'buffer' string is copied from userspace.  It is not checked whether it is
zero terminated.  This may lead to overflow inside of simple_strtoul().
Changli Gao suggested to copy not more than user supplied 'size' bytes.

It was introduced before the git epoch.  Files "ipt_CLUSTERIP/*" are
root writable only by default, however, on some setups permissions might be
relaxed to e.g. network admin user.
Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

commit f3c5c1bf (make ip_tables reentrant) introduced a race in
handling the stackptr restore, at the end of ipt_do_table()

We should do it before the call to xt_info_rdunlock_bh(), or we allow
cpu preemption and another cpu overwrites stackptr of original one.

A second fix is to change the underflow test to check the origptr value
instead of 0 to detect underflow, or else we allow a jump from different
hooks.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

The revision of the set type was not checked at the create command: if the
userspace sent a valid set type but with not supported revision number,
it'd create a loop.
Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>

The hash:*port* types with IPv4 silently ignored when address ranges
with non TCP/UDP were added/deleted from the set and used the first
address from the range only.
Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>

When the OF device driver bits were converted over to the platform
device infrastructure in commit 74888760
("dt/net: Eliminate users of of_platform_{,un}register_driver") we
inadvertantly created probing problems in the OF case.

The NIU driver creates a dummy platform device to represent the
board that contains one or more child NIU devices.  Unfortunately
we use the same name, "niu", as the OF device driver itself uses.

The result is that we try to probe the dummy "niu" parent device we
create, and since it has a NULL ofdevice pointer etc. everything
explodes:

[783019.128243] niu: niu.c:v1.1 (Apr 22, 2010)
[783019.128810] Unable to handle kernel NULL pointer dereference
[783019.128949] tsk->{mm,active_mm}->context = 000000000000039e
[783019.129078] tsk->{mm,active_mm}->pgd = fffff803afc5a000
[783019.129206]               \|/ ____ \|/
[783019.129213]               "@'/ .. \`@"
[783019.129220]               /_| \__/ |_\
[783019.129226]                  \__U_/
[783019.129378] modprobe(2004): Oops [#1]
[783019.129423] TSTATE: 0000000011001602 TPC: 0000000010052ff8 TNPC: 000000000061bbb4 Y: 00000000    Not tainted
[783019.129542] TPC: <niu_of_probe+0x3c/0x2dc [niu]>
[783019.129624] g0: 8080000000000000 g1: 0000000000000000 g2: 0000000010056000 g3: 0000000000000002
[783019.129733] g4: fffff803fc1da0c0 g5: fffff800441e2000 g6: fffff803fba84000 g7: 0000000000000000
[783019.129842] o0: fffff803fe7df010 o1: 0000000010055700 o2: 0000000000000000 o3: fffff803fbacaca0
[783019.129951] o4: 0000000000000080 o5: 0000000000777908 sp: fffff803fba866e1 ret_pc: 0000000010052ff4
[783019.130083] RPC: <niu_of_probe+0x38/0x2dc [niu]>
[783019.130165] l0: fffff803fe7df010 l1: fffff803fbacafc0 l2: fffff803fbacaca0 l3: ffffffffffffffed
[783019.130273] l4: 0000000000000000 l5: 000000007fffffff l6: fffff803fba86f40 l7: 0000000000000001
[783019.130382] i0: fffff803fe7df000 i1: fffff803fc20aba0 i2: 0000000000000000 i3: 0000000000000001
[783019.130490] i4: 0000000000000000 i5: 0000000000000000 i6: fffff803fba867a1 i7: 000000000062038c
[783019.130614] I7: <platform_drv_probe+0xc/0x20>

Fix by simply renaming the parent device to "niu-board".
Signed-off-by: David S. Miller <davem@davemloft.net>

commit 54405cde (r8169: support control of advertising.)
introduced a bug in rtl8169_init_phy()
Reported-by: Piotr Hosowicz <piotr@hosowicz.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Oliver Neukum <oliver@neukum.org>
Cc: Francois Romieu <romieu@fr.zoreil.com>
Tested-by: Anca Emanuel <anca.emanuel@gmail.com>
Tested-by: Piotr Hosowicz <piotr@hosowicz.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

The calculation is off-by-one.  It should be "end - start + 1".  This
patch fixes it to use resource_size() instead.  Oddly, the code already
uses resource size correctly a couple lines earlier when it calls
request_mem_region() for this memory.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Now that we finally have __aligned_xx exported to userspace, convert
the headers that get exported over to the proper type.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Whenever we enter the IP stack proper from bridge netfilter we
need to ensure that the skb is in a form the IP stack expects
it to be in.

The entry point on NF_FORWARD did not meet the requirements of
the IP stack, therefore leading to potential crashes/panics.

This patch fixes the problem.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Commit c95b819a (gre: Use needed_headroom)
made gre use needed_headroom instead of hard_header_len

This uncover a bug in vlan code.

We should make sure vlan devices take into account their
real_dev->needed_headroom or we risk a crash in ipgre_header(), because
we dont have enough room to push IP header in skb.
Reported-by: Diddi Oscarsson <diddi@diddi.se>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

This structure was accidentally defined such that its layout can
differ between 32-bit and 64-bit processes.  Add compat structure
definitions and an ioctl wrapper function.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: stable@kernel.org [2.6.30+]
Signed-off-by: David S. Miller <davem@davemloft.net>

__ethtool_set_sg does not check if dev->ethtool_ops->set_sg is defined
which can result in a NULL pointer dereference when ethtool is used to
change SG settings for drivers without SG support.
Signed-off-by: Roger Luethi <rl@hellgate.ch>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

struct aunhdr has 4 padding bytes between 'pad' and 'handle' fields on
x86_64.  These bytes are not initialized in the variable 'ah' before
sending 'ah' to the network.  This leads to 4 bytes kernel stack
infoleak.

This bug was introduced before the git epoch.
Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Phil Blundell <philb@gnu.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

As specified by errata eTSEC49 of MPC8548 and errata eTSEC12 of MPC83xx,
older revisions of gianfar controllers will be unable to calculate a TCP/UDP
packet checksum for some alignments of the appropriate FCB. This patch checks
for FCB alignment on such controllers and falls back to software checksumming
if the alignment is known to be bad.
Signed-off-by: Alex Dubov <oakad@yahoo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

* 'linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci-2.6:
  PCI: label: remove #include of ACPI header to avoid warnings
  PCI: label: Fix compilation error when CONFIG_ACPI is unset
  PCI: pre-allocate additional resources to devices only after successful allocation of essential resources.
  PCI: introduce reset_resource()
  PCI: data structure agnostic free list function
  PCI: refactor io size calculation code
  PCI: do not create quirk I/O regions below PCIBIOS_MIN_IO for ICH
  PCI hotplug: acpiphp: set current_state to D0 in register_slot
  PCI: Export ACPI _DSM provided firmware instance number and string name to sysfs
  PCI: add more checking to ICH region quirks
  PCI: aer-inject: Override PCIe AER Mask Registers
  PCI: fix tlan build when CONFIG_PCI is not enabled
  PCI: remove quirk for pre-production systems
  PCI: Avoid potential NULL pointer dereference in pci_scan_bridge
  PCI/lpc: irq and pci_ids patch for Intel DH89xxCC DeviceIDs
  PCI: sysfs: Fix failure path for addition of "vpd" attribute

* 'spi/next' of git://git.secretlab.ca/git/linux-2.6: (34 commits)
  spi/dw_spi: move dw_spi.h into drivers/spi
  spi/dw_spi: Fix missing header
  gpio/langwell: Clear edge bit before handling
  gpio/langwell: Simplify demux loop
  gpio/langwell: Convert irq name space
  gpio/langwell: Fix broken irq_eoi change.
  gpio; Make Intel chipset gpio drivers depend on x86
  gpio/cs5535-gpio: Fix section mismatch
  spi/rtc-{ds1390,ds3234,m41t94}: Use spi_get_drvdata() for SPI devices
  spi/davinci: Support DMA transfers larger than 65535 words
  spi/davinci: Use correct length parameter to dma_map_single calls
  gpio: Use __devexit at necessary places
  gpio: add MODULE_DEVICE_TABLE to pch_gpio and ml_ioh_gpio
  gpio/mcp23s08: support mcp23s17 variant
  of_mmc_spi: add card detect irq support
  spi/omap_mcspi: catch xfers of non-multiple SPI word size
  spi/omap_mcspi: Off-by-one error in finding the right divisor
  gpio/pca953x: Fix wrong pointer type
  spi/pl022: rid dangling labels
  spi: add support for SuperH SPI
  ...

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/teigland/dlm:
  dlm: use alloc_workqueue function
  dlm: increase default hash table sizes
  dlm: record full callback state

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6:
  fs: call security_d_instantiate in d_obtain_alias V2
  lose 'mounting_here' argument in ->d_manage()
  don't pass 'mounting_here' flag to follow_down()
  change the locking order for namespace_sem
  fix deadlock in pivot_root()
  vfs: split off vfsmount-related parts of vfs_kern_mount()
  Some fixes for pstore
  kill simple_set_mnt()

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/bcopeland/omfs:
  omfs: make readdir stop when filldir says so
  omfs: merge unlink() and rmdir(), close leak in rename()
  omfs: stop playing silly buggers with omfs_unlink() in ->rename()
  omfs: rename() needs to mark old_inode dirty after ctime update

* 'linux-next' of git://git.infradead.org/ubifs-2.6: (25 commits)
  UBIFS: clean-up commentaries
  UBIFS: save 128KiB or more RAM
  UBIFS: allocate orphans scan buffer on demand
  UBIFS: allocate lpt dump buffer on demand
  UBIFS: allocate ltab checking buffer on demand
  UBIFS: allocate scanning buffer on demand
  UBIFS: allocate dump buffer on demand
  UBIFS: do not check data crc by default
  UBIFS: simplify UBIFS Kconfig menu
  UBIFS: print max. index node size
  UBIFS: handle allocation failures in UBIFS write path
  UBIFS: use max_write_size during recovery
  UBIFS: use max_write_size for write-buffers
  UBIFS: introduce write-buffer size field
  UBI: incorporate LEB offset information
  UBIFS: incorporate maximum write size
  UBI: provide LEB offset information
  UBI: incorporate maximum write size
  UBIFS: fix LEB number in printk
  UBIFS: restrict world-writable debugfs files
  ...

* 'linux-next' of git://git.infradead.org/ubi-2.6:
  UBI: make tests modes dynamic
  UBI: make self-checks dynamic
  UBI: make debugging messages dynamic
  UBI: remove UBI_IO_DEBUG macro
  UBI: kill debugging buffer
  UBI: allocate erase checking buffer on demand
  UBI: allocate write checking buffer on demand
  UBI: always re-read in case of read failures
  UBI: cleanup comments about corrupted PEBs
  UBI: add slab cache for ubi_scan_leb objects
  UBI: use raw mtd read function in debugging code
  UBI: try to reveal buggy MTD drivers
  UBI: add a commentary about allocating VID header buffer on stack
  UBI: cleanup LEB start calculations
  UBI: fix NOR erase preparation quirk

Add an entry for serial maintainers.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6: (308 commits)
  ALSA: sound/pci/asihpi: check adapter index in hpi_ioctl
  ALSA: aloop - Fix possible IRQ lock inversion
  ALSA: sound/core: merge list_del()/list_add_tail() to list_move_tail()
  ALSA: ctxfi - use list_move() instead of list_del()/list_add() combination
  ALSA: firewire - msleep needs delay.h
  ALSA: firewire-lib, firewire-speakers: handle packet queueing errors
  ALSA: firewire-lib: allocate DMA buffer separately
  ALSA: firewire-lib: use no-info SYT for packets without SYT sample
  ALSA: add LaCie FireWire Speakers/Griffin FireWave Surround driver
  ALSA: hda - Remove an unused variable in patch_realtek.c
  ALSA: hda - pin-adc-mux-dmic auto-configuration of 92HD8X codecs
  ALSA: hda - fix digital mic selection in mixer on 92HD8X codecs
  ALSA: hda - Move default input-src selection to init part
  ALSA: hda - Initialize special cases for input src in init phase
  ALSA: ctxfi - Clear input settings before initialization
  ALSA: ctxfi - Fix SPDIF status retrieval
  ALSA: ctxfi - Fix incorrect SPDIF status bit mask
  ALSA: ctxfi - Fix microphone boost codes/comments
  ALSA: atiixp - Fix wrong time-out checks during ac-link reset
  ALSA: intel8x0m: append 'm' to "r_intel8x0"
  ...

Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86: Flush TLB if PGD entry is changed in i386 PAE mode
  x86, dumpstack: Correct stack dump info when frame pointer is available
  x86: Clean up csum-copy_64.S a bit
  x86: Fix common misspellings
  x86: Fix misspelling and align params
  x86: Use PentiumPro-optimized partial_csum() on VIA C7

Merge branches 'irq-fixes-for-linus' and 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'irq-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  genirq: Fix incorrect unlock in __setup_irq()
  cris: Use generic show_interrupts()
  genirq: show_interrupts: Check desc->name before printing it blindly
  cris: Use accessor functions to set IRQ_PER_CPU flag
  cris: Fix irq conversion fallout

* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sched, kernel-doc: Fix runqueue_is_locked() description

Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (30 commits)
  trace, filters: Initialize the match variable in process_ops() properly
  trace, documentation: Fix branch profiling location in debugfs
  oprofile, s390: Cleanups
  oprofile, s390: Remove hwsampler_files.c and merge it into init.c
  perf: Fix tear-down of inherited group events
  perf: Reorder & optimize perf_event_context to remove alignment padding on 64 bit builds
  perf: Handle stopped state with tracepoints
  perf: Fix the software events state check
  perf, powerpc: Handle events that raise an exception without overflowing
  perf, x86: Use INTEL_*_CONSTRAINT() for all PEBS event constraints
  perf, x86: Clean up SandyBridge PEBS events
  perf lock: Fix sorting by wait_min
  perf tools: Version incorrect with some versions of grep
  perf evlist: New command to list the names of events present in a perf.data file
  perf script: Add support for H/W and S/W events
  perf script: Add support for dumping symbols
  perf script: Support custom field selection for output
  perf script: Move printing of 'common' data from print_event and rename
  perf tracing: Remove print_graph_cpu and print_graph_proc from trace-event-parse
  perf script: Change process_event prototype
  ...

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial: (47 commits)
  doc: CONFIG_UNEVICTABLE_LRU doesn't exist anymore
  Update cpuset info & webiste for cgroups
  dcdbas: force SMI to happen when expected
  arch/arm/Kconfig: remove one to many l's in the word.
  asm-generic/user.h: Fix spelling in comment
  drm: fix printk typo 'sracth'
  Remove one to many n's in a word
  Documentation/filesystems/romfs.txt: fixing link to genromfs
  drivers:scsi Change printk typo initate -> initiate
  serial, pch uart: Remove duplicate inclusion of linux/pci.h header
  fs/eventpoll.c: fix spelling
  mm: Fix out-of-date comments which refers non-existent functions
  drm: Fix printk typo 'failled'
  coh901318.c: Change initate to initiate.
  mbox-db5500.c Change initate to initiate.
  edac: correct i82975x error-info reported
  edac: correct i82975x mci initialisation
  edac: correct commented info
  fs: update comments to point correct document
  target: remove duplicate include of target/target_core_device.h from drivers/target/target_core_hba.c
  ...

Trivial conflict in fs/eventpoll.c (spelling vs addition)

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid: (48 commits)
  HID: add support for Logitech Driving Force Pro wheel
  HID: hid-ortek: remove spurious reference
  HID: add support for Ortek PKB-1700
  HID: roccat-koneplus: vorrect mode of sysfs attr 'sensor'
  HID: hid-ntrig: init settle and mode check
  HID: merge hid-egalax into hid-multitouch
  HID: hid-multitouch: Send events per slot if CONTACTCOUNT is missing
  HID: ntrig remove if and drop an indent
  HID: ACRUX - activate the device immediately after binding
  HID: ntrig: apply NO_INIT_REPORTS quirk
  HID: hid-magicmouse: Correct touch orientation direction
  HID: ntrig don't dereference unclaimed hidinput
  HID: Do not create input devices for feature reports
  HID: bt hidp: send Output reports using SET_REPORT on the Control channel
  HID: hid-sony.c: Fix sending Output reports to the Sixaxis
  HID: add support for Keytouch IEC 60945
  HID: Add HID Report Descriptor to sysfs
  HID: add IRTOUCH infrared USB to hid_have_special_driver
  HID: kernel oops in out_cleanup in function hidinput_connect
  HID: Add teletext/color keys - gyration remote - EU version (GYAR3101CKDE)
  ...

include/linux/dw_spi.h only includes driver internal data.  It doesn't
expose a platform_data configuration structure or similar (at least
nothing in-tree).  This patch moves the header into drivers/spi so
that the scope is limited to only the dw_spi_*.c driver files
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Feng Tang <feng.tang@intel.com>
Cc: spi-devel-general@lists.sourceforge.net

Currently, build on PPC dies with:
In file included from drivers/spi/dw_spi_mmio.c:16:
include/linux/spi/dw_spi.h:147: error: field ‘tx_sgl’ has incomplete type
include/linux/spi/dw_spi.h:149: error: field ‘rx_sgl’ has incomplete type

Add linux/scatterlist.h include to dw_spi.h, because we need to know
the contents of the structure.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

While trying to track down some NFS problems with BTRFS, I kept noticing I was
getting -EACCESS for no apparent reason.  Eric Paris and printk() helped me
figure out that it was SELinux that was giving me grief, with the following
denial

type=AVC msg=audit(1290013638.413:95): avc:  denied  { 0x800000 } for  pid=1772
comm="nfsd" name="" dev=sda1 ino=256 scontext=system_u:system_r:kernel_t:s0
tcontext=system_u:object_r:unlabeled_t:s0 tclass=file

Turns out this is because in d_obtain_alias if we can't find an alias we create
one and do all the normal instantiation stuff, but we don't do the
security_d_instantiate.

Usually we are protected from getting a hashed dentry that hasn't yet run
security_d_instantiate() by the parent's i_mutex, but obviously this isn't an
option there, so in order to deal with the case that a second thread comes in
and finds our new dentry before we get to run security_d_instantiate(), we go
ahead and call it if we find a dentry already.  Eric assures me that this is ok
as the code checks to see if the dentry has been initialized already so calling
security_d_instantiate() against the same dentry multiple times is ok.  With
this patch I'm no longer getting errant -EACCESS values.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

it's always false...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Make sure the 'match' variable always has a value.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

* 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc: (62 commits)
  powerpc/85xx: Fix signedness bug in cache-sram
  powerpc/fsl: 85xx: document cache sram bindings
  powerpc/fsl: define binding for fsl mpic interrupt controllers
  powerpc/fsl_msi: Handle msi-available-ranges better
  drivers/serial/ucc_uart.c: Add of_node_put to avoid memory leak
  powerpc/85xx: Fix SPE float to integer conversion failure
  powerpc/85xx: Update sata controller compatible for p1022ds board
  ATA: Add FSL sata v2 controller support
  powerpc/mpc8xxx_gpio: simplify searching for 'fsl, qoriq-gpio' compatiable
  powerpc/8xx: remove obsolete mgsuvd board
  powerpc/82xx: rename and update mgcoge board support
  powerpc/83xx: rename and update kmeter1
  powerpc/85xx: Workaroudn e500 CPU erratum A005
  powerpc/fsl_pci: Add support for FSL PCIe controllers v2.x
  powerpc/85xx: Fix writing to spin table 'cpu-release-addr' on ppc64e
  powerpc/pseries: Disable MSI using new interface if possible
  powerpc: Enable GENERIC_HARDIRQS_NO_DEPRECATED.
  powerpc: core irq_data conversion.
  powerpc: sysdev/xilinx_intc irq_data conversion.
  powerpc: sysdev/uic irq_data conversion.
  ...

Fix up conflicts in arch/powerpc/sysdev/fsl_msi.c (due to getting rid of
of_platform_driver in arch/powerpc)

it's always false now
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Have it nested inside ->i_mutex.  Instead of using follow_down()
under namespace_sem, followed by grabbing i_mutex and checking that
mountpoint to be is not dead, do the following:
	grab i_mutex
	check that it's not dead
	grab namespace_sem
	see if anything is mounted there
	if not, we've won
	otherwise
		drop locks
		put_path on what we had
		replace with what's mounted
		retry everything with new mountpoint to be

New helper (lock_mount()) does that.  do_add_mount(), do_move_mount(),
do_loopback() and pivot_root() switched to it; in case of the last
two that eliminates a race we used to have - original code didn't
do follow_down().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Don't hold vfsmount_lock over the loop traversing ->mnt_parent;
do check_mnt(new.mnt) under namespace_sem instead; combined with
namespace_sem held over all that code it'll guarantee the stability
of ->mnt_parent chain all the way to the root.

Doing check_mnt() outside of namespace_sem in case of pivot_root()
is wrong anyway.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>