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Subject[PATCH] mpt2sas: prevent double free on error path
I noticed this one when list_del was called with poisoned list
pointers, but the real problem is a double-free (and a use-after-free
just before that).

Both _scsih_probe_boot_devices() and _scsih_sas_device_add() put the
sas_device onto a list, thereby giving up control. Next they call
mpt2sas_transport_port_add() and will list_del and free the object on
errors. If some other function already did the list_del and free, it
will happen again.

This patch adds reference counting to prevent the double free. One
reference count goes to the caller of mpt2sas_transport_port_add(), the
second to the list. Whoever removes the object from the list gets to
drop one reference count. _scsih_probe_boot_devices() and
_scsih_sas_device_add() get a second reference count to ensure the
object is not freed while they are still accessing it.

To prevent the double list_del(), I changed the code to list_del_init()
and added a list_empty() check before that. Since the
list_empty/list_del_init is always called under a lock, this should be
safe.

I hate the complexity this patch adds, but see no alternative to it.

mpt2sas0: failure at drivers/scsi/mpt2sas/mpt2sas_transport.c:708/mpt2sas_transport_port_add()!
general protection fault: 0000 [#1] SMP
CPU 9
Pid: 3097, comm: kworker/u:11 Tainted: G W O 3.6.10+ #31392.trunk /0JP31P
RIP: 0010:[<ffffffffa0309744>] [<ffffffffa0309744>] _scsih_sas_device_remove+0x54/0x90 [mpt2sas]
RSP: 0018:ffff881fed4d7ab0 EFLAGS: 00010046
RAX: dead000000200200 RBX: ffff881ff6a5cd88 RCX: 00000000000010e8
RDX: ffff881ff7dab800 RSI: ffff881ff7daba00 RDI: dead000000100100
RBP: ffff881fed4d7ad0 R08: dead000000200200 R09: ffff880fff802200
R10: ffffffffa0317980 R11: 0000000000000000 R12: ffff881ff7daba00
R13: 0000000000000286 R14: 500605ba006c9d09 R15: ffff881ff7daba00
FS: 0000000000000000(0000) GS:ffff88203fc80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007f8ac89ec458 CR3: 0000001ff4c5c000 CR4: 00000000000407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process kworker/u:11 (pid: 3097, threadinfo ffff881fed4d6000, task ffff881402f3d9c0)
Stack:
0000000000000401 ffff881ff6a5c6b0 0000000000000401 0000000000000016
ffff881fed4d7bb0 ffffffffa030f93e 0000000000000000 ffff881ff6a5cd88
0012000e0f000008 006c9d090002000b 00180009500605ba 0000040100000016
Call Trace:
[<ffffffffa030f93e>] _scsih_add_device.clone.32+0x2fe/0x420 [mpt2sas]
[<ffffffffa03126e5>] _scsih_sas_topology_change_event.clone.38+0x285/0x620 [mpt2sas]
[<ffffffff81078c90>] ? load_balance+0x100/0x7a0
[<ffffffffa0312a80>] ? _scsih_sas_topology_change_event.clone.38+0x620/0x620 [mpt2sas]
[<ffffffffa0312d8a>] _firmware_event_work+0x30a/0xfc0 [mpt2sas]
[<ffffffff810015cc>] ? __switch_to+0x14c/0x410
[<ffffffff8106dfdb>] ? finish_task_switch+0x4b/0xf0
[<ffffffffa0312a80>] ? _scsih_sas_topology_change_event.clone.38+0x620/0x620 [mpt2sas]
[<ffffffff8105bf40>] process_one_work+0x140/0x500
[<ffffffff8105d354>] worker_thread+0x194/0x510
[<ffffffff8106dfdb>] ? finish_task_switch+0x4b/0xf0
[<ffffffff8105d1c0>] ? manage_workers+0x320/0x320
[<ffffffff8106282e>] kthread+0x9e/0xb0
[<ffffffff815bef44>] kernel_thread_helper+0x4/0x10
[<ffffffff815b5e5d>] ? retint_restore_args+0x13/0x13
[<ffffffff81062790>] ? kthread_freezable_should_stop+0x70/0x70
[<ffffffff815bef40>] ? gs_change+0x13/0x13

Signed-off-by: Joern Engel <joern@logfs.org>
---
drivers/scsi/mpt2sas/mpt2sas_base.h | 1 +
drivers/scsi/mpt2sas/mpt2sas_scsih.c | 55 ++++++++++++++++++++++++++++------
2 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/drivers/scsi/mpt2sas/mpt2sas_base.h b/drivers/scsi/mpt2sas/mpt2sas_base.h
index 543d8d6..ceb7d41 100644
--- a/drivers/scsi/mpt2sas/mpt2sas_base.h
+++ b/drivers/scsi/mpt2sas/mpt2sas_base.h
@@ -367,6 +367,7 @@ struct _sas_device {
u16 slot;
u8 phy;
u8 responding;
+ struct kref kref;
};

/**
diff --git a/drivers/scsi/mpt2sas/mpt2sas_scsih.c b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
index c6bdc92..43b3a98 100644
--- a/drivers/scsi/mpt2sas/mpt2sas_scsih.c
+++ b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
@@ -570,6 +570,18 @@ _scsih_sas_device_find_by_handle(struct MPT2SAS_ADAPTER *ioc, u16 handle)
return NULL;
}

+static void free_sas_device(struct kref *kref)
+{
+ struct _sas_device *sas_device = container_of(kref, struct _sas_device,
+ kref);
+ kfree(sas_device);
+}
+
+static void put_sas_device(struct _sas_device *sas_device)
+{
+ kref_put(&sas_device->kref, free_sas_device);
+}
+
/**
* _scsih_sas_device_remove - remove sas_device from list.
* @ioc: per adapter object
@@ -583,14 +595,19 @@ _scsih_sas_device_remove(struct MPT2SAS_ADAPTER *ioc,
struct _sas_device *sas_device)
{
unsigned long flags;
+ int was_on_list = 0;

if (!sas_device)
return;

spin_lock_irqsave(&ioc->sas_device_lock, flags);
- list_del(&sas_device->list);
- kfree(sas_device);
+ if (!list_empty(&sas_device->list)) {
+ list_del_init(&sas_device->list);
+ was_on_list = 1;
+ }
spin_unlock_irqrestore(&ioc->sas_device_lock, flags);
+ if (was_on_list)
+ put_sas_device(sas_device);
}


@@ -613,6 +630,8 @@ _scsih_sas_device_add(struct MPT2SAS_ADAPTER *ioc,
sas_device->handle, (unsigned long long)sas_device->sas_address));

spin_lock_irqsave(&ioc->sas_device_lock, flags);
+ /* Get an extra refcount... */
+ kref_get(&sas_device->kref);
list_add_tail(&sas_device->list, &ioc->sas_device_list);
spin_unlock_irqrestore(&ioc->sas_device_lock, flags);

@@ -630,6 +649,12 @@ _scsih_sas_device_add(struct MPT2SAS_ADAPTER *ioc,
sas_device->sas_address_parent);
_scsih_sas_device_remove(ioc, sas_device);
}
+ /*
+ * ...and drop it again. If an error already happend, this is the
+ * final put and we free the object now. Otherwise whoever removes
+ * the object from the list will do the final put and free.
+ */
+ put_sas_device(sas_device);
}

/**
@@ -5270,6 +5295,7 @@ _scsih_add_device(struct MPT2SAS_ADAPTER *ioc, u16 handle, u8 phy_num, u8 is_pd)
return -1;
}

+ kref_init(&sas_device->kref);
sas_device->handle = handle;
if (_scsih_get_sas_address(ioc, le16_to_cpu
(sas_device_pg0.ParentDevHandle),
@@ -5341,7 +5367,7 @@ _scsih_remove_device(struct MPT2SAS_ADAPTER *ioc,
"handle(0x%04x), sas_addr(0x%016llx)\n", ioc->name, __func__,
sas_device->handle, (unsigned long long)
sas_device->sas_address));
- kfree(sas_device);
+ put_sas_device(sas_device);
}
/**
* _scsih_device_remove_by_handle - removing device object by handle
@@ -5355,16 +5381,21 @@ _scsih_device_remove_by_handle(struct MPT2SAS_ADAPTER *ioc, u16 handle)
{
struct _sas_device *sas_device;
unsigned long flags;
+ int was_on_list = 0;

if (ioc->shost_recovery)
return;

spin_lock_irqsave(&ioc->sas_device_lock, flags);
sas_device = _scsih_sas_device_find_by_handle(ioc, handle);
- if (sas_device)
- list_del(&sas_device->list);
+ if (sas_device) {
+ if (!list_empty(&sas_device->list)) {
+ list_del_init(&sas_device->list);
+ was_on_list = 1;
+ }
+ }
spin_unlock_irqrestore(&ioc->sas_device_lock, flags);
- if (sas_device)
+ if (was_on_list)
_scsih_remove_device(ioc, sas_device);
}

@@ -5381,6 +5412,7 @@ mpt2sas_device_remove_by_sas_address(struct MPT2SAS_ADAPTER *ioc,
{
struct _sas_device *sas_device;
unsigned long flags;
+ int was_on_list = 0;

if (ioc->shost_recovery)
return;
@@ -5388,10 +5420,14 @@ mpt2sas_device_remove_by_sas_address(struct MPT2SAS_ADAPTER *ioc,
spin_lock_irqsave(&ioc->sas_device_lock, flags);
sas_device = mpt2sas_scsih_sas_device_find_by_sas_address(ioc,
sas_address);
- if (sas_device)
- list_del(&sas_device->list);
+ if (sas_device) {
+ if (!list_empty(&sas_device->list)) {
+ list_del_init(&sas_device->list);
+ was_on_list = 1;
+ }
+ }
spin_unlock_irqrestore(&ioc->sas_device_lock, flags);
- if (sas_device)
+ if (was_on_list)
_scsih_remove_device(ioc, sas_device);
}
#ifdef CONFIG_SCSI_MPT2SAS_LOGGING
@@ -7805,6 +7841,7 @@ _scsih_probe_boot_devices(struct MPT2SAS_ADAPTER *ioc)
handle = sas_device->handle;
sas_address_parent = sas_device->sas_address_parent;
sas_address = sas_device->sas_address;
+ kref_get(&sas_device->kref);
list_move_tail(&sas_device->list, &ioc->sas_device_list);
spin_unlock_irqrestore(&ioc->sas_device_lock, flags);

--
1.7.10.4


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