linux-kernel - Re: [PATCH] wifi: mwifiex: Fix memcpy() field-spanning write warning in mwifiex_config

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Message-ID: <4e926821-de7c-4618-be73-e95965bef3b5@embeddedor.com>
Date: Tue, 17 Sep 2024 20:21:32 +0200
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Jeff Johnson <quic_jjohnson@...cinc.com>,
 Alper Nebi Yasak <alpernebiyasak@...il.com>, linux-wireless@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: David Lin <yu-hao.lin@....com>, Dmitry Antipov <dmantipov@...dex.ru>,
 Brian Norris <briannorris@...omium.org>, Kalle Valo <kvalo@...nel.org>,
 Francesco Dolcini <francesco@...cini.it>,
 Sascha Hauer <s.hauer@...gutronix.de>, Kees Cook <kees@...nel.org>,
 "Gustavo A . R . Silva" <gustavoars@...nel.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH] wifi: mwifiex: Fix memcpy() field-spanning write warning
 in mwifiex_config_scan()



On 17/09/24 20:10, Jeff Johnson wrote:
> On 9/17/2024 8:08 AM, Alper Nebi Yasak wrote:
>> Replace one-element array with a flexible-array member in `struct
>> mwifiex_ie_types_wildcard_ssid_params` to fix the following warning
>> on a MT8173 Chromebook (mt8173-elm-hana):
>>
>> [  356.775250] ------------[ cut here ]------------
>> [  356.784543] memcpy: detected field-spanning write (size 6) of single field "wildcard_ssid_tlv->ssid" at drivers/net/wireless/marvell/mwifiex/scan.c:904 (size 1)
>> [  356.813403] WARNING: CPU: 3 PID: 742 at drivers/net/wireless/marvell/mwifiex/scan.c:904 mwifiex_scan_networks+0x4fc/0xf28 [mwifiex]
>>
>> The "(size 6)" above is exactly the length of the SSID of the network
>> this device was connected to. The source of the warning looks like:
>>
>>      ssid_len = user_scan_in->ssid_list[i].ssid_len;
>>      [...]
>>      memcpy(wildcard_ssid_tlv->ssid,
>>             user_scan_in->ssid_list[i].ssid, ssid_len);
>>
>> Also adjust a #define that uses sizeof() on this struct to keep the
>> value same as before.
>>
>> Signed-off-by: Alper Nebi Yasak <alpernebiyasak@...il.com>
>> ---
>> I found these relevant patches that modify other such arrays, where the
>> second one removes a -1 from some sizeof() calculation:
>>
>> https://lore.kernel.org/lkml/Y9xkECG3uTZ6T1dN@work/T/#u
>> https://lore.kernel.org/lkml/ZsZa5xRcsLq9D+RX@elsanto/T/#u
>>
>> So I think we need the +1 to keep things same. But it appears to work
>> fine without it, so I'm not sure. Maybe it should've had a -1 before
>> that I would remove with this?
> 
> I think the original code was incorrect and was allocating too much memory.
> I do not think WILDCARD_SSID_TLV_MAX_SIZE requires modification.

If this is case, I think the changelog text should include the following
'Fixes' tag (and the `__counted_by` annotation added in a separate patch):

Fixes: 5e6e3a92b9a4 ("wireless: mwifiex: initial commit for Marvell mwifiex driver")

Thanks
--
Gustavo

> 
>>
>>   drivers/net/wireless/marvell/mwifiex/fw.h   | 2 +-
>>   drivers/net/wireless/marvell/mwifiex/scan.c | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/wireless/marvell/mwifiex/fw.h b/drivers/net/wireless/marvell/mwifiex/fw.h
>> index d03129d5d24e..4a96281792cc 100644
>> --- a/drivers/net/wireless/marvell/mwifiex/fw.h
>> +++ b/drivers/net/wireless/marvell/mwifiex/fw.h
>> @@ -875,7 +875,7 @@ struct mwifiex_ietypes_chanstats {
>>   struct mwifiex_ie_types_wildcard_ssid_params {
>>   	struct mwifiex_ie_types_header header;
>>   	u8 max_ssid_length;
>> -	u8 ssid[1];
>> +	u8 ssid[];
>>   } __packed;
>>   
>>   #define TSF_DATA_SIZE            8
>> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
>> index cab889af4c4a..50af78ee935b 100644
>> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
>> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
>> @@ -32,7 +32,7 @@
>>   #define WILDCARD_SSID_TLV_MAX_SIZE  \
>>   	(MWIFIEX_MAX_SSID_LIST_LENGTH *					\
>>   		(sizeof(struct mwifiex_ie_types_wildcard_ssid_params)	\
>> -			+ IEEE80211_MAX_SSID_LEN))
>> +			+ IEEE80211_MAX_SSID_LEN + 1))
>>   
>>   /* Maximum memory needed for a mwifiex_scan_cmd_config with all TLVs at max */
>>   #define MAX_SCAN_CFG_ALLOC (sizeof(struct mwifiex_scan_cmd_config)        \
>>
>> base-commit: 4f3e012d4cfd1d9bf837870c961f462ca9f23ebe
>