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Sat, 06 Dec 2025 20:15:46 -0800 (PST) From: Dharanitharan R To: syzbot+5dd615f890ddada54057@syzkaller.appspotmail.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Dharanitharan R Subject: [PATCH] net: atm: lec: add pre_send validation to avoid uninitialized Date: Sun, 7 Dec 2025 04:14:53 +0000 Message-ID: <20251207041453.8302-1-dharanitharan725@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <202511281159.5dd615f890ddada54057@syzkaller.appspotmail.com> References: <202511281159.5dd615f890ddada54057@syzkaller.appspotmail.com> 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,=20 .send =3D lec_atm_send }; =20 --=20 2.43.0