On Thu, 20 May 2021 10:58:21 +0200, Colin Ian King wrote:

Hi,

Static analysis with Coverity on linux-next has detected an uninitialized variable issue with the following commit:

commit 481f17c41803985446fd12887b2c042f9c43b0d5 Author: Takashi Iwai tiwai@suse.de Date: Tue May 18 17:21:12 2021 +0200

ALSA: usb-audio: Handle error for the current selector gracefully

The branching is a bit convoluted and we end up with variable cur not being initialized. Analysis is as follows:

254static int __uac_clock_find_source(struct snd_usb_audio *chip, 255 const struct audioformat *fmt, int entity_id, 256 unsigned long *visited, bool validate) 257{ 258 union uac23_clock_source_desc *source; 259 union uac23_clock_selector_desc *selector; 260 union uac23_clock_multiplier_desc *multiplier;

1. var_decl: Declaring variable cur without initializer.

261 int ret, i, cur, err, pins, clock_id; 262 const u8 *sources; 263 int proto = fmt->protocol; 264 265 entity_id &= 0xff; 266

2. Condition test_and_set_bit(entity_id, visited), taking false

branch.

267 if (test_and_set_bit(entity_id, visited)) { 268 usb_audio_warn(chip, 269 "%s(): recursive clock topology detected, id %d.\n", 270 __func__, entity_id); 271 return -EINVAL; 272 } 273 274 /* first, see if the ID we're looking for is a clock source already */ 275 source = snd_usb_find_clock_source(chip, entity_id, proto);

3. Condition source, taking false branch.

276 if (source) { 277 entity_id = GET_VAL(source, proto, bClockID); 278 if (validate && !uac_clock_source_is_valid(chip, fmt, 279 entity_id)) { 280 usb_audio_err(chip, 281 "clock source %d is not valid, cannot use\n", 282 entity_id); 283 return -ENXIO; 284 } 285 return entity_id; 286 } 287 288 selector = snd_usb_find_clock_selector(chip, entity_id, proto);

4. Condition selector, taking true branch.

289 if (selector) { 5. Condition proto == 48, taking true branch. 290 pins = GET_VAL(selector, proto, bNrInPins); 6. Condition proto == 48, taking true branch. 291 clock_id = GET_VAL(selector, proto, bClockID); 7. Condition proto == 48, taking true branch. 292 sources = GET_VAL(selector, proto, baCSourceID); 293 8. Condition pins == 1, taking false branch.

294 if (pins == 1) { 295 ret = 1; 296 goto find_source; 297 } 298 299 /* the entity ID we are looking for is a selector. 300 * find out what it currently selects */ 301 ret = uac_clock_selector_get_val(chip, clock_id);

9. Condition ret < 0, taking true branch.

302 if (ret < 0) {

10. Condition !chip->autoclock, taking false branch.

303 if (!chip->autoclock) 304 return ret;

11. Jumping to label find_others.

305 goto find_others; 306 } 307 308 /* Selector values are one-based */ 309 310 if (ret > pins || ret < 1) { 311 usb_audio_err(chip, 312 "%s(): selector reported illegal value, id %d, ret %d\n", 313 __func__, clock_id, ret); 314 315 if (!chip->autoclock) 316 return -EINVAL; 317 ret = 0; 318 goto find_others; 319 } 320 321 find_source: 322 cur = ret; 323 ret = __uac_clock_find_source(chip, fmt, 324 sources[ret - 1], 325 visited, validate); 326 if (ret > 0) { 327 err = uac_clock_selector_set_val(chip, entity_id, cur); 328 if (err < 0) 329 return err; 330 } 331 332 if (!validate || ret > 0 || !chip->autoclock) 333 return ret; 334 335 find_others: 336 /* The current clock source is invalid, try others. */ 12. Condition i <= pins, taking true branch. 337 for (i = 1; i <= pins; i++) {

Uninitialized scalar variable (UNINIT)

13. uninit_use: Using uninitialized value cur.

338 if (i == cur) 339 continue; 340

Thanks, it looks indeed like a possible scenario. The fix patch is below.

Takashi

-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: usb-audio: Fix uninitialized variable at __uac_clock_find_source()

The cur variable indicating the currently selected clock source can be theoretically used as uninitialized after the recent commit 481f17c41803 ("ALSA: usb-audio: Handle error for the current selector gracefully"). For addressing it, initialize it before use.

Also, one place seems setting 0 to a wrong variable ret, instead of cur; otherwise it makes little sense. Since the initialization is done beforehand, we can get rid of this line, too.

Fixes: 481f17c41803 ("ALSA: usb-audio: Handle error for the current selector gracefully") Reported-by: Colin Ian King colin.king@canonical.com Link: https://lore.kernel.org/r/4b261d68-f53f-240d-2d8a-2f88b337849d@canonical.com Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/usb/clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/clock.c b/sound/usb/clock.c index 772478c725c2..0afae839d295 100644 --- a/sound/usb/clock.c +++ b/sound/usb/clock.c @@ -290,6 +290,7 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip, pins = GET_VAL(selector, proto, bNrInPins); clock_id = GET_VAL(selector, proto, bClockID); sources = GET_VAL(selector, proto, baCSourceID); + cur = 0;

if (pins == 1) { ret = 1; @@ -314,7 +315,6 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip,

if (!chip->autoclock) return -EINVAL; - ret = 0; goto find_others; }