firmware: Fix security issue with request_firmware_into_buf()

When calling request_firmware_into_buf() with the FW_OPT_NOCACHE flag
it is expected that firmware is loaded into buffer from memory.
But inside alloc_lookup_fw_priv every new firmware that is loaded is
added to the firmware cache (fwc) list head. So if any driver requests
a firmware that is already loaded the code iterates over the above
mentioned list and it can end up giving a pointer to other device driver's
firmware buffer.
Also the existing copy may either be modified by drivers, remote processors
or even freed. This causes a potential security issue with batched requests
when using request_firmware_into_buf.

Fix alloc_lookup_fw_priv to not add to the fwc head list if FW_OPT_NOCACHE
is set, and also don't do the lookup in the list.

Fixes: 0e742e92 ("firmware: provide infrastructure to make fw caching optional")
[mcgrof: broken since feature introduction on v4.8]

Cc: stable@vger.kernel.org # v4.8+
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/firmware_loader/main.c

@@ -209,21 +209,24 @@ static struct fw_priv *__lookup_fw_priv(const char *fw_name)
 static int alloc_lookup_fw_priv(const char *fw_name,
 				struct firmware_cache *fwc,
 				struct fw_priv **fw_priv, void *dbuf,
-				size_t size)
+				size_t size, enum fw_opt opt_flags)
 {
 	struct fw_priv *tmp;
 
 	spin_lock(&fwc->lock);
-	tmp = __lookup_fw_priv(fw_name);
-	if (tmp) {
-		kref_get(&tmp->ref);
-		spin_unlock(&fwc->lock);
-		*fw_priv = tmp;
-		pr_debug("batched request - sharing the same struct fw_priv and lookup for multiple requests\n");
-		return 1;
+	if (!(opt_flags & FW_OPT_NOCACHE)) {
+		tmp = __lookup_fw_priv(fw_name);
+		if (tmp) {
+			kref_get(&tmp->ref);
+			spin_unlock(&fwc->lock);
+			*fw_priv = tmp;
+			pr_debug("batched request - sharing the same struct fw_priv and lookup for multiple requests\n");
+			return 1;
+		}
 	}
+
 	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size);
-	if (tmp)
+	if (tmp && !(opt_flags & FW_OPT_NOCACHE))
 		list_add(&tmp->list, &fwc->head);
 	spin_unlock(&fwc->lock);
 
@@ -493,7 +496,8 @@ int assign_fw(struct firmware *fw, struct device *device,
  */
 static int
 _request_firmware_prepare(struct firmware **firmware_p, const char *name,
-			  struct device *device, void *dbuf, size_t size)
+			  struct device *device, void *dbuf, size_t size,
+			  enum fw_opt opt_flags)
 {
 	struct firmware *firmware;
 	struct fw_priv *fw_priv;
@@ -511,7 +515,8 @@ _request_firmware_prepare(struct firmware **firmware_p, const char *name,
 		return 0; /* assigned */
 	}
 
-	ret = alloc_lookup_fw_priv(name, &fw_cache, &fw_priv, dbuf, size);
+	ret = alloc_lookup_fw_priv(name, &fw_cache, &fw_priv, dbuf, size,
+				  opt_flags);
 
 	/*
 	 * bind with 'priv' now to avoid warning in failure path
@@ -571,7 +576,8 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
 		goto out;
 	}
 
-	ret = _request_firmware_prepare(&fw, name, device, buf, size);
+	ret = _request_firmware_prepare(&fw, name, device, buf, size,
+					opt_flags);
 	if (ret <= 0) /* error or already assigned */
 		goto out;