Re: [PATCH 2/2] tty: add retry to tty_init_dev() to workaround a race condition

Dan Carpenter
2019-11-25T06:29:02Z

Hi Sudip,

[auto build test WARNING on v5.4-rc8]
[cannot apply to tty/tty-testing next-20191122]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url: https://github.com/0day-ci/linux/commits/Sudip-Mukherjee/tty-remove-unused-argument-from-tty_open_by_driver/20191123-164153
base: af42d3466bdc8f39806b26f593604fdc54140bcb

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

smatch warnings:
drivers/tty/tty_io.c:1360 tty_init_dev() error: we previously assumed 'tty->port' could be null (see line 1348)

# https://github.com/0day-ci/linux/commit/8de47da07f8c6fe6f631965cafb384cd0d72ce40
git remote add linux-review https://github.com/0day-ci/linux
git remote update linux-review
git checkout 8de47da07f8c6fe6f631965cafb384cd0d72ce40
vim +1360 drivers/tty/tty_io.c

8de47da07f8c6f drivers/tty/tty_io.c Sudip Mukherjee 2019-11-20 1318 struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
8de47da07f8c6f drivers/tty/tty_io.c Sudip Mukherjee 2019-11-20 1319 int retry)
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1320 {
bf970ee46e0fb3 drivers/char/tty_io.c Alan Cox 2008-10-13 1321 struct tty_struct *tty;
73ec06fc5f5c8e drivers/char/tty_io.c Alan Cox 2008-10-13 1322 int retval;
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1323
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1324 /*
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1325 * First time open is complex, especially for PTY devices.
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1326 * This code guarantees that either everything succeeds and the
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1327 * TTY is ready for operation, or else the table slots are vacated
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1328 * and the allocated memory released. (Except that the termios
16b00ae82dce0e drivers/tty/tty_io.c Johan Hovold 2017-03-30 1329 * may be retained.)
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1330 */
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1331
73ec06fc5f5c8e drivers/char/tty_io.c Alan Cox 2008-10-13 1332 if (!try_module_get(driver->owner))
73ec06fc5f5c8e drivers/char/tty_io.c Alan Cox 2008-10-13 1333 return ERR_PTR(-ENODEV);
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1334
2c964a2f4191f2 drivers/tty/tty_io.c Rasmus Villemoes 2014-07-10 1335 tty = alloc_tty_struct(driver, idx);
d5543503753983 drivers/tty/tty_io.c Jiri Slaby 2011-03-23 1336 if (!tty) {
d5543503753983 drivers/tty/tty_io.c Jiri Slaby 2011-03-23 1337 retval = -ENOMEM;
d5543503753983 drivers/tty/tty_io.c Jiri Slaby 2011-03-23 1338 goto err_module_put;
d5543503753983 drivers/tty/tty_io.c Jiri Slaby 2011-03-23 1339 }
^1da177e4c3f41 drivers/char/tty_io.c Linus Torvalds 2005-04-16 1340
89c8d91e31f267 drivers/tty/tty_io.c Alan Cox 2012-08-08 1341 tty_lock(tty);
73ec06fc5f5c8e drivers/char/tty_io.c Alan Cox 2008-10-13 1342 retval = tty_driver_install_tty(driver, tty);
d5543503753983 drivers/tty/tty_io.c Jiri Slaby 2011-03-23 1343 if (retval < 0)
c8b710b3e43481 drivers/tty/tty_io.c Peter Hurley 2016-01-09 1344 goto err_free_tty;
8b0a88d5912ab5 drivers/char/tty_io.c Alan Cox 2008-10-13 1345
04831dc154df9b drivers/tty/tty_io.c Jiri Slaby 2012-06-04 1346 if (!tty->port)
04831dc154df9b drivers/tty/tty_io.c Jiri Slaby 2012-06-04 1347 tty->port = driver->ports[idx];
8de47da07f8c6f drivers/tty/tty_io.c Sudip Mukherjee 2019-11-20 @1348 if (!tty->port && retry) {
^^^^^^^^^^
Check

8de47da07f8c6f drivers/tty/tty_io.c Sudip Mukherjee 2019-11-20 1349 retval = -EAGAIN;
8de47da07f8c6f drivers/tty/tty_io.c Sudip Mukherjee 2019-11-20 1350 goto err_release_driver;
8de47da07f8c6f drivers/tty/tty_io.c Sudip Mukherjee 2019-11-20 1351 }
04831dc154df9b drivers/tty/tty_io.c Jiri Slaby 2012-06-04 1352
5d4121c04b3577 drivers/tty/tty_io.c Jiri Slaby 2012-08-17 1353 WARN_RATELIMIT(!tty->port,
5d4121c04b3577 drivers/tty/tty_io.c Jiri Slaby 2012-08-17 1354 "%s: %s driver does not set tty->port. This will crash the kernel later. Fix the driver!\n",
5d4121c04b3577 drivers/tty/tty_io.c Jiri Slaby 2012-08-17 1355 __func__, tty->driver->name);
5d4121c04b3577 drivers/tty/tty_io.c Jiri Slaby 2012-08-17 1356
b027e2298bd588 drivers/tty/tty_io.c Gaurav Kohli 2018-01-23 1357 retval = tty_ldisc_lock(tty, 5 * HZ);
b027e2298bd588 drivers/tty/tty_io.c Gaurav Kohli 2018-01-23 1358 if (retval)
b027e2298bd588 drivers/tty/tty_io.c Gaurav Kohli 2018-01-23 1359 goto err_release_lock;
967fab6916681e drivers/tty/tty_io.c Jiri Slaby 2012-10-18 @1360 tty->port->itty = tty;
^^^^^^^^^^^^^^^^^^^^^^
Unchecked dereference.

967fab6916681e drivers/tty/tty_io.c Jiri Slaby 2012-10-18 1361

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