linux-kernel - [PATCH] firmware: Fix security issue with request_firmware_into

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Date:   Fri, 31 Aug 2018 08:43:31 -0700
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     gregkh@...uxfoundation.org
Cc:     akpm@...ux-foundation.org, josh@...htriplett.org,
        rishabhb@...eaurora.org, kubakici@...pl, maco@...roid.com,
        andy.gross@...aro.org, david.brown@...aro.org,
        bjorn.andersson@...aro.org, linux-wireless@...r.kernel.org,
        keescook@...omium.org, shuah@...nel.org, mfuzzey@...keon.com,
        zohar@...ux.vnet.ibm.com, dhowells@...hat.com,
        pali.rohar@...il.com, tiwai@...e.de, arend.vanspriel@...adcom.com,
        zajec5@...il.com, nbroeking@...com, markivx@...eaurora.org,
        broonie@...nel.org, dmitry.torokhov@...il.com, dwmw2@...radead.org,
        torvalds@...ux-foundation.org, Abhay_Salunke@...l.com,
        jewalt@...innovations.com, cantabile.desu@...il.com, ast@...com,
        andresx7@...il.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, stable@...r.kernel.org,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: [PATCH] firmware: Fix security issue with request_firmware_into_buf()

From: Rishabh Bhatnagar <rishabhb@...eaurora.org>

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: 0e742e9275 ("firmware: provide infrastructure to make fw caching optional")
[mcgrof: broken since feature introduction on v4.8]

Cc: stable@...r.kernel.org # v4.8+
Signed-off-by: Vikram Mulukutla <markivx@...eaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@...eaurora.org>
Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---

This has been tested with the self test firmware scrip and found no
regressions.

 drivers/base/firmware_loader/main.c | 30 +++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 0943e7065e0e..b3c0498ee433 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/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;
 
-- 
2.18.0