[PATCH] i2c: core: fix NULL pointer dereference in suspend/resume callbacks

[Marek Szyprowski <m.szyprowski@samsung.com>]

Commit 6fe12cdbcfe3 ("i2c: core: support bus regulator controlling in
adapter") added generic suspend and resume functions for i2c devices.
Those functions unconditionally access an i2c_client structure assigned
to the given i2c device. However, there exist i2c devices in the system
without a valid i2c_client. Add the needed check before accessing the
i2c_client.

This fixes the following issue observed on Samsung Exynos4412-based
Odroid U3 board:

8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000018
pgd = 2aed198a
[00000018] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 1 PID: 1295 Comm: rtcwake Not tainted 5.7.0-rc6-02700-g4773d1324da6 #739
Hardware name: Samsung Exynos (Flattened Device Tree)
PC is at i2c_suspend_late+0x20/0x48
LR is at dpm_run_callback+0xb4/0x3fc
pc : [<c07b404c>]    lr : [<c064b7cc>]    psr: 20000053
...
Process rtcwake (pid: 1295, stack limit = 0x7f1885cf)
Stack: (0xec8f3d70 to 0xec8f4000)
...
[<c07b404c>] (i2c_suspend_late) from [<c064b7cc>] (dpm_run_callback+0xb4/0x3fc)
[<c064b7cc>] (dpm_run_callback) from [<c064ce04>] (__device_suspend_late+0xcc/0x16c)
[<c064ce04>] (__device_suspend_late) from [<c064f0b0>] (dpm_suspend_late+0x10c/0x568)
[<c064f0b0>] (dpm_suspend_late) from [<c01996f0>] (suspend_devices_and_enter+0x31c/0xc70)
[<c01996f0>] (suspend_devices_and_enter) from [<c019a43c>] (pm_suspend+0x3f8/0x480)
[<c019a43c>] (pm_suspend) from [<c0198174>] (state_store+0x6c/0xc8)
[<c0198174>] (state_store) from [<c035cf4c>] (kernfs_fop_write+0x10c/0x228)
[<c035cf4c>] (kernfs_fop_write) from [<c02b94a4>] (__vfs_write+0x30/0x1d0)
[<c02b94a4>] (__vfs_write) from [<c02bc444>] (vfs_write+0xa4/0x170)
[<c02bc444>] (vfs_write) from [<c02bc690>] (ksys_write+0x60/0xd8)
[<c02bc690>] (ksys_write) from [<c0100060>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xec8f3fa8 to 0xec8f3ff0)
...
---[ end trace a43afef431782f37 ]---

Fixes: 6fe12cdbcfe3 ("i2c: core: support bus regulator controlling in adapter")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
This fixes suspend/resume issue observed on various board with linux-next
from 20200521.
---
 drivers/i2c/i2c-core-base.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 5be24bf8a194..b531f5ad06b2 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -454,11 +454,13 @@ static int i2c_device_remove(struct device *dev)
 static int i2c_resume_early(struct device *dev)
 {
 	struct i2c_client *client = i2c_verify_client(dev);
-	struct i2c_adapter *adap = client->adapter;
 	int err;
 
+	if (!client)
+		return 0;
+
 	if (!pm_runtime_status_suspended(&client->dev)) {
-		err = regulator_enable(adap->bus_regulator);
+		err = regulator_enable(client->adapter->bus_regulator);
 		if (err)
 			return err;
 	}
@@ -469,15 +471,17 @@ static int i2c_resume_early(struct device *dev)
 static int i2c_suspend_late(struct device *dev)
 {
 	struct i2c_client *client = i2c_verify_client(dev);
-	struct i2c_adapter *adap = client->adapter;
 	int err;
 
+	if (!client)
+		return 0;
+
 	err = pm_generic_suspend_late(&client->dev);
 	if (err)
 		return err;
 
 	if (!pm_runtime_status_suspended(&client->dev))
-		return regulator_disable(adap->bus_regulator);
+		return regulator_disable(client->adapter->bus_regulator);
 
 	return 0;
 }
@@ -487,10 +491,12 @@ static int i2c_suspend_late(struct device *dev)
 static int i2c_runtime_resume(struct device *dev)
 {
 	struct i2c_client *client = i2c_verify_client(dev);
-	struct i2c_adapter *adap = client->adapter;
 	int err;
 
-	err = regulator_enable(adap->bus_regulator);
+	if (!client)
+		return 0;
+
+	err = regulator_enable(client->adapter->bus_regulator);
 	if (err)
 		return err;
 
@@ -500,14 +506,16 @@ static int i2c_runtime_resume(struct device *dev)
 static int i2c_runtime_suspend(struct device *dev)
 {
 	struct i2c_client *client = i2c_verify_client(dev);
-	struct i2c_adapter *adap = client->adapter;
 	int err;
 
+	if (!client)
+		return 0;
+
 	err = pm_generic_runtime_suspend(&client->dev);
 	if (err)
 		return err;
 
-	return regulator_disable(adap->bus_regulator);
+	return regulator_disable(client->adapter->bus_regulator);
 }
 #endif
 
-- 
2.17.1