks. When sending an event, we send the non-compat event data together with a compat event data in skb_shinfo(main_skb)->frag_list. Then, when the event is read from the socket, the netlink code makes sure to pass out only the skb that is compatible with the task. This approach was suggested by David Miller, my original approach required always sending two skbs but that had various small problems. To determine whether compat is needed or not, I have used the MSG_CMSG_COMPAT flag, and adjusted the call path for recv and recvfrom to include it, even if those calls do not have a cmsg parameter. I have not solved one small part of the problem, and I don't think it is necessary to: if a 32-bit application uses read() rather than any form of recvmsg() it will still get the wrong (64-bit) event. However, neither do applications actually do this, nor would it be a regression. Signed-off-by: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/Kconfig')
1 files changed, 20 insertions, 0 deletions
diff --git a/net/Kconfig b/net/Kconfig
index 7051b9710675..041c35edb763 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -23,6 +23,26 @@ menuconfig NET
if NET
+ bool
+ help
+ This option can be selected by other options that need compat
+ netlink messages.
+ def_bool y
+ depends on COMPAT
+ help
+ This option makes it possible to send different netlink messages
+ to tasks depending on whether the task is a compat task or not. To
+ achieve this, you need to set skb_shinfo(skb)->frag_list to the
+ compat skb before sending the skb, the netlink code will sort out
+ which message to actually pass to the task.
+ Newly written code should NEVER need this option but do
+ compat-independent messages instead!
menu "Networking options"
source "net/packet/Kconfig"

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