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Subject[PATCH][ACPI] Let's not gamble that a possible double free will never happen in asus_hotk_get_info()
Date
Hi,

The Coverity checker points out (CID: 1500) that we can in some
cases end up doing a double free of 'model' in asus_hotk_get_info().
I'm not 100% sure it is right, but better safe than sorry,
especially since this is so simple to turn into a non-issue - simply
set 'model' to NULL after the first kfree() and then the second
kfree() is harmless (if it actually can happen, and if it cannot
happen then the cost is just a single extra assignment).

Here is the function with Coverity's annotations
(proposed patch at the end of the mail)

...
1141 /*
1142 * This function is used to initialize the hotk with right values. In this
1143 * method, we can make all the detection we want, and modify the hotk struct
1144 */
1145 static int asus_hotk_get_info(void)
1146 {
1147 struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
1148 union acpi_object *model = NULL;
1149 int bsts_result;
1150 char *string = NULL;
1151 acpi_status status;
1152
1153 /*
1154 * Get DSDT headers early enough to allow for differentiating between
1155 * models, but late enough to allow acpi_bus_register_driver() to fail
1156 * before doing anything ACPI-specific. Should we encounter a machine,
1157 * which needs special handling (i.e. its hotkey device has a different
1158 * HID), this bit will be moved. A global variable asus_info contains
1159 * the DSDT header.
1160 */
1161 status = acpi_get_table(ACPI_SIG_DSDT, 1, &asus_info);
1162 if (ACPI_FAILURE(status))
1163 printk(KERN_WARNING " Couldn't get the DSDT table header\n");
1164
1165 /* We have to write 0 on init this far for all ASUS models */
1166 if (!write_acpi_int(hotk->handle, "INIT", 0, &buffer)) {
1167 printk(KERN_ERR " Hotkey initialization failed\n");
1168 return -ENODEV;
1169 }
1170
1171 /* This needs to be called for some laptops to init properly */
1172 if (!read_acpi_int(hotk->handle, "BSTS", &bsts_result))
1173 printk(KERN_WARNING " Error calling BSTS\n");
1174 else if (bsts_result)
1175 printk(KERN_NOTICE " BSTS called, 0x%02x returned\n",
1176 bsts_result);
1177
1178 /*
1179 * Try to match the object returned by INIT to the specific model.
1180 * Handle every possible object (or the lack of thereof) the DSDT
1181 * writers might throw at us. When in trouble, we pass NULL to
1182 * asus_model_match() and try something completely different.
1183 */
1184 if (buffer.pointer) {

Event alias: aliasing "(buffer).pointer" with "model"
Also see events: [freed_arg][double_free]

1185 model = buffer.pointer;
1186 switch (model->type) {
1187 case ACPI_TYPE_STRING:
1188 string = model->string.pointer;
1189 break;
1190 case ACPI_TYPE_BUFFER:
1191 string = model->buffer.pointer;
1192 break;

At conditional (1): "default" taking true path

1193 default:

Event freed_arg: Pointer "model" freed by function "kfree"
Also see events: [alias][double_free]

1194 kfree(model);
1195 break;
1196 }
1197 }
1198 hotk->model = asus_model_match(string);

At conditional (2): "(hotk)->model == 23" taking false path

1199 if (hotk->model == END_MODEL) { /* match failed */
1200 if (asus_info &&
1201 strncmp(asus_info->oem_table_id, "ODEM", 4) == 0) {
1202 hotk->model = P30;
1203 printk(KERN_NOTICE
1204 " Samsung P30 detected, supported\n");
1205 } else {
1206 hotk->model = M2E;
1207 printk(KERN_NOTICE " unsupported model %s, trying "
1208 "default values\n", string);
1209 printk(KERN_NOTICE
1210 " send /proc/acpi/dsdt to the developers\n");
1211 }
1212 hotk->methods = &model_conf[hotk->model];
1213 return AE_OK;
1214 }
1215 hotk->methods = &model_conf[hotk->model];
1216 printk(KERN_NOTICE " %s model detected, supported\n", string);
1217
1218 /* Sort of per-model blacklist */

At conditional (3): "strncmp == 0" taking false path

1219 if (strncmp(string, "L2B", 3) == 0)
1220 hotk->methods->lcd_status = NULL;
1221 /* L2B is similar enough to L3C to use its settings, with this only
1222 exception */

At conditional (4): "strncmp == 0" taking false path

1223 else if (strncmp(string, "A3G", 3) == 0)
1224 hotk->methods->lcd_status = "\\BLFG";
1225 /* A3G is like M6R */

At conditional (5): "strncmp == 0" taking false path
At conditional (6): "strncmp == 0" taking false path
At conditional (7): "strncmp == 0" taking false path

1226 else if (strncmp(string, "S5N", 3) == 0 ||
1227 strncmp(string, "M5N", 3) == 0 ||
1228 strncmp(string, "W3N", 3) == 0)
1229 hotk->methods->mt_mled = NULL;
1230 /* S5N, M5N and W3N have no MLED */

At conditional (8): "strncmp == 0" taking false path

1231 else if (strncmp(string, "L5D", 3) == 0)
1232 hotk->methods->mt_wled = NULL;
1233 /* L5D's WLED is not controlled by ACPI */

At conditional (9): "strncmp == 0" taking false path
At conditional (10): "strncmp == 0" taking false path
At conditional (11): "strncmp == 0" taking false path

1234 else if (strncmp(string, "M2N", 3) == 0 ||
1235 strncmp(string, "W3V", 3) == 0 ||
1236 strncmp(string, "S1N", 3) == 0)
1237 hotk->methods->mt_wled = "WLED";
1238 /* M2N, S1N and W3V have a usable WLED */

At conditional (12): "asus_info != 0" taking true path

1239 else if (asus_info) {

At conditional (13): "strncmp == 0" taking false path

1240 if (strncmp(asus_info->oem_table_id, "L1", 2) == 0)
1241 hotk->methods->mled_status = NULL;
1242 /* S1300A reports L84F, but L1400B too, account for that */
1243 }
1244

Event double_free: Double free of pointer "model" in call to "kfree"
Also see events: [alias][freed_arg]

1245 kfree(model);
1246
1247 return AE_OK;
1248 }
...




Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
---

drivers/acpi/asus_acpi.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/asus_acpi.c b/drivers/acpi/asus_acpi.c
index 9c4bd22..86fd142 100644
--- a/drivers/acpi/asus_acpi.c
+++ b/drivers/acpi/asus_acpi.c
@@ -1192,6 +1192,7 @@ static int asus_hotk_get_info(void)
break;
default:
kfree(model);
+ model = NULL;
break;
}
}



Please Cc me on replies...


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