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Tue, 09 Dec 2025 19:56:37 -0800 (PST) Received: from localhost.localdomain ([38.134.139.135]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7e2ae03513fsm17408190b3a.43.2025.12.09.19.56.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Dec 2025 19:56:36 -0800 (PST) From: Dharanitharan R To: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, dharanitharan725@gmail.com Subject: [PATCH v3] net: atm: lec: add pre_send validation to avoid uninitialized Date: Wed, 10 Dec 2025 03:53:55 +0000 Message-ID: <20251210035354.17492-2-dharanitharan725@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" syzbot reported a KMSAN uninitialized-value crash caused by reading fields from struct atmlec_msg before validating that the skb contains enough linear data. A malformed short skb can cause lec_arp_update() and other handlers to access uninitialized memory. Add a pre_send() validator that ensures the message header and optional TLVs are fully present. This prevents all lec message types from reading beyond initialized skb data. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com Tested-by: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D5dd615f890ddada54057 Signed-off-by: Dharanitharan R --- net/atm/lec.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/net/atm/lec.c b/net/atm/lec.c index afb8d3eb2185..c893781a490a 100644 --- a/net/atm/lec.c +++ b/net/atm/lec.c @@ -489,8 +489,33 @@ static void lec_atm_close(struct atm_vcc *vcc) module_put(THIS_MODULE); } =20 +static int lec_atm_pre_send(struct atm_vcc *vcc, struct sk_buff *skb) +{ + struct atmlec_msg *mesg; + u32 sizeoftlvs; + unsigned int msg_size =3D sizeof(struct atmlec_msg); + + /* Must contain the base message */ + if (skb->len < msg_size) + return -EINVAL; + + /* Must have at least msg_size bytes in linear data */ + if (!pskb_may_pull(skb, msg_size)) + return -EINVAL; + + mesg =3D (struct atmlec_msg *)skb->data; + sizeoftlvs =3D mesg->sizeoftlvs; + + /* Validate TLVs if present */ + if (sizeoftlvs && !pskb_may_pull(skb, msg_size + sizeoftlvs)) + return -EINVAL; + + return 0; +} + static const struct atmdev_ops lecdev_ops =3D { .close =3D lec_atm_close, + .pre_send =3D lec_atm_pre_send, .send =3D lec_atm_send }; =20 --=20 2.43.0