netdev - Re: [PATCH net v3 3/3] nfc: st21nfca: fix incorrect sizing calculations in EVT

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Message-ID: <9d387882-3c9a-5056-9ee3-81ab6ea0a9a6@linaro.org>
Date:   Wed, 8 Jun 2022 09:09:55 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Martin Faltesek <mfaltesek@...gle.com>, kuba@...nel.org
Cc:     christophe.ricard@...il.com, gregkh@...uxfoundation.org,
        groeck@...gle.com, jordy@...ing.systems, krzk@...nel.org,
        martin.faltesek@...il.com, netdev@...r.kernel.org,
        linux-nfc@...ts.01.org, sameo@...ux.intel.com, wklin@...gle.com,
        theflamefire89@...il.com, stable@...r.kernel.org
Subject: Re: [PATCH net v3 3/3] nfc: st21nfca: fix incorrect sizing
 calculations in EVT_TRANSACTION

On 07/06/2022 04:57, Martin Faltesek wrote:
> The transaction buffer is allocated by using the size of the packet buf,
> and subtracting two which seem intended to remove the two tags which are
> not present in the target structure. This calculation leads to under
> counting memory because of differences between the packet contents and the
> target structure. The aid_len field is a u8 in the packet, but a u32 in
> the structure, resulting in at least 3 bytes always being under counted.
> Further, the aid data is a variable length field in the packet, but fixed
> in the structure, so if this field is less than the max, the difference is
> added to the under counting.
> 
> The last validation check for transaction->params_len is also incorrect
> since it employs the same accounting error.
> 
> To fix, perform validation checks progressively to safely reach the
> next field, to determine the size of both buffers and verify both tags.
> Once all validation checks pass, allocate the buffer and copy the data.
> This eliminates freeing memory on the error path, as those checks are
> moved ahead of memory allocation.
> 
> Fixes: 26fc6c7f02cb ("NFC: st21nfca: Add HCI transaction event support")
> Fixes: 4fbcc1a4cb20 ("nfc: st21nfca: Fix potential buffer overflows in EVT_TRANSACTION")
> Cc: stable@...r.kernel.org
> Signed-off-by: Martin Faltesek <mfaltesek@...gle.com>
> ---

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>


Best regards,
Krzysztof