gpiolib-acpi: Duplicate con_id string when adding it to the crs lookup list

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@gmail.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: stable@vger.kernel.org
Fixes: 10cf4899 ("gpiolib: tighten up ACPI legacy gpio lookups")
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>

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);
 			list_add_tail(&lookup->node, &acpi_crs_lookup_list);
 		}
 	}