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([2a01:4b00:bf28:2e00:ff96:2dac:a39:3e10]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39efa433191sm19319164f8f.31.2025.04.23.07.48.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Apr 2025 07:48:53 -0700 (PDT) Message-ID: Date: Wed, 23 Apr 2025 15:48:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] maccess: fix strncpy_from_user_nofault empty string handling To: Steven Rostedt Cc: Andrew Morton , linux-mm@kvack.org, mhiramat@kernel.org, andrii@kernel.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, Mykyta Yatsenko , Kees Cook References: <20250422131449.57177-1-mykyta.yatsenko5@gmail.com> <20250422172011.feb243d2f7478c0e7109b74c@linux-foundation.org> <08e3ec4c-4401-403e-9d81-5ee0abebba5c@gmail.com> <20250423095941.1cab813f@gandalf.local.home> Content-Language: en-US From: Mykyta Yatsenko In-Reply-To: <20250423095941.1cab813f@gandalf.local.home> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 487D9120013 X-Rspamd-Server: rspam04 X-Stat-Signature: e7jnxpazmcuzbssaxngghwnrkda6j18m X-HE-Tag: 1745419735-526809 X-HE-Meta: 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 SfXcJ+k3 YyfiS0jbF1pdYOD7Wl/UShji5Avnja0XpEjJhNI6S7scfQ3NkbyIgIN+tDL6eFMj9XeQva/hfs6IPJX+hG5c4HmEd3hsWbxgf8MOjrW220QjHdxjMBZEMMCH9Ltgg5dPvbhaHDUMXboA8OLexgeh2TdEbFFGizy+j4tmQ4QOK/W92deiBObIAuh6C3AbRzNu3jcn4X7hR7cn1f0J4GKHt5/D3BgYX0z3CDHIIYsNIGIpKMgfjKNzKGD7bsoBeausCdJ4/QdIKWtLmLPqaQxqR/CNV/l3xyXEPRwoeN4ayn+nvUGWWIHk2QBAd8mVnVS4LZd956dlgec035P8I3dqemfj0znjOBOMf2fM5aoB4XChvPqWrotlCfYOntReWkmf3Wb3T9ATTcjrwhP3ul0A9aGBQcxgd+WAN9I0PS3Vmb6+h02YWvD1S9SEORVcYkMsxrdOebjf+FfW1WM2+PiL8jvEhjKabt/tuD3geJSa2dMXtY/NvZ25VGIQ8LZfjFXPXPsgkm7lkUD/VKsmzhxA6obnnnQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/23/25 14:59, Steven Rostedt wrote: > On Wed, 23 Apr 2025 12:37:46 +0100 > Mykyta Yatsenko wrote: > >>> Does this fix any known runtime issue? If so, please fully describe this? >> Not that I'm aware of. The issue could be found when trying to copy empty >> user space string in BPF program (and relying on return value).There are >> some usage of >> `strncpy_from_user_nofault` in tracing subsystem, but I'm not sure how to >> hit those code paths. >>> > Although your patch found a bug in the tracing subsystem, this wasn't the > cause. It only cared if the read faulted or not. It was incorrectly > checking for zero as non fault when in reality, it needed to check >= 0. > > With that fixed, it should work the same with or without this patch. > > -- Steve Sure, I had in mind usages from trace_probe_kernel.h, namely fetch_store_string_user, fetch_store_string, having a second look, it appears these only used in trace_events_synth.c, and we are good there.