Subject: Re: Coverity: iwl_mvm_sec_key_add(): Memory - corruptions

From: Kees Cook <[email-masked]>
Date: Fri, 18 Nov 2022 14:25:22 -0800

On Fri, Nov 18, 2022 at 10:04:38PM +0100, Johannes Berg wrote:
> On Fri, 2022-11-18 at 08:54 -0800, coverity-bot wrote:
> > 
> > *** CID 1527370:  Memory - corruptions  (OVERRUN)
> > drivers/net/wireless/intel/iwlwifi/mvm/mld-key.c:123 in iwl_mvm_sec_key_add()
> > 117
> > 118     	if (WARN_ON(keyconf->keylen > sizeof(cmd.u.add.key)))
> > 119     		return -EINVAL;
> > 120
> > 121     	if (keyconf->cipher == WLAN_CIPHER_SUITE_WEP40 ||
> > 122     	    keyconf->cipher == WLAN_CIPHER_SUITE_WEP104)
> > vvv     CID 1527370:  Memory - corruptions  (OVERRUN)
> > vvv     Overrunning buffer pointed to by "cmd.u.add.key + 3" of 32 bytes by passing it to a function which accesses it at byte offset 34 using argument "keyconf->keylen" (which evaluates to 32). [Note: The source code implementation of the function has been overridden by a builtin model.]
> > 123     		memcpy(cmd.u.add.key + IWL_SEC_WEP_KEY_OFFSET, keyconf->key,
> > 124     		       keyconf->keylen);
> > 125     	else
> > 126     		memcpy(cmd.u.add.key, keyconf->key, keyconf->keylen);
> > 127
> > 128     	if (keyconf->cipher == WLAN_CIPHER_SUITE_TKIP) {
> > 
> > If this is a false positive, please let us know so we can mark it as
> > such, or teach the Coverity rules to be smarter. If not, please make
> > sure fixes get into linux-next. :) For patches fixing this, please
> > include these lines (but double-check the "Fixes" first):
> > 
> 
> Well, I don't think you can teach coverity this easily, but the
> WARN_ON() check there is not really meant to protect this - WEP keys
> must have a length of either 5 or 13 bytes (40 or 104 bits!).
> 
> So there's no issue here, but I'm not surprised that coverity wouldn't
> be able to figure that out through the stack.

Gotcha. And some other layer is doing the verification that cipher and
keylen are correctly matched?

-- 
Kees Cook