From fee2b871d8d6389c9b4bdf9346a99ccc1c98c9b8 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 12 Apr 2022 11:31:40 +0200 Subject: ALSA: core: Add snd_card_free_on_error() helper This is a small helper function to handle the error path more easily when an error happens during the probe for the device with the device-managed card. Since devres releases in the reverser order of the creations, usually snd_card_free() gets called at the last in the probe error path unless it already reached snd_card_register() calls. Due to this nature, when a driver expects the resource releases in card->private_free, this might be called too lately. As a workaround, one should call the probe like: static int __some_probe(...) { // do real probe.... } static int some_probe(...) { return snd_card_free_on_error(dev, __some_probe(dev, ...)); } so that the snd_card_free() is called explicitly at the beginning of the error path from the probe. This function will be used in the upcoming fixes to address the regressions by devres usages. Fixes: e8ad415b7a55 ("ALSA: core: Add managed card creation") Cc: Link: https://lore.kernel.org/r/20220412093141.8008-2-tiwai@suse.de Signed-off-by: Takashi Iwai --- sound/core/init.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) (limited to 'sound') diff --git a/sound/core/init.c b/sound/core/init.c index 31ba7024e3ad..726a8353201f 100644 --- a/sound/core/init.c +++ b/sound/core/init.c @@ -209,6 +209,12 @@ static void __snd_card_release(struct device *dev, void *data) * snd_card_register(), the very first devres action to call snd_card_free() * is added automatically. In that way, the resource disconnection is assured * at first, then released in the expected order. + * + * If an error happens at the probe before snd_card_register() is called and + * there have been other devres resources, you'd need to free the card manually + * via snd_card_free() call in the error; otherwise it may lead to UAF due to + * devres call orders. You can use snd_card_free_on_error() helper for + * handling it more easily. */ int snd_devm_card_new(struct device *parent, int idx, const char *xid, struct module *module, size_t extra_size, @@ -235,6 +241,28 @@ int snd_devm_card_new(struct device *parent, int idx, const char *xid, } EXPORT_SYMBOL_GPL(snd_devm_card_new); +/** + * snd_card_free_on_error - a small helper for handling devm probe errors + * @dev: the managed device object + * @ret: the return code from the probe callback + * + * This function handles the explicit snd_card_free() call at the error from + * the probe callback. It's just a small helper for simplifying the error + * handling with the managed devices. + */ +int snd_card_free_on_error(struct device *dev, int ret) +{ + struct snd_card *card; + + if (!ret) + return 0; + card = devres_find(dev, __snd_card_release, NULL, NULL); + if (card) + snd_card_free(card); + return ret; +} +EXPORT_SYMBOL_GPL(snd_card_free_on_error); + static int snd_card_init(struct snd_card *card, struct device *parent, int idx, const char *xid, struct module *module, size_t extra_size) -- cgit v1.2.3