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[PATCH 4.4 08/56] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously

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

------------------

From: Ajay Kaher <ajay.kaher@samsung.com>

commit 2f86a96be0ccb1302b7eee7855dbee5ce4dc5dfb upstream.

There is race condition when two USB class drivers try to call
init_usb_class at the same time and leads to crash.
code path: probe->usb_register_dev->init_usb_class

To solve this, mutex locking has been added in init_usb_class() and
destroy_usb_class().

As pointed by Alan, removed "if (usb_class)" test from destroy_usb_class()
because usb_class can never be NULL there.

Signed-off-by: Ajay Kaher <ajay.kaher@samsung.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/core/file.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -26,6 +26,7 @@
 #define MAX_USB_MINORS	256
 static const struct file_operations *usb_minors[MAX_USB_MINORS];
 static DECLARE_RWSEM(minor_rwsem);
+static DEFINE_MUTEX(init_usb_class_mutex);
 
 static int usb_open(struct inode *inode, struct file *file)
 {
@@ -108,8 +109,9 @@ static void release_usb_class(struct kre
 
 static void destroy_usb_class(void)
 {
-	if (usb_class)
-		kref_put(&usb_class->kref, release_usb_class);
+	mutex_lock(&init_usb_class_mutex);
+	kref_put(&usb_class->kref, release_usb_class);
+	mutex_unlock(&init_usb_class_mutex);
 }
 
 int usb_major_init(void)
@@ -171,7 +173,10 @@ int usb_register_dev(struct usb_interfac
 	if (intf->minor >= 0)
 		return -EADDRINUSE;
 
+	mutex_lock(&init_usb_class_mutex);
 	retval = init_usb_class();
+	mutex_unlock(&init_usb_class_mutex);
+
 	if (retval)
 		return retval;
 

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[PATCH 4.4 00/56] 4.4.69-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 54/56] wlcore: Pass win_size taken from ieee80211_sta to FW Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 34/56] fs/xattr.c: zero out memory copied to userspace in getxattr Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 52/56] mac80211: pass block ack session timeout to to driver Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 42/56] padata: free correct variable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 56/56] ipmi: Fix kernel panic at ipmi_ssif_thread() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 17/56] usb: hub: Do not attempt to autosuspend disconnected devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 24/56] KVM: arm/arm64: fix races in kvm_psci_vcpu_on Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 09/56] staging: vt6656: use off stack for in buffer USB transfers. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 33/56] ext4: evict inline data when writing to memory map Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 51/56] mac80211: pass RX aggregation window size to driver Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 38/56] SMB3: Work around mount failure when using SMB3 dialect to Macs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 55/56] wlcore: Add RX_BA_WIN_SIZE_CHANGE_EVENT event Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 45/56] serial: omap: fix runtime-pm handling on unbind Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 03/56] target/fileio: Fix zero-length READ and WRITE handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 50/56] Bluetooth: hci_intel: add missing tty-device sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 46/56] serial: omap: suspend device on probe errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 28/56] vfio/type1: Remove locked page accounting workqueue Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 44/56] serial: samsung: Use right device for DMA-mapping calls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 36/56] fs/block_dev: always invalidate cleancache in invalidate_bdev() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 08/56] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 05/56] iscsi-target: Set session_fall_back_to_erl0 when forcing reinstatement Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 12/56] staging: comedi: jr3_pci: fix possible null pointer dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:10 +0200
  [PATCH 4.4 20/56] selftests/x86/ldt_gdt_32: Work around a glibc sigaction() bug Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 04/56] target: Convert ACL change queue_depth se_session reference usage Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 27/56] dm era: save spacemap metadata root after the pre-commit Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 22/56] um: Fix PTRACE_POKEUSER on x86_64 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 10/56] staging: vt6656: use off stack for out buffer USB transfers. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 18/56] usb: misc: legousbtower: Fix buffers on stack Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 14/56] usb: misc: add missing continue in switch Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 21/56] x86, pmem: Fix cache flushing for iovec write < 8 bytes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 16/56] usb: hub: Fix error loop seen after hub communication errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 15/56] usb: Make sure usb/phy/of gets built-in Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 11/56] staging: gdm724x: gdm_mux: fix use-after-free on module unload Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 29/56] IB/core: Fix sysfs registration error flow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 19/56] x86/boot: Fix BSS corruption/overwrite bug in early x86 kernel startup Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  [PATCH 4.4 25/56] block: fix blk_integrity_register to use templates interval_exp if not 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-18 13:20 +0200
  Re: [PATCH 4.4 00/56] 4.4.69-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-05-18 19:40 +0200
  Re: [PATCH 4.4 00/56] 4.4.69-stable review Guenter Roeck <linux@roeck-us.net> - 2017-05-19 03:20 +0200

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