| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.17 026/122] ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg | Date | Fri, 5 Dec 2014 14:43:20 -0800 |
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3.17-stable review patch. If anyone has any objections, please let me know.
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From: Jiri Bohac <jbohac@suse.cz>
[ 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@suse.cz> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- 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; }
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