[PATCH] hwmon: (gpio-fan) Fix array out of bounds access

[Armin Wolf]

When set_fan_speed() is called with speed_index being
greater than num_speed or less than 0, an array out of bounds
access occurs. This can be exploited by setting the state of
the thermal cooling device to arbitrary values, causing for example
a kernel oops when unavailable memory is accessed this way.

Example kernel oops:
[  807.987276] Unable to handle kernel paging request at virtual address ffffff80d0588064
[  807.987369] Mem abort info:
[  807.987398]   ESR = 0x96000005
[  807.987428]   EC = 0x25: DABT (current EL), IL = 32 bits
[  807.987477]   SET = 0, FnV = 0
[  807.987507]   EA = 0, S1PTW = 0
[  807.987536]   FSC = 0x05: level 1 translation fault
[  807.987570] Data abort info:
[  807.987763]   ISV = 0, ISS = 0x00000005
[  807.987801]   CM = 0, WnR = 0
[  807.987832] swapper pgtable: 4k pages, 39-bit VAs, pgdp=0000000001165000
[  807.987872] [ffffff80d0588064] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000
[  807.987961] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[  807.987992] Modules linked in: cmac algif_hash aes_arm64 algif_skcipher af_alg bnep hci_uart btbcm bluetooth ecdh_generic ecc 8021q garp stp llc snd_soc_hdmi_codec brcmfmac vc4 brcmutil cec drm_kms_helper snd_soc_core cfg80211 snd_compress bcm2835_codec(C) snd_pcm_dmaengine syscopyarea bcm2835_isp(C) bcm2835_v4l2(C) sysfillrect v4l2_mem2mem bcm2835_mmal_vchiq(C) raspberrypi_hwmon sysimgblt videobuf2_dma_contig videobuf2_vmalloc fb_sys_fops videobuf2_memops rfkill videobuf2_v4l2 videobuf2_common i2c_bcm2835 snd_bcm2835(C) videodev snd_pcm snd_timer snd mc vc_sm_cma(C) gpio_fan uio_pdrv_genirq uio drm fuse drm_panel_orientation_quirks backlight ip_tables x_tables ipv6
[  807.988508] CPU: 0 PID: 1321 Comm: bash Tainted: G         C        5.15.56-v8+ #1575
[  807.988548] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
[  807.988574] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[  807.988608] pc : set_fan_speed.part.5+0x34/0x80 [gpio_fan]
[  807.988654] lr : gpio_fan_set_cur_state+0x34/0x50 [gpio_fan]
[  807.988691] sp : ffffffc008cf3bd0
[  807.988710] x29: ffffffc008cf3bd0 x28: ffffff80019edac0 x27: 0000000000000000
[  807.988762] x26: 0000000000000000 x25: 0000000000000000 x24: ffffff800747c920
[  807.988787] x23: 000000000000000a x22: ffffff800369f000 x21: 000000001999997c
[  807.988854] x20: ffffff800369f2e8 x19: ffffff8002ae8080 x18: 0000000000000000
[  807.988877] x17: 0000000000000000 x16: 0000000000000000 x15: 000000559e271b70
[  807.988938] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
[  807.988960] x11: 0000000000000000 x10: ffffffc008cf3c20 x9 : ffffffcfb60c741c
[  807.989018] x8 : 000000000000000a x7 : 00000000ffffffc9 x6 : 0000000000000009
[  807.989040] x5 : 000000000000002a x4 : 0000000000000000 x3 : ffffff800369f2e8
[  807.989062] x2 : 000000000000e780 x1 : 0000000000000001 x0 : ffffff80d0588060
[  807.989084] Call trace:
[  807.989091]  set_fan_speed.part.5+0x34/0x80 [gpio_fan]
[  807.989113]  gpio_fan_set_cur_state+0x34/0x50 [gpio_fan]
[  807.989199]  cur_state_store+0x84/0xd0
[  807.989221]  dev_attr_store+0x20/0x38
[  807.989262]  sysfs_kf_write+0x4c/0x60
[  807.989282]  kernfs_fop_write_iter+0x130/0x1c0
[  807.989298]  new_sync_write+0x10c/0x190
[  807.989315]  vfs_write+0x254/0x378
[  807.989362]  ksys_write+0x70/0xf8
[  807.989379]  __arm64_sys_write+0x24/0x30
[  807.989424]  invoke_syscall+0x4c/0x110
[  807.989442]  el0_svc_common.constprop.3+0xfc/0x120
[  807.989458]  do_el0_svc+0x2c/0x90
[  807.989473]  el0_svc+0x24/0x60
[  807.989544]  el0t_64_sync_handler+0x90/0xb8
[  807.989558]  el0t_64_sync+0x1a0/0x1a4
[  807.989579] Code: b9403801 f9402800 7100003f 8b35cc00 (b9400416)
[  807.989627] ---[ end trace 8ded4c918658445b ]---

Fix this by checking speed_index and return if it is out of bounds.

Tested on a Raspberry Pi 3.

Fixes: d6fe1360f42e ("hwmon: add generic GPIO fan driver")
Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
---
 drivers/hwmon/gpio-fan.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index befe989ca7b9..1d6facee44e0 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -128,6 +128,9 @@ static int __get_fan_ctrl(struct gpio_fan_data *fan_data)
 /* Must be called with fan_data->lock held, except during initialization. */
 static void set_fan_speed(struct gpio_fan_data *fan_data, int speed_index)
 {
+	if (speed_index >= fan_data->num_speed || speed_index < 0)
+		return;
+
 	if (fan_data->speed_index == speed_index)
 		return;

--
2.30.2