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Fri, 17 Apr 2026 09:41:59 +0000 (GMT) Received: from bblock by p1gen4-pw042f0m with local (Exim 4.99.1) (envelope-from ) id 1wDfi3-00000005wlO-33Rc; Fri, 17 Apr 2026 11:41:59 +0200 Date: Fri, 17 Apr 2026 11:41:59 +0200 From: Benjamin Block To: Pengpeng Hou Cc: Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thorsten Blum , Tigran Mkrtchyan , Kees Cook , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] s390/debug: reject zero-length input before trimming a newline Message-ID: <20260417094159.GD28991@p1gen4-pw042f0m> References: <20260417073530.96002-1-pengpeng@iscas.ac.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260417073530.96002-1-pengpeng@iscas.ac.cn> Sender: Benjamin Block X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 9pSW9i038oPHejctRDWOpCY2z8ZNxhbO X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDE3MDA5MiBTYWx0ZWRfXzrxbAShCDafk 6VdBXJES4/8i3k8d2lXD4hvVdGuKdzuOZJJG3+oxou8vPodk6cyYVkDWBHx/RxWwI0ZAFntHocQ IqoXH5TAliUetPLsbcY08FFGAASRLu4BTxiU8zhg80jbRajHRE8Tb+VLjHiK6TFwmCcHYcMAOpM eyPEPe/jqLWdwEQnWceqSk3bw8DcRV3LKLu1Z+5iFxAiFQAL6qlDsWzPVLQfsaRomsUlG2Y7nMi oZ3dJA22/T+vmV8KF32imrYopkitCA8znw4oIGjiUfcsPPzE95dP7dpBBT9pnzbkEjMY/61d9Vo yfn4/LjCrNNk5LamEPKSMMd1FAQNB3ycuOENVS9rvy933OAQ8Ms7OJPurnmifhqXiFP30DSaCtR sdVVY5Nt77IlwVNep+tG7QURKJiQhlLSfEX36fOb46BYHROewRK74yKx8I5QTfqmy4HpxXNaNwl tWoVe6P1S87x6H2HMjQ== X-Proofpoint-ORIG-GUID: 9pSW9i038oPHejctRDWOpCY2z8ZNxhbO X-Authority-Analysis: v=2.4 cv=W60IkxWk c=1 sm=1 tr=0 ts=69e2006c cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=8nJEP1OIZ-IA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=6aPio0FCpJ9vPV8vH-IA:9 a=3ZKOabzyN94A:10 a=wPNLvfGTeEIA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-16_04,2026-04-16_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1011 priorityscore=1501 spamscore=0 bulkscore=0 adultscore=0 phishscore=0 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604070000 definitions=main-2604170092 On Fri, Apr 17, 2026 at 03:35:30PM +0800, Pengpeng Hou wrote: > debug_get_user_string() duplicates the userspace buffer with > memdup_user_nul() and then unconditionally looks at buffer[user_len - 1] > to strip a trailing newline. > > A zero-length write reaches this helper unchanged, so the newline trim > reads before the start of the allocated buffer. > > Reject empty writes before accessing the last input byte. > > Fixes: 66a464dbc8e0 ("[PATCH] s390: debug feature changes") > There shouldn't be a blank line here. > Signed-off-by: Pengpeng Hou > --- > arch/s390/kernel/debug.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c > index 31430e9bcfdd..2612f634e826 100644 > --- a/arch/s390/kernel/debug.c > +++ b/arch/s390/kernel/debug.c > @@ -1414,6 +1414,9 @@ static inline char *debug_get_user_string(const char __user *user_buf, > { > char *buffer; > > + if (!user_len) > + return ERR_PTR(-EINVAL); > + > buffer = memdup_user_nul(user_buf, user_len); > if (IS_ERR(buffer)) > return buffer; Otherwise this looks good to me. Reviewed-by: Benjamin Block -- Best Regards, Benjamin Block / Linux on IBM Z Kernel Development IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy Vors. Aufs.-R.: Wolfgang Wendt / Geschäftsführung: David Faller Sitz der Ges.: Ehningen / Registergericht: AmtsG Stuttgart, HRB 243294