[PATCH 0/3] firewire: use single object for user space listeners to dispatch request to IEC 61883-1 FCP region

From: Takashi Sakamoto
Date: Fri Jan 20 2023 - 04:04:05 EST

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Hi,

This patch solves long standing issue mentioned by code comment[1] and a
commit 281e20323ab7 ("firewire: core: fix use-after-free regression in FCP
handler")[2]. This patchset is based on the kernel tree to which another
fix is applied[3].

To Iwai-san, I would like to ask you picking them to your local
tree, then send them to mainline tree as well as sound patches when
the merge window is open for v6.3 kernel, unless any question and
objection is posted. (Additionally, I have prepared the other patchset for
the subsystem.)

Linux FireWire subsystem allows multiple listeners to inbound request to
IEC 61883-1 FCP region. The listeners need to access to the payload of
request, while the core function needs to guarantee transaction completion
by sending response. It is a risk to use-after-free by accessing to the
object of request released at completion.

The commit 281e20323ab7 solves the risk by the duplication of payload,
while it is slightly redundant (and a risk of memory leak[3]). Developers
have acknowledged that the advantage of reference count to maintain the
lifetime of object.

Furthermore, the commit uses NULL pointer for the listeners to
distinguish whether the request is to FCP region or not. It is a risk
that the listeners retrieve parameters by dereferencing it. For
instance, a commit b2405aa948b9 ("firewire: add kernel API to access
packet structure in request structure for AR context")[4] adds a kernel
API to retrieve time stamp from the data of request, while it is not
available in the case of request to FCP region.

As a solution, this patchset uses kref structure to maintain lifetime of
data for fw_request structure, then dismisses NULL pointer passing to the
listeners. Finally, the duplication is obsoleted.

This is a log to probe kmalloc/kfree tracepoints events in the case to
handle the request to FCP region.

irq/35-firewire-273881 [002] 373149.138580: kmalloc: (fw_core_handle_request+0x7b) call_site=fw_core_handle_request+0x7b ptr=0xffff99e93f007300 bytes_req=155 bytes_alloc=192 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138582: kmalloc: (handle_request+0x22e) call_site=handle_request+0x22e ptr=0xffff99e96e54f240 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138583: kmalloc: (handle_request+0x24b) call_site=handle_request+0x24b ptr=0xffff99e8b8a6ed20 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138587: kmalloc: (handle_request+0x22e) call_site=handle_request+0x22e ptr=0xffff99e96e54fa80 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138587: kmalloc: (handle_request+0x24b) call_site=handle_request+0x24b ptr=0xffff99e8a3f06960 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138591: kmalloc: (handle_request+0x22e) call_site=handle_request+0x22e ptr=0xffff99e96e54f380 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138591: kmalloc: (handle_request+0x24b) call_site=handle_request+0x24b ptr=0xffff99e8a3f06600 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138598: kmalloc: (handle_request+0x22e) call_site=handle_request+0x22e ptr=0xffff99e96e54f7c0 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138598: kmalloc: (handle_request+0x24b) call_site=handle_request+0x24b ptr=0xffff99e8a3f06180 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138602: kmalloc: (handle_request+0x22e) call_site=handle_request+0x22e ptr=0xffff99e96e54f4c0 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 373149.138603: kmalloc: (handle_request+0x24b) call_site=handle_request+0x24b ptr=0xffff99e94d48b660 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_ATOMIC
python3-278050 [000] 373149.138605: kfree: (fw_device_op_read+0x148) call_site=fw_device_op_read+0x148 ptr=0xffff99e8b8a6ed20
python3-278050 [000] 373149.138611: kfree: (ioctl_send_response+0x10a) call_site=ioctl_send_response+0x10a ptr=0xffff99e96e54f240
python3-278053 [001] 373149.138612: kfree: (fw_device_op_read+0x148) call_site=fw_device_op_read+0x148 ptr=0xffff99e8a3f06960
snd-oxfw-ctl-se-278061 [003] 373149.138618: kfree: (fw_device_op_read+0x148) call_site=fw_device_op_read+0x148 ptr=0xffff99e94d48b660
python3-278053 [001] 373149.138621: kfree: (ioctl_send_response+0x10a) call_site=ioctl_send_response+0x10a ptr=0xffff99e96e54fa80
python3-278057 [002] 373149.138627: kfree: (fw_device_op_read+0x148) call_site=fw_device_op_read+0x148 ptr=0xffff99e8a3f06180
snd-oxfw-ctl-se-278061 [003] 373149.138636: kfree: (ioctl_send_response+0x10a) call_site=ioctl_send_response+0x10a ptr=0xffff99e96e54f4c0
python3-278055 [000] 373149.138637: kfree: (fw_device_op_read+0x148) call_site=fw_device_op_read+0x148 ptr=0xffff99e8a3f06600
python3-278055 [000] 373149.138642: kfree: (ioctl_send_response+0x10a) call_site=ioctl_send_response+0x10a ptr=0xffff99e96e54f380
python3-278057 [002] 373149.138654: kfree: (fw_request_put+0x2c) call_site=fw_request_put+0x2c ptr=0xffff99e93f007300
python3-278057 [002] 373149.138654: kfree: (ioctl_send_response+0x10a) call_site=ioctl_send_response+0x10a ptr=0xffff99e96e54f7c0

There are five listeners of IEC 61883-1 FCP region:

* Python 3: PID 278050
* Python 3: PID 278053
* Python 3: PID 278055
* Python 3: PID 278057
* snd-oxfw-ctl-service: PID 278061

When handling 1394 OHCI Asynchronous Receive context (for request) in
softIRQ context, an object is allocated for the request
(ptr=0xffff99e93f007300). When queueing event per client, the reference
count of object is increased.

The object is released when the last listener (PID 278057) executes
ioctl(2) with FW_CDEV_IOC_SEND_REQUEST request to decrease the reference
count and release event resource.

Between the event queueing and event dispatching, the core function send
response to complete transaction. The object is not released in the timing,
expectedly.

This is another log in the case to handle request to non-FCP region:

irq/35-firewire-273881 [002] 377484.348477: kmalloc: (fw_core_handle_request+0x7b) call_site=fw_core_handle_request+0x7b ptr=0xffff99e96140cd80 bytes_req=148 bytes_alloc=192 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 377484.348478: kmalloc: (handle_request+0xa8) call_site=handle_request+0xa8 ptr=0xffff99e9669303c0 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_ATOMIC
irq/35-firewire-273881 [002] 377484.348479: kmalloc: (handle_request+0xc4) call_site=handle_request+0xc4 ptr=0xffff99e99eaed0c0 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_ATOMIC
python3-280425 [001] 377484.348494: kfree: (fw_device_op_read+0x148) call_site=fw_device_op_read+0x148 ptr=0xffff99e99eaed0c0
python3-280425 [001] 377484.348563: kfree: (ioctl_send_response+0x10a) call_site=ioctl_send_response+0x10a ptr=0xffff99e9669303c0
irq/35-firewire-273881 [002] 377484.348603: kfree: (free_response_callback+0x5a) call_site=free_response_callback+0x5a ptr=0xffff99e96140cd80

The object is allocated (ptr=0xffff99e96140cd80) in the softIRQ, then
event is queued. Python 3 process (PID 280425) dispatches the event, then
execute ioctl(2) to send response. In softIRQ for 1394 OHCI Asynchronous
Receive context (for response), the object is finally released as a result
to decrease the reference count.

The reference count looks to prevent memory leak.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firewire/core-cdev.c?h=v6.1#n691
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=281e20323ab72180137824a298ee9e21e6f9acf6
[3] https://lore.kernel.org/lkml/20230117090610.93792-1-o-takashi@xxxxxxxxxxxxx/
[4] I should have elaborated the patch title...
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b2405aa948b95afc5246fa56fc05c3512cd6185c

Takashi Sakamoto (3):
firewire: core: use kref structure to maintain lifetime of data for
fw_request structure
firewire: cdev: obsolete NULL check to detect IEC 61883-1 FCP region
firewire: cdev: use single object to dispatch event for request to IEC
61883-1 FCP region

drivers/firewire/core-cdev.c | 43 +++++++++--------------
drivers/firewire/core-transaction.c | 53 +++++++++++++++++++++--------
drivers/firewire/core.h | 9 +++++
include/linux/firewire.h | 5 ++-
4 files changed, 67 insertions(+), 43 deletions(-)

--
2.37.2

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