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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Hillf Danton <hdanton@sina.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	syzbot+82defefbbd8527e1c2cb@syzkaller.appspotmail.com,
	Will Deacon <will@kernel.org>
Subject: [PATCH 4.14 01/39] chardev: Avoid potential use-after-free in chrdev_open()
Date: Tue, 14 Jan 2020 11:01:35 +0100
Message-ID: <20200114094336.790695214@linuxfoundation.org> (raw)
In-Reply-To: <20200114094336.210038037@linuxfoundation.org>

From: Will Deacon <will@kernel.org>

commit 68faa679b8be1a74e6663c21c3a9d25d32f1c079 upstream.

'chrdev_open()' calls 'cdev_get()' to obtain a reference to the
'struct cdev *' stashed in the 'i_cdev' field of the target inode
structure. If the pointer is NULL, then it is initialised lazily by
looking up the kobject in the 'cdev_map' and so the whole procedure is
protected by the 'cdev_lock' spinlock to serialise initialisation of
the shared pointer.

Unfortunately, it is possible for the initialising thread to fail *after*
installing the new pointer, for example if the subsequent '->open()' call
on the file fails. In this case, 'cdev_put()' is called, the reference
count on the kobject is dropped and, if nobody else has taken a reference,
the release function is called which finally clears 'inode->i_cdev' from
'cdev_purge()' before potentially freeing the object. The problem here
is that a racing thread can happily take the 'cdev_lock' and see the
non-NULL pointer in the inode, which can result in a refcount increment
from zero and a warning:

  |  ------------[ cut here ]------------
  |  refcount_t: addition on 0; use-after-free.
  |  WARNING: CPU: 2 PID: 6385 at lib/refcount.c:25 refcount_warn_saturate+0x6d/0xf0
  |  Modules linked in:
  |  CPU: 2 PID: 6385 Comm: repro Not tainted 5.5.0-rc2+ #22
  |  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
  |  RIP: 0010:refcount_warn_saturate+0x6d/0xf0
  |  Code: 05 55 9a 15 01 01 e8 9d aa c8 ff 0f 0b c3 80 3d 45 9a 15 01 00 75 ce 48 c7 c7 00 9c 62 b3 c6 08
  |  RSP: 0018:ffffb524c1b9bc70 EFLAGS: 00010282
  |  RAX: 0000000000000000 RBX: ffff9e9da1f71390 RCX: 0000000000000000
  |  RDX: ffff9e9dbbd27618 RSI: ffff9e9dbbd18798 RDI: ffff9e9dbbd18798
  |  RBP: 0000000000000000 R08: 000000000000095f R09: 0000000000000039
  |  R10: 0000000000000000 R11: ffffb524c1b9bb20 R12: ffff9e9da1e8c700
  |  R13: ffffffffb25ee8b0 R14: 0000000000000000 R15: ffff9e9da1e8c700
  |  FS:  00007f3b87d26700(0000) GS:ffff9e9dbbd00000(0000) knlGS:0000000000000000
  |  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  |  CR2: 00007fc16909c000 CR3: 000000012df9c000 CR4: 00000000000006e0
  |  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  |  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  |  Call Trace:
  |   kobject_get+0x5c/0x60
  |   cdev_get+0x2b/0x60
  |   chrdev_open+0x55/0x220
  |   ? cdev_put.part.3+0x20/0x20
  |   do_dentry_open+0x13a/0x390
  |   path_openat+0x2c8/0x1470
  |   do_filp_open+0x93/0x100
  |   ? selinux_file_ioctl+0x17f/0x220
  |   do_sys_open+0x186/0x220
  |   do_syscall_64+0x48/0x150
  |   entry_SYSCALL_64_after_hwframe+0x44/0xa9
  |  RIP: 0033:0x7f3b87efcd0e
  |  Code: 89 54 24 08 e8 a3 f4 ff ff 8b 74 24 0c 48 8b 3c 24 41 89 c0 44 8b 54 24 08 b8 01 01 00 00 89 f4
  |  RSP: 002b:00007f3b87d259f0 EFLAGS: 00000293 ORIG_RAX: 0000000000000101
  |  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3b87efcd0e
  |  RDX: 0000000000000000 RSI: 00007f3b87d25a80 RDI: 00000000ffffff9c
  |  RBP: 00007f3b87d25e90 R08: 0000000000000000 R09: 0000000000000000
  |  R10: 0000000000000000 R11: 0000000000000293 R12: 00007ffe188f504e
  |  R13: 00007ffe188f504f R14: 00007f3b87d26700 R15: 0000000000000000
  |  ---[ end trace 24f53ca58db8180a ]---

Since 'cdev_get()' can already fail to obtain a reference, simply move
it over to use 'kobject_get_unless_zero()' instead of 'kobject_get()',
which will cause the racing thread to return -ENXIO if the initialising
thread fails unexpectedly.

Cc: Hillf Danton <hdanton@sina.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: syzbot+82defefbbd8527e1c2cb@syzkaller.appspotmail.com
Signed-off-by: Will Deacon <will@kernel.org>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191219120203.32691-1-will@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/char_dev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -361,7 +361,7 @@ static struct kobject *cdev_get(struct c
 
 	if (owner && !try_module_get(owner))
 		return NULL;
-	kobj = kobject_get(&p->kobj);
+	kobj = kobject_get_unless_zero(&p->kobj);
 	if (!kobj)
 		module_put(owner);
 	return kobj;



  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14 10:01 [PATCH 4.14 00/39] 4.14.165-stable review Greg Kroah-Hartman
2020-01-14 10:01 ` Greg Kroah-Hartman [this message]
2020-01-14 10:01 ` [PATCH 4.14 02/39] usb: chipidea: host: Disable port power only if previously enabled Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 03/39] ALSA: usb-audio: Apply the sample rate quirk for Bose Companion 5 Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 04/39] ALSA: hda/realtek - Add new codec supported for ALCS1200A Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 05/39] ALSA: hda/realtek - Set EAPD control to default for ALC222 Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 06/39] kernel/trace: Fix do not unregister tracepoints when register sched_migrate_task fail Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 07/39] tracing: Have stack tracer compile when MCOUNT_INSN_SIZE is not defined Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 08/39] HID: Fix slab-out-of-bounds read in hid_field_extract Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 09/39] HID: uhid: Fix returning EPOLLOUT from uhid_char_poll Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 10/39] can: gs_usb: gs_usb_probe(): use descriptors of current altsetting Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 11/39] can: mscan: mscan_rx_poll(): fix rx path lockup when returning from polling to irq mode Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 12/39] can: can_dropped_invalid_skb(): ensure an initialized headroom in outgoing CAN sk_buffs Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 13/39] gpiolib: acpi: Turn dmi_system_id table into a generic quirk table Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 14/39] gpiolib: acpi: Add honor_wakeup module-option + quirk mechanism Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 15/39] staging: vt6656: set usb_set_intfdata on driver fail Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 16/39] USB: serial: option: add ZLP support for 0x1bc7/0x9010 Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 17/39] usb: musb: fix idling for suspend after disconnect interrupt Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 18/39] usb: musb: Disable pullup at init Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 19/39] usb: musb: dma: Correct parameter passed to IRQ handler Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 20/39] staging: comedi: adv_pci1710: fix AI channels 16-31 for PCI-1713 Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 21/39] HID: hid-input: clear unmapped usages Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 22/39] Input: add safety guards to input_set_keycode() Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 23/39] drm/fb-helper: Round up bits_per_pixel if possible Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 24/39] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ Greg Kroah-Hartman
2020-01-14 10:01 ` [PATCH 4.14 25/39] staging: rtl8188eu: Add device code for TP-Link TL-WN727N v5.21 Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 26/39] tty: link tty and port before configuring it as console Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 27/39] tty: always relink the port Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 28/39] mwifiex: fix possible heap overflow in mwifiex_process_country_ie() Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 29/39] mwifiex: pcie: Fix memory leak in mwifiex_pcie_alloc_cmdrsp_buf Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 30/39] scsi: bfa: release allocated memory in case of error Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 31/39] rtl8xxxu: prevent leaking urb Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 32/39] ath10k: fix memory leak Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 33/39] arm64: cpufeature: Avoid warnings due to unused symbols Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 34/39] HID: hiddev: fix mess in hiddev_open() Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 35/39] USB: Fix: Dont skip endpoint descriptors with maxpacket=0 Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 36/39] phy: cpcap-usb: Fix error path when no host driver is loaded Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 37/39] phy: cpcap-usb: Fix flakey host idling and enumerating of devices Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 38/39] netfilter: arp_tables: init netns pointer in xt_tgchk_param struct Greg Kroah-Hartman
2020-01-14 10:02 ` [PATCH 4.14 39/39] netfilter: ipset: avoid null deref when IPSET_ATTR_LINENO is present Greg Kroah-Hartman
2020-01-14 15:02 ` [PATCH 4.14 00/39] 4.14.165-stable review Jon Hunter
2020-01-14 18:15 ` Guenter Roeck
2020-01-14 20:27 ` shuah
2020-01-15  2:08 ` Daniel Díaz

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