Re: [PATCH v2] gpiolib-acpi: Duplicate con_id string when adding it to the crs lookup list

[Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>]

On Thu, Apr 28, 2016 at 08:55:36PM +0900, Alexandre Courbot wrote:
> On Thu, Apr 28, 2016 at 7:33 PM, Ville Syrjälä
> <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> > On Thu, Apr 28, 2016 at 02:04:10PM +0900, Alexandre Courbot wrote:
> >> On Mon, Apr 25, 2016 at 10:01 PM,  <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> >> > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >> >
> >> > Calling gpiod_get() from a module and then unloading the module leads to an
> >> > oops due to acpi_can_fallback_to_crs() storing the pointer to the passed
> >> > 'con_id' string onto acpi_crs_lookup_list. The next guy to come along will then
> >> > try to access the string but the memory may now be gone with the module.
> >> > Make a copy of the passed string instead, and store the copy on the list.
> >> >
> >> > BUG: unable to handle kernel paging request at ffffffffa03e7855
> >> > IP: [<ffffffff81338322>] strcmp+0x12/0x30
> >> > PGD 2a07067 PUD 2a08063 PMD 74720067 PTE 0
> >> > Oops: 0000 [#1] PREEMPT SMP
> >> > Modules linked in: i915(+) drm_kms_helper drm intel_gtt snd_hda_codec snd_hda_core i2c_algo_bit syscopya
> >> > rea sysfillrect sysimgblt fb_sys_fops agpgart snd_soc_sst_bytcr_rt5640 coretemp hwmon intel_rapl intel_soc_dts_thermal
> >> > punit_atom_debug snd_soc_rt5640 snd_soc_rl6231 serio snd_intel_sst_acpi snd_intel_sst_core video snd_soc_sst_mfld_platf
> >> > orm snd_soc_sst_match backlight int3402_thermal processor_thermal_device int3403_thermal int3400_thermal acpi_thermal_r
> >> > el snd_soc_core intel_soc_dts_iosf int340x_thermal_zone snd_compress i2c_hid hid snd_pcm snd_timer snd soundcore evdev
> >> > sch_fq_codel efivarfs ipv6 autofs4 [last unloaded: drm]
> >> > CPU: 2 PID: 3064 Comm: modprobe Tainted: G     U  W       4.6.0-rc3-ffrd-ipvr+ #302
> >> > Hardware name: Intel Corp. VALLEYVIEW C0 PLATFORM/BYT-T FFD8, BIOS BLAKFF81.X64.0088.R10.1403240443 FFD8
> >> > _X64_R_2014_13_1_00 03/24/2014
> >> > task: ffff8800701cd200 ti: ffff880070034000 task.ti: ffff880070034000
> >> > RIP: 0010:[<ffffffff81338322>]  [<ffffffff81338322>] strcmp+0x12/0x30
> >> > RSP: 0000:ffff880070037748  EFLAGS: 00010286
> >> > RAX: 0000000080000000 RBX: ffff88007a342800 RCX: 0000000000000006
> >> > RDX: 0000000000000006 RSI: ffffffffa054f856 RDI: ffffffffa03e7856
> >> > RBP: ffff880070037748 R08: 0000000000000000 R09: 0000000000000001
> >> > R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffa054f855
> >> > R13: ffff88007281cae0 R14: 0000000000000010 R15: ffffffffffffffea
> >> > FS:  00007faa51447700(0000) GS:ffff880079300000(0000) knlGS:0000000000000000
> >> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> > CR2: ffffffffa03e7855 CR3: 0000000041eba000 CR4: 00000000001006e0
> >> > Stack:
> >> >  ffff880070037770 ffffffff8136ad28 ffffffffa054f855 0000000000000000
> >> >  ffff88007a0a2098 ffff8800700377e8 ffffffff8136852e ffff88007a342800
> >> >  00000007700377a0 ffff8800700377a0 ffffffff81412442 70672d6c656e6170
> >> > Call Trace:
> >> >  [<ffffffff8136ad28>] acpi_can_fallback_to_crs+0x88/0x100
> >> >  [<ffffffff8136852e>] gpiod_get_index+0x25e/0x310
> >> >  [<ffffffff81412442>] ? mipi_dsi_attach+0x22/0x30
> >> >  [<ffffffff813685f2>] gpiod_get+0x12/0x20
> >> >  [<ffffffffa04fcf41>] intel_dsi_init+0x421/0x480 [i915]
> >> >  [<ffffffffa04d3783>] intel_modeset_init+0x853/0x16b0 [i915]
> >> >  [<ffffffffa0504864>] ? intel_setup_gmbus+0x214/0x260 [i915]
> >> >  [<ffffffffa0510158>] i915_driver_load+0xdc8/0x19b0 [i915]
> >> >  [<ffffffff8160fb53>] ? _raw_spin_unlock_irqrestore+0x43/0x70
> >> >  [<ffffffffa026b13b>] drm_dev_register+0xab/0xc0 [drm]
> >> >  [<ffffffffa026d7b3>] drm_get_pci_dev+0x93/0x1f0 [drm]
> >> >  [<ffffffff8160fb53>] ? _raw_spin_unlock_irqrestore+0x43/0x70
> >> >  [<ffffffffa043f1f4>] i915_pci_probe+0x34/0x50 [i915]
> >> >  [<ffffffff81379751>] pci_device_probe+0x91/0x100
> >> >  [<ffffffff8141a75a>] driver_probe_device+0x20a/0x2d0
> >> >  [<ffffffff8141a8be>] __driver_attach+0x9e/0xb0
> >> >  [<ffffffff8141a820>] ? driver_probe_device+0x2d0/0x2d0
> >> >  [<ffffffff81418439>] bus_for_each_dev+0x69/0xa0
> >> >  [<ffffffff8141a04e>] driver_attach+0x1e/0x20
> >> >  [<ffffffff81419c20>] bus_add_driver+0x1c0/0x240
> >> >  [<ffffffff8141b6d0>] driver_register+0x60/0xe0
> >> >  [<ffffffff81377d20>] __pci_register_driver+0x60/0x70
> >> >  [<ffffffffa026d9f4>] drm_pci_init+0xe4/0x110 [drm]
> >> >  [<ffffffff810ce04e>] ? trace_hardirqs_on+0xe/0x10
> >> >  [<ffffffffa02f1000>] ? 0xffffffffa02f1000
> >> >  [<ffffffffa02f1094>] i915_init+0x94/0x9b [i915]
> >> >  [<ffffffff810003bb>] do_one_initcall+0x8b/0x1c0
> >> >  [<ffffffff810eb616>] ? rcu_read_lock_sched_held+0x86/0x90
> >> >  [<ffffffff811de6d6>] ? kmem_cache_alloc_trace+0x1f6/0x270
> >> >  [<ffffffff81183826>] do_init_module+0x60/0x1dc
> >> >  [<ffffffff81115a8d>] load_module+0x1d0d/0x2390
> >> >  [<ffffffff811120b0>] ? __symbol_put+0x70/0x70
> >> >  [<ffffffff811f41b2>] ? kernel_read_file+0x92/0x120
> >> >  [<ffffffff811162f4>] SYSC_finit_module+0xa4/0xb0
> >> >  [<ffffffff8111631e>] SyS_finit_module+0xe/0x10
> >> >  [<ffffffff81001ff3>] do_syscall_64+0x63/0x350
> >> >  [<ffffffff816103da>] entry_SYSCALL64_slow_path+0x25/0x25
> >> > Code: f7 48 8d 76 01 48 8d 52 01 0f b6 4e ff 84 c9 88 4a ff 75 ed 5d c3 0f 1f 00 55 48 89 e5 eb 04 84 c0
> >> >  74 18 48 8d 7f 01 48 8d 76 01 <0f> b6 47 ff 3a 46 ff 74 eb 19 c0 83 c8 01 5d c3 31 c0 5d c3 66
> >> > RIP  [<ffffffff81338322>] strcmp+0x12/0x30
> >> >  RSP <ffff880070037748>
> >> > CR2: ffffffffa03e7855
> >> >
> >> > v2: Make the copied con_id const
> >> >
> >> > Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> >> > Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> >> > Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> >> > Cc: Alexandre Courbot <gnurou@xxxxxxxxx>
> >> > Cc: stable@xxxxxxxxxxxxxxx
> >> > Fixes: 10cf4899f8af ("gpiolib: tighten up ACPI legacy gpio lookups")
> >> > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> >> > ---
> >> >  drivers/gpio/gpiolib-acpi.c | 2 +-
> >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >> >
> >> > diff --git a/drivers/gpio/gpiolib-acpi.c b/drivers/gpio/gpiolib-acpi.c
> >> > index 682070d20f00..2dc52585e3f2 100644
> >> > --- a/drivers/gpio/gpiolib-acpi.c
> >> > +++ b/drivers/gpio/gpiolib-acpi.c
> >> > @@ -977,7 +977,7 @@ bool acpi_can_fallback_to_crs(struct acpi_device *adev, const char *con_id)
> >> >                 lookup = kmalloc(sizeof(*lookup), GFP_KERNEL);
> >> >                 if (lookup) {
> >> >                         lookup->adev = adev;
> >> > -                       lookup->con_id = con_id;
> >> > +                       lookup->con_id = kstrdup(con_id, GFP_KERNEL);
> >>
> >> Agree with the idea, but where is this newly-allocated memory freed?
> >
> > It isn't. Neither is the 'lookup' thing itself.
> 
> Are we ok with that? Leaking memory is slightly better than crashing a
> driver, but that is still not something to be fond of...

When would you free it?

-- 
Ville Syrjälä
Intel OTC
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