Re: [PATCH] firmware: fix NULL pointer dereference in __fw_load_abort()

[Luis R. Rodriguez]

On Wed, Jan 04, 2017 at 06:19:40PM +0100, linux-kernel-dev@xxxxxxxxxxxx wrote:
> From: Patrick Bruenn <p.bruenn@xxxxxxxxxxxx>
> 
> Since commit 5d47ec02c37ea632398cb251c884e3a488dff794
> ("firmware: Correct handling of fw_state_wait() return value")
> 
> I see the following NULL pointer dereference:
> [    0.000000] Booting Linux on physical CPU 0x0
> [    0.000000] Linux version 4.10.0-rc2-CX9020-10+ (patrickbr@lbs1) (gcc version 5.4.0 20160609 (Debian 5.4.0-6) ) #23 PREEMPT Wed Jan 4 08:10:24 CET 2017
> [    0.000000] CPU: ARMv7 Processor [412fc085] revision 5 (ARMv7), cr=10c5387d
> [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
> [    0.000000] OF: fdt:Machine model: Freescale i.MX53 based Beckhoff CX9020
> ...
> [    3.098826] Unable to handle kernel NULL pointer dereference at virtual address 00000018
> [    3.115823] pgd = c0004000
> [    3.118632] [00000018] *pgd=00000000
> [    3.122279] Internal error: Oops: 17 [#1] PREEMPT ARM
> [    3.127406] Modules linked in: pwm_imx parallel_display panel_simple uio_pdrv_genirq uio
> [    3.135637] CPU: 0 PID: 26 Comm: kworker/0:1 Not tainted 4.10.0-rc2-CX9020-10+ #23
> [    3.143313] Hardware name: Freescale i.MX53 (Device Tree Support)
> [    3.149517] Workqueue: events request_firmware_work_func
> [    3.154908] task: dedbde00 task.stack: dee76000
> [    3.159510] PC is at _request_firmware+0x878/0x948
> [    3.164375] LR is at __mutex_lock_slowpath+0x2a8/0x340
> [    3.169576] pc : [<c04ffd80>]    lr : [<c073f5e8>]    psr: 60030013
> sp : dee77e68  ip : dee77e20  fp : dee77ed4
> [    3.181183] r10: dee56a08  r9 : ded92410  r8 : dee56a00
> [    3.186470] r7 : dee77ee4  r6 : fffffffe  r5 : def41680  r4 : deeb1e00
> [    3.193070] r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : 00000000
> [    3.199673] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
> [    3.206891] Control: 10c5387d  Table: 8e1c8019  DAC: 00000051
> [    3.212704] Process kworker/0:1 (pid: 26, stack limit = 0xdee76210)
> [    3.219044] Stack: (0xdee77e68 to 0xdee78000)
> [    3.223458] 7e60:                   7fffffff 00000000 00000001 c0102e2c c0c7a088 c0c735f8
> [    3.231731] 7e80: c0c5124c 00000002 00000001 7fffffff c0c04384 c0d1ae30 00001770 dec9d000
> [    3.240004] 7ea0: dedbde00 c0c12708 00000000 def41580 dee55680 c0c0ff68 df263100 00000000
> [    3.248290] 7ec0: 00000000 c0c6daf8 dee77efc dee77ed8 c04fffbc c04ff514 00000000 00000007
> [    3.256565] 7ee0: 0c0e0832 c01413dc def41580 def41580 dee77f34 dee77f00 c0141420 c04fff8c
> [    3.264841] 7f00: c0c0ff7c dee76038 dee58558 c0c0ff68 dee55698 c0c17e00 c0c0ff7c dee76038
> [    3.273115] 7f20: 00000008 dee55680 dee77f7c dee77f38 c014186c c01412f0 dee77f54 dee76000
> [    3.281387] 7f40: 00000000 dee53cc0 c0c17e00 c0c217a1 dee58558 dee58540 00000000 dee53cc0
> [    3.289667] 7f60: dee55680 c0141810 dee58558 ded0be94 dee77fac dee77f80 c0147dfc c014181c
> [    3.297945] 7f80: dee76000 dee53cc0 c0147ce8 00000000 00000000 00000000 00000000 00000000
> [    3.306217] 7fa0: 00000000 dee77fb0 c0108e18 c0147cf4 00000000 00000000 00000000 00000000
> [    3.314489] 7fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [    3.322762] 7fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ffffffff ffffffff
> [    3.331055] [<c04ffd80>] (_request_firmware) from [<c04fffbc>] (request_firmware_work_func+0x3c/0x74)
> [    3.343535] [<c04fffbc>] (request_firmware_work_func) from [<c0141420>] (process_one_work+0x13c/0x52c)
> [    3.356057] [<c0141420>] (process_one_work) from [<c014186c>] (worker_thread+0x5c/0x620)
> [    3.367393] [<c014186c>] (worker_thread) from [<c0147dfc>] (kthread+0x114/0x144)
> [    3.378045] [<c0147dfc>] (kthread) from [<c0108e18>] (ret_from_fork+0x14/0x3c)
> [    3.388481] Code: eafffdf5 e59f00bc eb08fe40 e5980100 (e5903018)
> [    3.682255] ---[ end trace dbbc5ea21820dd99 ]---
> 
> I believe I tracked it down to:
> drivers/dma/imx-sdma.c request_firmware()
> -> fw_load_from_user_helper()
> -> _request_firmware_load()
> -> call fw_state_wait_timeout()
> 
> Some time later firmware_loading_store() scans a control value of "-1"
> -> switch(loading) case -1: will call
> -> fw_load_abort(fw_priv) which calls
> -> __fw_load_abort(fw_priv->buf)
> -> and set fw_priv->buf = NULL;
> 
> back in _request_firmware_load()
> fw_state_wait_timeout() returns -ENOENT
> -> since mentioned commit
> -> fw_load_abort(fw_priv) is called a second time
> -> and this time it would call:
> -> __fw_load_abort(NULL /* fw_priv->buf */)
> -> and we get: NULL->fw_st.status which fits 0x18:
> offsetof(struct firmware_buf, fw_st) + offsetof(struct fw_state, status)
> 
> As a novice, I have no idea how to fix the original patch in a clean way.
> My workaround is to just check buf in fw_load_abort() or __fw_load_abort()
> Maybe I am totally wrong and misconfigured my board.
> Feedback is very much appreciated.
> 
> Signed-off-by: Patrick Bruenn <p.bruenn@xxxxxxxxxxxx>
> ---
>  drivers/base/firmware_class.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index 4497d263209f..3960ee117453 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -542,6 +542,8 @@ static struct firmware_priv *to_firmware_priv(struct device *dev)
>  
>  static void __fw_load_abort(struct firmware_buf *buf)
>  {
> +	if (!buf)
> +		return;
>  	/*
>  	 * There is a small window in which user can write to 'loading'
>  	 * between loading done and disappearance of 'loading'

Chris beat you to it earlier today but his patch is on fw_load_abort() not on
__fw_load_abort(), upon closer inspection since  we can call the later in
another place its best as in your patch. Chris can you use Patrick's oops,
shift your fix as his, and use also Fixes:
5d47ec02c37ea632398cb251c884e3a488dff794 ("firmware: Correct handling of
fw_state_wait() return value") as well as a Stable tag.

  Luis