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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Mark Greer , Simon Horman , oe-linux-nfc@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net v3] nfc: digital: check DEP_REQ length before reading DID byte Date: Sun, 13 Sep 2026 22:07:19 +0100 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: LO4P123CA0425.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:18b::16) To AS8P251MB0001.EURP251.PROD.OUTLOOK.COM (2603:10a6:20b:344::22) X-Microsoft-Original-Message-ID: <20260913210719.12057-1-elb12345@hotmail.co.uk> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AS8P251MB0001:EE_|AS8P251MB0760:EE_ X-MS-Office365-Filtering-Correlation-Id: b6b64bd6-0fa9-4fac-4743-08df11dafffe X-Microsoft-Antispam: BCL:0;ARA:14566002|4140399003|23021999003|25010399006|15080799012|25031999004|37011999003|8060799015|12121999013|51005399006|19110799012|5072599009|55001999006|24021099003|41001999006|40105399003|1602099012|10035399007|2607281247196008|4302099013|3412199025|440099028|26104999009; 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A crafted DEP_REQ that is > exactly 3 bytes long with the DID bit set causes an out-of-bounds read > past the valid skb data. > > This read can happen on every DEP_REQ from a malicious NFC initiator > when the target device has a non-zero DID. The stale byte is compared > against ddev->did, so in practice the mismatch causes an -EIO return, > but the read itself is undefined behavior and accesses data past the > buffer. > > Reorder the condition so that the length check (resp->len < size + 1) > comes first and short-circuits before resp->data[size] is accessed. > The later "size > resp->len" check becomes redundant and is left in > place. > > Fixes: 05afedcb8918 ("NFC: digital: Add Target-mode NFC-DEP DID Support") +Cc Mark Greer, author of 05afedcb8918, which the Fixes: tag in this version points at. I missed adding him when correcting the tag. > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Aamir Ahmed > Reviewed-by: Simon Horman > --- > v3: > - correct the Fixes: tag; the bug came in with 05afedcb8918 > - reword the note on the later "size > resp->len" check, which > returns early for NAD frames and is now redundant rather than > preserved for that case > No code change; Simon's Reviewed-by carried. > v2: https://lore.kernel.org/netdev/AS8P251MB0001F45C42BBD0D16D7B30ABC8BD2@AS8P251MB0001.EURP251.PROD.OUTLOOK.COM/ > - add the Assisted-by: LLM tag (Simon) > - designate the target tree in the subject > - collect Simon's Reviewed-by > v1: https://lore.kernel.org/netdev/AS8P251MB000196084524EB27D62162B8C8B32@AS8P251MB0001.EURP251.PROD.OUTLOOK.COM/ > > Compile-tested only; I have no NFC hardware. > > net/nfc/digital_dep.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/net/nfc/digital_dep.c b/net/nfc/digital_dep.c > index 3982fa084737..ae5407fca12d 100644 > --- a/net/nfc/digital_dep.c > +++ b/net/nfc/digital_dep.c > @@ -1117,12 +1117,12 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg, > pfb = dep_req->pfb; > > if (DIGITAL_NFC_DEP_DID_BIT_SET(pfb)) { > - if (ddev->did && (ddev->did == resp->data[3])) { > - size++; > - } else { > + if (resp->len < size + 1 || !ddev->did || > + ddev->did != resp->data[size]) { > rc = -EIO; > goto exit; > } > + size++; > } else if (ddev->did) { > rc = -EIO; > goto exit; > > base-commit: df2908090cda368b01ff43709f51890076c56157 Kind Regards Aamir A.