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Mon, 06 Jul 2026 19:52:51 -0700 (PDT) From: Zhao Li To: Johannes Berg Cc: linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] wifi: cfg80211: validate rx/tx MLME callback frame lengths before access Date: Tue, 7 Jul 2026 10:52:41 +0800 Message-ID: <20260707025241.22223-1-enderaoelyther@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <488ed9862d5196b8f5ecf23f037fa6725fbe9a52.camel@sipsolutions.net> References: <20260612185042.66260-4-enderaoelyther@gmail.com> <488ed9862d5196b8f5ecf23f037fa6725fbe9a52.camel@sipsolutions.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Mon, 2026-07-06 at 18:37 +0800, Johannes Berg wrote: > > Side effects of this change: > > - The WARN_ON(len < 2) is replaced by a silent early return, since > > these cfg80211 callbacks can legitimately receive short frames from > > drivers. > > Can they? How? You're right, that wording is wrong; no in-tree caller passes len < 2. mac80211 gates every path well above that (ieee80211_rx_mgmt_auth() at len < 24 + 6, ieee80211_rx_mgmt_deauth()/disassoc() at len < 24 + 2), and the locally built deauth/disassoc frames are always full size. The frames that do reach these callbacks undersized are short relative to their subtype, not shorter than 2 bytes. mwifiex accepts a 4-address ieee80211_hdr plus the 2-byte firmware length prefix. After it strips the prefix and removes addr4, pkt_len can be exactly 24: a bare 3-address management header with no reason-code body. WARN_ON(len < 2) does not fire on that, and cfg80211_process_deauth() then reads u.deauth.reason_code as a two-byte access starting at offset 24, immediately past the 24-byte buffer. So the len >= 2 check only guards the frame_control read; the per-subtype offsetofend() checks are the actual fix. I'll drop the WARN rather than keep it, because these are exported callbacks and a malformed frame from a driver should be dropped silently instead of backtraced. v2 rewrites the commit message to describe the mwifiex path instead of the inaccurate "legitimately receive short frames" claim; no code change. Thanks, Zhao Li