linux-kernel - [PATCH wireless] wifi: iwlwifi: mvm: Fix a memory corruption issue

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Message-Id: <23f0ec986ef1529055f4f93dcb3940a6cf8d9a94.1690143750.git.christophe.jaillet@wanadoo.fr>
Date:   Sun, 23 Jul 2023 22:24:59 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Gregory Greenman <gregory.greenman@...el.com>,
        Kalle Valo <kvalo@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux-wireless@...r.kernel.org
Subject: [PATCH wireless] wifi: iwlwifi: mvm: Fix a memory corruption issue

A few lines above, space is kzalloc()'ed for:
	sizeof(struct iwl_nvm_data) +
	sizeof(struct ieee80211_channel) +
	sizeof(struct ieee80211_rate)

'mvm->nvm_data' is a 'struct iwl_nvm_data', so it is fine.

At the end of this structure, there is the 'channels' flex array.
Each element is of type 'struct ieee80211_channel'.
So only 1 element is allocated in this array.

When doing:
  mvm->nvm_data->bands[0].channels = mvm->nvm_data->channels;
We point at the first element of the 'channels' flex array.
So this is fine.

However, when doing:
  mvm->nvm_data->bands[0].bitrates =
			(void *)((u8 *)mvm->nvm_data->channels + 1);
because of the "(u8 *)" cast, we add only 1 to the address of the beginning
of the flex array.

It is likely that we want point at the 'struct ieee80211_rate' allocated
just after.

Remove the spurious casting so that the pointer arithmetic works as
expected.

Fixes: 8ca151b568b6 ("iwlwifi: add the MVM driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
I've checked in the .s files, and :

Before
======
# drivers/net/wireless/intel/iwlwifi/mvm/fw.c:801: 		mvm->nvm_data->bands[0].channels = mvm->nvm_data->channels;
	leaq	1448(%r13), %rax	#, tmp248

# drivers/net/wireless/intel/iwlwifi/mvm/fw.c:805: 			(void *)((u8 *)mvm->nvm_data->channels + 1);
	leaq	1449(%r13), %rax	#, tmp252


After:
=====
# drivers/net/wireless/intel/iwlwifi/mvm/fw.c:801: 		mvm->nvm_data->bands[0].channels = mvm->nvm_data->channels;
	leaq	1448(%r13), %rax	#, tmp248

# drivers/net/wireless/intel/iwlwifi/mvm/fw.c:805: 			(void *)(mvm->nvm_data->channels + 1);
	leaq	1512(%r13), %rax	#, tmp252

And on my system sizeof(struct ieee80211_channel) = 64

/!\ This patch is only speculative and untested. /!\

It is strange that a memory corruption issue has been un-noticed for more
than 10 years.

So review with care.
---
 drivers/net/wireless/intel/iwlwifi/mvm/fw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/fw.c b/drivers/net/wireless/intel/iwlwifi/mvm/fw.c
index 1f5db65a088d..1d5ee4330f29 100644
--- a/drivers/net/wireless/intel/iwlwifi/mvm/fw.c
+++ b/drivers/net/wireless/intel/iwlwifi/mvm/fw.c
@@ -802,7 +802,7 @@ int iwl_run_init_mvm_ucode(struct iwl_mvm *mvm)
 		mvm->nvm_data->bands[0].n_channels = 1;
 		mvm->nvm_data->bands[0].n_bitrates = 1;
 		mvm->nvm_data->bands[0].bitrates =
-			(void *)((u8 *)mvm->nvm_data->channels + 1);
+			(void *)(mvm->nvm_data->channels + 1);
 		mvm->nvm_data->bands[0].bitrates->hw_value = 10;
 	}
 
-- 
2.34.1