[PATCH v3 2/2] mmc: core: don't dereference parent when releasing host index

[Adriano Cordova]

mmc_host_classdev_release() reads host->parent->of_node to decide
whether to free the IDA slot, but mmc_alloc_host() does not guarantee
that the parent outlives the host (only devm_mmc_alloc_host() does).
So the vub300 driver can release its parent usb_device before
the host, resulting in a use-after-free.

Put the alias decision in host->index_is_alias at allocation time,
while the parent is still valid, and use it at release time.

Fixes: 10252bae863d ("mmc: core: Don't allocate IDA for OF aliases")
Reported-by: syzbot+f312381a95cc080992fd@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://syzkaller.appspot.com/bug?extid=f312381a95cc080992fd
Assisted-by: opencode: deepseek v4 flash
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Adriano Cordova <adrianox@xxxxxxxxx>
---
Changes since v1:
  - Added Assisted-by tag
  - put alias decision in host->index_is_alias
Changes since v2:
  - Split patch into two logical patches
  - Corrected the Fixes: tag

 drivers/mmc/core/host.c | 3 ++-
 include/linux/mmc/host.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index b7ce3137d452..542bb033c6da 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -67,7 +67,7 @@ static void mmc_host_classdev_release(struct device *dev)
 {
 	struct mmc_host *host = cls_dev_to_mmc_host(dev);
 	wakeup_source_unregister(host->ws);
-	if (of_alias_get_id(host->parent->of_node, "mmc") < 0)
+	if (!host->index_is_alias)
 		ida_free(&mmc_host_ida, host->index);
 	kfree(host);
 }
@@ -538,6 +538,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	}
 
 	host->index = index;
+	host->index_is_alias = (alias_id >= 0);
 
 	dev_set_name(&host->class_dev, "mmc%d", host->index);
 	host->ws = wakeup_source_register(NULL, dev_name(&host->class_dev));
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index ba84f02c2a10..165d24104d3c 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -356,6 +356,7 @@ struct mmc_host {
 	struct device		*parent;
 	struct device		class_dev;
 	int			index;
+	bool			index_is_alias;
 	const struct mmc_host_ops *ops;
 	struct mmc_pwrseq	*pwrseq;
 	unsigned int		f_min;
-- 
2.51.0