linux-kernel - Re: hwmon: (pmbus) Add support for reading direct mode coefficients

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Date:   Thu, 10 Jun 2021 10:14:43 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Colin Ian King <colin.king@...onical.com>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        Erik Rosen <erik.rosen@...ormote.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: hwmon: (pmbus) Add support for reading direct mode coefficients

Eric,

On Thu, Jun 10, 2021 at 05:55:40PM +0100, Colin Ian King wrote:
> Hi,
> 
> Static analysis with Coverity on linux-next has detected a potential
> issue in drivers/hwmon/pmbus/pmbus_core.c with the following commit:
> 
No need to send a patch - I fixed it up by pre-initializing ret.

Thanks,
Guenter

> commit 999d577d7c007d38ab83eee4532d107c2233f78f
> Author: Erik Rosen <erik.rosen@...ormote.com>
> Date:   Wed Jun 9 11:32:06 2021 +0200
> 
>     hwmon: (pmbus) Add support for reading direct mode coefficients
> 
> The analysis is as follows:
> 
> 2219 static int pmbus_init_coefficients(struct i2c_client *client,
> 2220                                   struct pmbus_driver_info *info)
> 2221 {
> 
>     1. var_decl: Declaring variable ret without initializer.
> 
> 2222        int i, n, ret;
> 2223        const struct pmbus_class_attr_map *map;
> 2224        const struct pmbus_sensor_attr *attr;
> 2225
> 
>     2. Condition i < 6UL /* sizeof (class_attr_map) / sizeof
> (class_attr_map[0]) + (int)sizeof (struct
> pmbus_init_coefficients::[unnamed type]) */, taking true branch.
> 
>     5. Condition i < 6UL /* sizeof (class_attr_map) / sizeof
> (class_attr_map[0]) + (int)sizeof (struct
> pmbus_init_coefficients::[unnamed type]) */, taking true branch.
> 
>     8. Condition i < 6UL /* sizeof (class_attr_map) / sizeof
> (class_attr_map[0]) + (int)sizeof (struct
> pmbus_init_coefficients::[unnamed type]) */, taking true branch.
> 
> 2226        for (i = 0; i < ARRAY_SIZE(class_attr_map); i++) {
> 2227                map = &class_attr_map[i];
> 
>     3. Condition info->format[map->class] != direct, taking true branch.
>     6. Condition info->format[map->class] != direct, taking true branch.
>     9. Condition info->format[map->class] != direct, taking false branch.
> 
> 2228                if (info->format[map->class] != direct)
> 
>     4. Continuing loop.
>     7. Continuing loop.
> 
> 2229                        continue;
> 
>     10. Condition n < map->nattr, taking true branch.
>     13. Condition n < map->nattr, taking true branch.
>     16. Condition n < map->nattr, taking false branch.
> 
> 2230                for (n = 0; n < map->nattr; n++) {
> 2231                        attr = &map->attr[n];
> 
>     11. Condition map->class != attr->class, taking true branch.
>     14. Condition map->class != attr->class, taking true branch.
> 2232                        if (map->class != attr->class)
>     12. Continuing loop.
>     15. Continuing loop.
> 
> 2233                                continue;
> 2234                        ret = pmbus_read_coefficients(client, info,
> attr);
> 2235                        if (ret >= 0)
> 2236                                break;
> 2237                }
> 
> Uninitialized scalar variable (UNINIT)
>     17. uninit_use: Using uninitialized value ret.
> 
> 2238                if (ret < 0) {
> 2239                        dev_err(&client->dev,
> 2240                                "No coefficients found for sensor
> class %d\n",
> 2241                                map->class);
> 2242                        return -EINVAL;
> 2243                }
> 2244        }
> 2245
> 2246        return 0;
> 2247 }
> 
> With the continue statements on line 2233 (or if map->nattr is zero) it
> may be possible that ret is never assigned a value and so the check on
> line 2238 could be checking an uninitialized variable ret. I'm not sure
> if this is a false positive, but it may be worth initializing ret to
> some sane value to catch these corner cases.
> 
> Colin
>