[PATCH] interconnect: Fix use after free in icc_get() and of_icc_get_by_index()

[Kuan-Wei Chiu]

In of_icc_get_by_index() and icc_get(), if the dynamic allocation for
path->name fails via kasprintf(), the error handling path directly
calls kfree(path) to free the path object and returns an error.

However, prior to this point, path_find() calls path_init(), which
already links the path's requests into the req_list of the respective
interconnect nodes via hlist_add_head(). Directly invoking kfree(path)
leaves dangling pointers in the hlist. A subsequent call to icc_get()
or icc_set_bw() will traverse or modify these corrupted lists, triggering
a slab use afterfree.

KASAN report showing the vulnerability when reproducing via debugfs:

  BUG: KASAN: slab-use-after-free in path_find+0x6f8/0xcfc
  Write of size 8 at addr fff000000d43f748 by task sh/1
  ...
  Call trace:
   kasan_report+0xac/0xfc
   path_find+0x6f8/0xcfc
   icc_get+0x148/0x380
   icc_get_set+0xf8/0x2d0
  ...
  Freed by task 1:
   kfree+0x1a0/0x4a4
   icc_get+0x2cc/0x380
   icc_get_set+0xf8/0x2d0

Fix this by replacing kfree(path) with the proper teardown function,
icc_put(path), which safely removes the requests from the req_list using
hlist_del() and drops the provider usage references before freeing the
memory.

Additionally, in icc_get(), ensure that the icc_lock mutex is released
prior to calling icc_put(path) to avoid a deadlock, as icc_put()
internally acquires the same lock.

Fixes: 3791163602f7 ("interconnect: Handle memory allocation errors")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
---
I discovered this bug while reviewing Krzysztof's patch [1]. 
To verify my hypothesis, I injected an artificial kasprintf() failure
into  the source code and wrote a minimal dummy icc provider module.
This allowed  me to successfully trigger the use after free via the
debugfs client and catch it with KASAN, confirming the issue.

[1]: https://lore.kernel.org/lkml/20260416130912.375013-2-krzysztof.kozlowski@xxxxxxxxxxxxxxxx/

 drivers/interconnect/core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
index 8569b78a1851..e14280ced381 100644
--- a/drivers/interconnect/core.c
+++ b/drivers/interconnect/core.c
@@ -528,7 +528,7 @@ struct icc_path *of_icc_get_by_index(struct device *dev, int idx)
 	path->name = kasprintf(GFP_KERNEL, "%s-%s",
 			       src_data->node->name, dst_data->node->name);
 	if (!path->name) {
-		kfree(path);
+		icc_put(path);
 		path = ERR_PTR(-ENOMEM);
 	}
 
@@ -626,8 +626,9 @@ struct icc_path *icc_get(struct device *dev, const char *src, const char *dst)
 
 	path->name = kasprintf(GFP_KERNEL, "%s-%s", src_node->name, dst_node->name);
 	if (!path->name) {
-		kfree(path);
-		path = ERR_PTR(-ENOMEM);
+		mutex_unlock(&icc_lock);
+		icc_put(path);
+		return ERR_PTR(-ENOMEM);
 	}
 out:
 	mutex_unlock(&icc_lock);
-- 
2.54.0.rc1.555.g9c883467ad-goog