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Fri, 06 Feb 2026 07:12:30 -0800 (PST) Date: Fri, 6 Feb 2026 16:12:17 +0100 From: Stephan Gerhold To: Dan Carpenter Cc: Stephan Gerhold , Johannes Berg , netdev@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel Subject: Re: [bug report] net: wwan: Add Qualcomm BAM-DMUX WWAN network driver Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Dan, On Fri, Feb 06, 2026 at 04:38:30PM +0300, Dan Carpenter wrote: > [ Smatch checking is paused while we raise funding. #SadFace > https://lore.kernel.org/all/aTaiGSbWZ9DJaGo7@stanley.mountain/ -dan ] > > Hello Stephan Gerhold, > > Commit 21a0ffd9b38c ("net: wwan: Add Qualcomm BAM-DMUX WWAN network > driver") from Nov 27, 2021 (linux-next), leads to the following > Smatch static checker warning: > > drivers/net/wwan/qcom_bam_dmux.c:505 bam_dmux_cmd_data() > error: buffer overflow 'dmux->netdevs' 8 <= 255 user_rl='0-255' uncapped > > drivers/net/wwan/qcom_bam_dmux.c > 500 static void bam_dmux_cmd_data(struct bam_dmux_skb_dma *skb_dma) > 501 { > 502 struct bam_dmux *dmux = skb_dma->dmux; > 503 struct sk_buff *skb = skb_dma->skb; > 504 struct bam_dmux_hdr *hdr = (struct bam_dmux_hdr *)skb->data; > --> 505 struct net_device *netdev = dmux->netdevs[hdr->ch]; > ^^^^^^^ > Smatch thinks skb->data is untrusted. This is the rx path. > Thanks a lot for the report! I believe this is not a problem in practice, since there is an existing check for this in bam_dmux_rx_callback() (which is the only function that calls bam_dmux_cmd_data()): if (hdr->ch >= BAM_DMUX_NUM_CH) { dev_dbg(dmux->dev, "Unsupported channel: %u\n", hdr->ch); goto out; } switch (hdr->cmd) { case BAM_DMUX_CMD_DATA: bam_dmux_cmd_data(skb_dma); break; Is that something Smatch should be able to detect? Thanks, Stephan