linux/net/sctp
David Howells cdfbabfb2f net: Work around lockdep limitation in sockets that use sockets
Lockdep issues a circular dependency warning when AFS issues an operation
through AF_RXRPC from a context in which the VFS/VM holds the mmap_sem.

The theory lockdep comes up with is as follows:

 (1) If the pagefault handler decides it needs to read pages from AFS, it
     calls AFS with mmap_sem held and AFS begins an AF_RXRPC call, but
     creating a call requires the socket lock:

	mmap_sem must be taken before sk_lock-AF_RXRPC

 (2) afs_open_socket() opens an AF_RXRPC socket and binds it.  rxrpc_bind()
     binds the underlying UDP socket whilst holding its socket lock.
     inet_bind() takes its own socket lock:

	sk_lock-AF_RXRPC must be taken before sk_lock-AF_INET

 (3) Reading from a TCP socket into a userspace buffer might cause a fault
     and thus cause the kernel to take the mmap_sem, but the TCP socket is
     locked whilst doing this:

	sk_lock-AF_INET must be taken before mmap_sem

However, lockdep's theory is wrong in this instance because it deals only
with lock classes and not individual locks.  The AF_INET lock in (2) isn't
really equivalent to the AF_INET lock in (3) as the former deals with a
socket entirely internal to the kernel that never sees userspace.  This is
a limitation in the design of lockdep.

Fix the general case by:

 (1) Double up all the locking keys used in sockets so that one set are
     used if the socket is created by userspace and the other set is used
     if the socket is created by the kernel.

 (2) Store the kern parameter passed to sk_alloc() in a variable in the
     sock struct (sk_kern_sock).  This informs sock_lock_init(),
     sock_init_data() and sk_clone_lock() as to the lock keys to be used.

     Note that the child created by sk_clone_lock() inherits the parent's
     kern setting.

 (3) Add a 'kern' parameter to ->accept() that is analogous to the one
     passed in to ->create() that distinguishes whether kernel_accept() or
     sys_accept4() was the caller and can be passed to sk_alloc().

     Note that a lot of accept functions merely dequeue an already
     allocated socket.  I haven't touched these as the new socket already
     exists before we get the parameter.

     Note also that there are a couple of places where I've made the accepted
     socket unconditionally kernel-based:

	irda_accept()
	rds_rcp_accept_one()
	tcp_accept_from_sock()

     because they follow a sock_create_kern() and accept off of that.

Whilst creating this, I noticed that lustre and ocfs don't create sockets
through sock_create_kern() and thus they aren't marked as for-kernel,
though they appear to be internal.  I wonder if these should do that so
that they use the new set of lock keys.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2017-03-09 18:23:27 -08:00
..
associola.c sctp: add dst_pending_confirm flag 2017-02-07 13:07:46 -05:00
auth.c sctp: use IS_ENABLED() instead of checking for built-in or module 2016-09-10 21:19:11 -07:00
bind_addr.c sctp: not copying duplicate addrs to the assoc's bind address list 2016-12-20 14:15:45 -05:00
chunk.c sctp: refactor sctp_datamsg_from_user 2016-12-29 14:44:03 -05:00
debug.c net: sctp: fix array overrun read on sctp_timer_tbl 2017-01-24 15:24:35 -05:00
endpointola.c sctp: add reconf_enable in asoc ep and netns 2017-01-18 14:55:10 -05:00
input.c sctp: call rcu_read_lock before checking for duplicate transport nodes 2017-03-01 09:50:58 -08:00
inqueue.c sctp: rename WORD_TRUNC/ROUND macros 2016-09-22 03:13:26 -04:00
ipv6.c net: Work around lockdep limitation in sockets that use sockets 2017-03-09 18:23:27 -08:00
Kconfig sctp: add the sctp_diag.c file 2016-04-15 17:29:36 -04:00
Makefile sctp: prepare asoc stream for stream reconf 2017-01-06 21:07:26 -05:00
objcnt.c sctp: prepare asoc stream for stream reconf 2017-01-06 21:07:26 -05:00
offload.c sctp: sctp gso should set feature with NETIF_F_SG when calling skb_segment 2017-01-25 12:28:33 -05:00
output.c lib/vsprintf.c: remove %Z support 2017-02-27 18:43:47 -08:00
outqueue.c sctp: add dst_pending_confirm flag 2017-02-07 13:07:46 -05:00
primitive.c sctp: add stream reconf primitive 2017-01-18 14:55:10 -05:00
probe.c net: sctp: Convert log timestamps to be y2038 safe 2016-03-01 17:18:44 -05:00
proc.c net: Suppress the "Comparison to NULL could be written" warnings 2016-09-30 01:50:45 -04:00
protocol.c net: Work around lockdep limitation in sockets that use sockets 2017-03-09 18:23:27 -08:00
sctp_diag.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-10-02 22:20:41 -04:00
sm_make_chunk.c sctp: add a function to verify the sctp reconf chunk 2017-02-19 18:17:59 -05:00
sm_sideeffect.c sctp: flush out queue once assoc state falls into SHUTDOWN_PENDING 2017-02-20 10:26:09 -05:00
sm_statefuns.c sctp: add reconf chunk process 2017-02-19 18:17:59 -05:00
sm_statetable.c sctp: add reconf chunk event 2017-02-19 18:17:59 -05:00
socket.c net: Work around lockdep limitation in sockets that use sockets 2017-03-09 18:23:27 -08:00
stream.c sctp: implement receiver-side procedures for the Incoming SSN Reset Request Parameter 2017-02-19 18:17:59 -05:00
sysctl.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-01-11 23:55:43 -05:00
transport.c scripts/spelling.txt: add "varible" pattern and fix typo instances 2017-02-27 18:43:47 -08:00
tsnmap.c sctp: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
ulpevent.c sctp: add support for generating stream ssn reset event notification 2017-02-19 18:17:59 -05:00
ulpqueue.c sctp: prepare asoc stream for stream reconf 2017-01-06 21:07:26 -05:00