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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e6c6dd585sm5802399a91.0.2026.09.19.14.28.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 14:28:55 -0700 (PDT) From: Hui Peng To: alex.aring@gmail.com, stefan@datenfreihafen.org, miquel.raynal@bootlin.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Cc: horms@kernel.org, linux-wpan@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] ieee802154: socket: fix shared skb BUG_ON and double header subtraction in dgram_ioctl() Date: Sat, 19 Sep 2026 21:28:55 +0000 Message-ID: <20260919212855.3241205-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-wpan@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In `dgram_ioctl()` (`SIOCINQ`), the queued skb at the head of `sk->sk_receive_queue` has already had its MAC header stripped by `ieee802154_subif_frame()` prior to `dgram_deliver()`, so `skb->len` is already the exact payload length that `dgram_recvmsg()` will return to userspace. However, `dgram_ioctl()` computes `*karg = skb->len - ieee802154_hdr_length(skb)`. Calling `ieee802154_hdr_length(skb)` re-parses the payload bytes as an 802.15.4 MAC header and calls `pskb_may_pull(skb, ...)` while holding `sk->sk_receive_queue.lock`. When multiple `SOCK_DGRAM` sockets receive a cloned copy of the frame (`skb_shared(skb)` is true) and the payload is non-linear, `pskb_may_pull()` calls `pskb_expand_head()`, which triggers `BUG_ON(skb_shared(skb))`. Even on unshared linear skbs, subtracting `ieee802154_hdr_length(skb)` a second time underflows `*karg` to a negative value when the payload is shorter than the bogus parsed header length. Set `*karg = skb->len` directly in `dgram_ioctl()`. Fixes: e1d001fa5b47 ("net: ioctl: Use kernel memory on protocol ioctl callbacks") Assisted-by: LLM Signed-off-by: Hui Peng --- net/ieee802154/socket.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ieee802154/socket.c b/net/ieee802154/socket.c index 5a36e87893f6..8d660fe87d4e 100644 --- a/net/ieee802154/socket.c +++ b/net/ieee802154/socket.c @@ -552,7 +552,7 @@ static int dgram_ioctl(struct sock *sk, int cmd, int *karg) * of this packet since that is all * that will be read. */ - *karg = skb->len - ieee802154_hdr_length(skb); + *karg = skb->len; } spin_unlock_bh(&sk->sk_receive_queue.lock); return 0; -- 2.55.0.1082.g2b9226bbc0-goog