[PATCH 1/1] firmware: fix use-after-free in _request_firmware()

* [PATCH 1/1] firmware: fix use-after-free in _request_firmware()
@ 2021-07-13  2:49 Zhen Lei
  2021-07-16 19:56 ` Luis Chamberlain
  0 siblings, 1 reply; 5+ messages in thread
From: Zhen Lei @ 2021-07-13  2:49 UTC (permalink / raw)
  To: Luis Chamberlain, Greg Kroah-Hartman, Rafael J . Wysocki,
	Ming Lei, linux-kernel
  Cc: Zhen Lei

		CPU0			CPU1
__device_uncache_fw_images():		assign_fw():
					fw_cache_piggyback_on_request()
					<----- P0
	spin_lock(&fwc->name_lock);
	...
	list_del(&fce->list);
	spin_unlock(&fwc->name_lock);

	uncache_firmware(fce->name);
					<----- P1
					kref_get(&fw_priv->ref);

If CPU1 is interrupted at position P0, the new 'fce' has been added to the
list fwc->fw_names by the fw_cache_piggyback_on_request(). In this case,
CPU0 executes __device_uncache_fw_images() and will be able to see it when
it traverses list fwc->fw_names. Before CPU1 executes kref_get() at P1, if
CPU0 further executes uncache_firmware(), the count of fw_priv->ref may
decrease to 0, causing fw_priv to be released in advance.

Move kref_get() to the lock protection range of fwc->name_lock to fix it.

Fixes: ac39b3ea73aa ("firmware loader: let caching firmware piggyback on loading firmware")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 drivers/base/firmware_loader/main.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 4fdb8219cd08..2f267b8d2fd9 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -165,7 +165,7 @@ static inline int fw_state_wait(struct fw_priv *fw_priv)
 	return __fw_state_wait_common(fw_priv, MAX_SCHEDULE_TIMEOUT);
 }
 
-static int fw_cache_piggyback_on_request(const char *name);
+static void fw_cache_piggyback_on_request(struct fw_priv *fw_priv);
 
 static struct fw_priv *__allocate_fw_priv(const char *fw_name,
 					  struct firmware_cache *fwc,
@@ -707,10 +707,8 @@ int assign_fw(struct firmware *fw, struct device *device)
 	 * on request firmware.
 	 */
 	if (!(fw_priv->opt_flags & FW_OPT_NOCACHE) &&
-	    fw_priv->fwc->state == FW_LOADER_START_CACHE) {
-		if (fw_cache_piggyback_on_request(fw_priv->fw_name))
-			kref_get(&fw_priv->ref);
-	}
+	    fw_priv->fwc->state == FW_LOADER_START_CACHE)
+		fw_cache_piggyback_on_request(fw_priv);
 
 	/* pass the pages buffer to driver at the last minute */
 	fw_set_page_data(fw_priv, fw);
@@ -1257,11 +1255,11 @@ static int __fw_entry_found(const char *name)
 	return 0;
 }
 
-static int fw_cache_piggyback_on_request(const char *name)
+static void fw_cache_piggyback_on_request(struct fw_priv *fw_priv)
 {
-	struct firmware_cache *fwc = &fw_cache;
+	const char *name = fw_priv->fw_name;
+	struct firmware_cache *fwc = fw_priv->fwc;
 	struct fw_cache_entry *fce;
-	int ret = 0;
 
 	spin_lock(&fwc->name_lock);
 	if (__fw_entry_found(name))
@@ -1269,13 +1267,12 @@ static int fw_cache_piggyback_on_request(const char *name)
 
 	fce = alloc_fw_cache_entry(name);
 	if (fce) {
-		ret = 1;
 		list_add(&fce->list, &fwc->fw_names);
+		kref_get(&fw_priv->ref);
 		pr_debug("%s: fw: %s\n", __func__, name);
 	}
 found:
 	spin_unlock(&fwc->name_lock);
-	return ret;
 }
 
 static void free_fw_cache_entry(struct fw_cache_entry *fce)
@@ -1506,9 +1503,8 @@ static inline void unregister_fw_pm_ops(void)
 	unregister_pm_notifier(&fw_cache.pm_notify);
 }
 #else
-static int fw_cache_piggyback_on_request(const char *name)
+static void fw_cache_piggyback_on_request(struct fw_priv *fw_priv)
 {
-	return 0;
 }
 static inline int register_fw_pm_ops(void)
 {
-- 
2.25.1


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