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Sat, 18 Jul 2026 12:02:24 -0700 (PDT) From: Muhammad Bilal To: Greg Kroah-Hartman Cc: linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Muhammad Bilal Subject: [PATCH 5/5] staging: rtl8723bs: fix skb->len underflow in monitor TX path Date: Sun, 19 Jul 2026 00:02:12 +0500 Message-ID: <20260718190212.64409-1-meatuni001@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260718185445.63070-1-meatuni001@gmail.com> References: <20260718185445.63070-1-meatuni001@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit rtw_cfg80211_monitor_if_xmit_entry() strips a radiotap header with skb_pull(skb, rtap_len), then immediately dereferences the 802.11 header fields (frame_control, addr1, addr2) without checking that skb->len is still large enough to contain a struct ieee80211_hdr (24 bytes). Further down, it calls: skb_pull(skb, dot11_hdr_len + qos_len + snap_len - sizeof(src_mac_addr) * 2); again with no check that skb->len covers this amount first. Plain skb_pull() does not itself validate the requested length against skb->len; on a too-short injected frame this makes skb->len underflow to a huge unsigned value, after which skb->data and the following memcpy()s operate on a corrupted skb. This function is reachable by writing a raw frame to a monitor-mode network device, which does not require elevated privileges beyond being able to create/use a monitor-mode interface (CAP_NET_RAW). Add explicit skb->len checks before dereferencing the 802.11 header and before each skb_pull(), bailing out via the existing "fail" error path on any mismatch. Fixes: 554c0a3abf216 ("staging: Add rtl8723bs sdio wifi driver") Cc: stable@vger.kernel.org Signed-off-by: Muhammad Bilal --- drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c b/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c index 6a97afd89dc7..eac1b6ac4c67 100644 --- a/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c +++ b/drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c @@ -2034,10 +2034,15 @@ static netdev_tx_t rtw_cfg80211_monitor_if_xmit_entry(struct sk_buff *skb, struc /* Skip the ratio tap header */ skb_pull(skb, rtap_len); + if (unlikely(skb->len < sizeof(struct ieee80211_hdr))) + goto fail; + dot11_hdr = (struct ieee80211_hdr *)skb->data; frame_control = le16_to_cpu(dot11_hdr->frame_control); /* Check if the QoS bit is set */ if ((frame_control & IEEE80211_FCTL_FTYPE) == IEEE80211_FTYPE_DATA) { + int pull_len; + /* Check if this ia a Wireless Distribution System (WDS) frame * which has 4 MAC addresses */ @@ -2046,13 +2051,19 @@ static netdev_tx_t rtw_cfg80211_monitor_if_xmit_entry(struct sk_buff *skb, struc if ((frame_control & 0x0300) == 0x0300) dot11_hdr_len += 6; + if (unlikely(skb->len < dot11_hdr_len + qos_len)) + goto fail; + memcpy(dst_mac_addr, dot11_hdr->addr1, sizeof(dst_mac_addr)); memcpy(src_mac_addr, dot11_hdr->addr2, sizeof(src_mac_addr)); /* Skip the 802.11 header, QoS (if any) and SNAP, but leave spaces for * two MAC addresses */ - skb_pull(skb, dot11_hdr_len + qos_len + snap_len - sizeof(src_mac_addr) * 2); + pull_len = dot11_hdr_len + qos_len + snap_len - sizeof(src_mac_addr) * 2; + if (unlikely(pull_len < 0 || skb->len < pull_len)) + goto fail; + skb_pull(skb, pull_len); pdata = (unsigned char *)skb->data; memcpy(pdata, dst_mac_addr, sizeof(dst_mac_addr)); memcpy(pdata + sizeof(dst_mac_addr), src_mac_addr, sizeof(src_mac_addr)); -- 2.55.0