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: 0e742e9275 ("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>

1 files 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;