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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8a86100263dsm35018497b3.35.2026.09.27.13.37.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Sep 2026 13:37:13 -0700 (PDT) Date: Sun, 27 Sep 2026 16:37:12 -0400 From: Willem de Bruijn To: =?UTF-8?B?SWxra2EgTGFwcGV0ZWzDpGluZW4=?= , Willem de Bruijn Cc: netdev@vger.kernel.org, security@kernel.org Message-ID: In-Reply-To: <20260925124829.6595-1-ilkka.lappetelainen@gmail.com> References: <20260925124829.6595-1-ilkka.lappetelainen@gmail.com> Subject: Re: [PATCH net] net/packet: prevent TX_RING byte count overflow Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Ilkka Lappetel=C3=A4inen wrote: > tpacket_snd() drains every SEND_REQUEST frame in a TX ring and adds > each valid packet length to the signed int len_sum. Userspace can > recycle completed frames concurrently, so a single blocking send call > is not bounded by the ring size. > = > After enough successful transmissions len_sum wraps into the negative > range. In particular, 65536 65535-byte frames followed by a 65007-byte > frame produce 0xfffffdef, or -EIOCBQUEUED. sock_sendmsg_nosec() treats > that as an impossible return and triggers a BUG. On systems configured > to panic on oops, a CAP_NET_RAW holder can panic the host kernel. > = > Stop before the next frame would make the byte count exceed INT_MAX. > The positive short count leaves that frame pending for a later send > call. > = > A two-thread TPACKET_V2 reproducer triggered the BUG on an arm64 build > of Linux 7.3-rc4. With this change, the same reproducer returned the > expected positive short count without an oops. > = > Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Ilkka Lappetel=C3=A4inen = Reviewed-by: Willem de Bruijn