This is a note to let you know that I've just added the patch titled
ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg
to the 3.17-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ipx-fix-locking-regression-in-ipx_sendmsg-and-ipx_recvmsg.patch
and it can be found in the queue-3.17 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Wed Dec 3 17:06:35 PST 2014
From: Jiri Bohac <jbohac@xxxxxxx>
Date: Wed, 19 Nov 2014 23:05:49 +0100
Subject: ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg
From: Jiri Bohac <jbohac@xxxxxxx>
[ Upstream commit 01462405f0c093b2f8dfddafcadcda6c9e4c5cdf ]
This fixes an old regression introduced by commit
b0d0d915 (ipx: remove the BKL).
When a recvmsg syscall blocks waiting for new data, no data can be sent on the
same socket with sendmsg because ipx_recvmsg() sleeps with the socket locked.
This breaks mars-nwe (NetWare emulator):
- the ncpserv process reads the request using recvmsg
- ncpserv forks and spawns nwconn
- ncpserv calls a (blocking) recvmsg and waits for new requests
- nwconn deadlocks in sendmsg on the same socket
Commit b0d0d915 has simply replaced BKL locking with
lock_sock/release_sock. Unlike now, BKL got unlocked while
sleeping, so a blocking recvmsg did not block a concurrent
sendmsg.
Only keep the socket locked while actually working with the socket data and
release it prior to calling skb_recv_datagram().
Signed-off-by: Jiri Bohac <jbohac@xxxxxxx>
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipx/af_ipx.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/net/ipx/af_ipx.c
+++ b/net/ipx/af_ipx.c
@@ -1764,6 +1764,7 @@ static int ipx_recvmsg(struct kiocb *ioc
struct ipxhdr *ipx = NULL;
struct sk_buff *skb;
int copied, rc;
+ bool locked = true;
lock_sock(sk);
/* put the autobinding in */
@@ -1790,6 +1791,8 @@ static int ipx_recvmsg(struct kiocb *ioc
if (sock_flag(sk, SOCK_ZAPPED))
goto out;
+ release_sock(sk);
+ locked = false;
skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
flags & MSG_DONTWAIT, &rc);
if (!skb) {
@@ -1826,7 +1829,8 @@ static int ipx_recvmsg(struct kiocb *ioc
out_free:
skb_free_datagram(sk, skb);
out:
- release_sock(sk);
+ if (locked)
+ release_sock(sk);
return rc;
}
Patches currently in stable-queue which might be from jbohac@xxxxxxx are
queue-3.17/ipx-fix-locking-regression-in-ipx_sendmsg-and-ipx_recvmsg.patch
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