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[PATCH 3.19.y-ckt 51/54] batman-adv: Reduce refcnt of removed router when updating route

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3.19.8-ckt21 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Sven Eckelmann <sven@narfation.org>

commit d1a65f1741bfd9c69f9e4e2ad447a89b6810427d upstream.

_batadv_update_route rcu_derefences orig_ifinfo->router outside of a
spinlock protected region to print some information messages to the debug
log. But this pointer is not checked again when the new pointer is assigned
in the spinlock protected region. Thus is can happen that the value of
orig_ifinfo->router changed in the meantime and thus the reference counter
of the wrong router gets reduced after the spinlock protected region.

Just rcu_dereferencing the value of orig_ifinfo->router inside the spinlock
protected region (which also set the new pointer) is enough to get the
correct old router object.

Fixes: e1a5382f978b ("batman-adv: Make orig_node->router an rcu protected pointer")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 net/batman-adv/routing.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 6648f32..7fe3d65 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -88,6 +88,15 @@ static void _batadv_update_route(struct batadv_priv *bat_priv,
 		neigh_node = NULL;
 
 	spin_lock_bh(&orig_node->neigh_list_lock);
+	/* curr_router used earlier may not be the current orig_ifinfo->router
+	 * anymore because it was dereferenced outside of the neigh_list_lock
+	 * protected region. After the new best neighbor has replace the current
+	 * best neighbor the reference counter needs to decrease. Consequently,
+	 * the code needs to ensure the curr_router variable contains a pointer
+	 * to the replaced best neighbor.
+	 */
+	curr_router = rcu_dereference_protected(orig_ifinfo->router, true);
+
 	rcu_assign_pointer(orig_ifinfo->router, neigh_node);
 	spin_unlock_bh(&orig_node->neigh_list_lock);
 	batadv_orig_ifinfo_free_ref(orig_ifinfo);
-- 
2.7.4

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[3.19.y-ckt stable] Linux 3.19.8-ckt21 stable review Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 42/54] x86/sysfb_efi: Fix valid BAR address range check Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 53/54] cxgbi: fix uninitialized flowi6 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 14/54] mm: split ET_DYN ASLR from mmap ASLR Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 51/54] batman-adv: Reduce refcnt of removed router when updating route Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 18/54] ASoC: dapm: Make sure we have a card when displaying component widgets Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 11/54] s390: standardize mmap_rnd() usage Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 04/54] arm: factor out mmap ASLR into mmap_rnd Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 52/54] batman-adv: Fix broadcast/ogm queue limit on a removed interface Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 31/54] ARM: SoCFPGA: Fix secondary CPU startup in thumb2 kernel Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 48/54] jme: Do not enable NIC WoL functions on S0 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 54/54] net/mlx4_en: fix spurious timestamping callbacks Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 12/54] mm: expose arch_mmap_rnd when available Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:10 +0200
  [PATCH 3.19.y-ckt 20/54] i2c: cpm: Fix build break due to incompatible pointer types Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 21/54] i2c: exynos5: Fix possible ABBA deadlock by keeping I2C clock prepared Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 37/54] Minimal fix-up of bad hashing behavior of hash_64() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 36/54] powerpc: Fix bad inline asm constraint in create_zero_mask() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 32/54] IB/security: Restrict use of the write() interface Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 24/54] USB: serial: cp210x: add Straizona Focusers device ids Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 09/54] s390: avoid z13 cache aliasing Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 34/54] mm: vmscan: reclaim highmem zone if buffer_heads is over limit Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 28/54] cxl: Keep IRQ mappings on context teardown Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 26/54] workqueue: fix ghost PENDING flag while doing MQ IO Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 27/54] drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 29/54] drm/i915: Fix system resume if PCI device remained enabled Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 08/54] powerpc: standardize mmap_rnd() usage Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 40/54] MAINTAINERS: Remove asterisk from EFI directory names Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 41/54] ACPICA: Dispatcher: Update thread ID for recursive method calls Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 47/54] parisc: fix a bug when syscall number of tracee is __NR_Linux_syscalls Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 25/54] ALSA: hda - Add dock support for ThinkPad X260 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 23/54] USB: serial: cp210x: add ID for Link ECU Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 13/54] s390: redefine randomize_et_dyn for ELF_ET_DYN_BASE Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 30/54] drm/i915/ddi: Fix eDP VDD handling during booting and suspend/resume Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 35/54] EDAC: i7core, sb_edac: Don't return NOTIFY_BAD from mce_decoder callback Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 06/54] arm64: standardize mmap_rnd() usage Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 43/54] fs/pnode.c: treat zero mnt_group_id-s as unequal Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 44/54] propogate_mnt: Handle the first propogated copy being a slave Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 33/54] mm/huge_memory: replace VM_NO_THP VM_BUG_ON with actual VMA check Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 10/54] s390/mm: align 64-bit PIE binaries to 4GB Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 17/54] ASoC: rt5640: Correct the digital interface data select Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 46/54] x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 39/54] drm/radeon: make sure vertical front porch is at least 1 Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 19/54] iio: ak8975: Fix NULL pointer exception on early interrupt Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:20 +0200
  [PATCH 3.19.y-ckt 07/54] mips: extract logic for mmap_rnd() Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:30 +0200
  [PATCH 3.19.y-ckt 01/54] [3.19-stable-only] Revert "powerpc: Update TM user feature bits in scan_features()" Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:30 +0200
    Re: [PATCH 3.19.y-ckt 01/54] [3.19-stable-only] Revert "powerpc:  Update TM user feature bits in scan_features()" Michael Ellerman <mpe@ellerman.id.au> - 2016-05-10 03:50 +0200
  [PATCH 3.19.y-ckt 02/54] [3.19-stable-only] fix backport "KVM: s390: avoid memory overwrites on emergency signal injection" Kamal Mostafa <kamal@canonical.com> - 2016-05-10 02:30 +0200

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