[PATCH v2] ASoC: meson: Keep link pointers valid on realloc failure

[Linmao Li]

meson_card_reallocate_links() grows the DAI link and private data
arrays with two consecutive krealloc() calls and updates the owner
pointers only after both calls have succeeded.

A successful krealloc() may move the data: it frees the old block and
returns a new one. When that happens for the link array and the second
krealloc() then fails, card->dai_link still points to the block that
krealloc() already freed, and the error path frees the new block too.
The probe error path then calls meson_card_clean_references(), which
dereferences card->dai_link and kfree()s it again, resulting in a
use-after-free and a double free.

Commit card->dai_link and card->num_links right after the first
krealloc() succeeds, so the pointer always refers to a valid allocation
that meson_card_clean_references() can walk and free. krealloc() with
__GFP_ZERO zero-initializes the added entries, so walking them on the
error path is safe. With both failure paths reduced to a plain return,
drop the goto labels and the error message.

Fixes: 7864a79f37b5 ("ASoC: meson: add axg sound card support")
Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>
Reviewed-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
---
v2:
- also commit num_links together with dai_link (Jerome)
- drop the goto labels and the dev_err() (Jerome)
- comment the ldata failure path (Jerome)

 sound/soc/meson/meson-card-utils.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/sound/soc/meson/meson-card-utils.c b/sound/soc/meson/meson-card-utils.c
index cdb759b466ad..8617a4661a33 100644
--- a/sound/soc/meson/meson-card-utils.c
+++ b/sound/soc/meson/meson-card-utils.c
@@ -50,25 +50,20 @@ int meson_card_reallocate_links(struct snd_soc_card *card,
 			 num_links * sizeof(*priv->card.dai_link),
 			 GFP_KERNEL | __GFP_ZERO);
 	if (!links)
-		goto err_links;
+		return -ENOMEM;
+
+	priv->card.dai_link = links;
+	priv->card.num_links = num_links;
 
 	ldata = krealloc(priv->link_data,
 			 num_links * sizeof(*priv->link_data),
 			 GFP_KERNEL | __GFP_ZERO);
+	/* meson_card_clean_references() will free the links on this error path */
 	if (!ldata)
-		goto err_ldata;
+		return -ENOMEM;
 
-	priv->card.dai_link = links;
 	priv->link_data = ldata;
-	priv->card.num_links = num_links;
 	return 0;
-
-err_ldata:
-	kfree(links);
-err_links:
-	dev_err(priv->card.dev, "failed to allocate links\n");
-	return -ENOMEM;
-
 }
 EXPORT_SYMBOL_GPL(meson_card_reallocate_links);
 
-- 
2.25.1