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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e36115cc8sm9018249a91.3.2026.09.18.00.58.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2026 00:58:30 -0700 (PDT) From: Hui Peng To: Marcel Holtmann , Luiz Augusto von Dentz Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, Hui Peng Subject: [PATCH] Bluetooth: RFCOMM: Reject short EA=0 frames in rfcomm_recv_frame() Date: Fri, 18 Sep 2026 07:58:28 +0000 Message-ID: <20260918075829.2203887-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit While rfcomm_recv_frame() verifies that skb->len is at least sizeof(*hdr) + 1 (4 bytes: 3-byte header + 1-byte FCS), an RFCOMM frame with an extended 2-byte length field (!__test_ea(hdr->len)) has a 4-byte header plus a 1-byte FCS (5 bytes minimum, sizeof(*hdr) + 2). When a 4-byte RFCOMM frame with EA == 0 arrives: 1. The initial skb->len < sizeof(*hdr) + 1 check passes (4 < 4 is false). 2. Trimming the FCS byte decrements skb->len to 3. 3. If __check_fcs() succeeds, skb_pull(skb, 4) fails (4 > 3) and returns NULL without advancing skb->data. 4. Because the return value of skb_pull() is ignored, the un-pulled 3-byte struct rfcomm_hdr remains at skb->data and is either queued as application payload via rfcomm_recv_data() or parsed as a multiplexer control command via rfcomm_recv_mcc() on DLCI 0. Fix this by extending the length check in rfcomm_recv_frame() to also require skb->len >= sizeof(*hdr) + 2 when !__test_ea(hdr->len). Signed-off-by: Hui Peng --- net/bluetooth/rfcomm/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c index f7463f092..d91e2a6ee 100644 --- a/net/bluetooth/rfcomm/core.c +++ b/net/bluetooth/rfcomm/core.c @@ -1817,7 +1817,8 @@ static struct rfcomm_session *rfcomm_recv_frame(struct rfcomm_session *s, return s; } - if (skb->len < sizeof(*hdr) + 1) { + if (skb->len < sizeof(*hdr) + 1 || + (!__test_ea(hdr->len) && skb->len < sizeof(*hdr) + 2)) { kfree_skb(skb); return s; } -- 2.55.0.1082.g2b9226bbc0-goog