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[209.85.218.52]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-aa5996c1383sm301620066b.40.2024.11.30.10.08.59 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 30 Nov 2024 10:08:59 -0800 (PST) Received: by mail-ej1-f52.google.com with SMTP id a640c23a62f3a-a9f1d76dab1so522474766b.0 for ; Sat, 30 Nov 2024 10:08:59 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCXKMJHdK/8zN6CCzMqPAdhYYW5EwI5NyAaE+F2jaTD5J7jDKd0EMP951m22WedCdPLW6vldQS0Daw==@kvack.org X-Received: by 2002:a17:906:1ba9:b0:aa5:cec:2785 with SMTP id a640c23a62f3a-aa580f50e22mr1700257566b.25.1732989774448; Sat, 30 Nov 2024 10:02:54 -0800 (PST) MIME-Version: 1.0 References: <20241130045437.work.390-kees@kernel.org> <20241130-ohnegleichen-unweigerlich-ce3b8af0fa45@brauner> In-Reply-To: <20241130-ohnegleichen-unweigerlich-ce3b8af0fa45@brauner> From: Linus Torvalds Date: Sat, 30 Nov 2024 10:02:38 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case To: Christian Brauner Cc: Kees Cook , Al Viro , =?UTF-8?Q?Zbigniew_J=C4=99drzejewski=2DSzmek?= , Tycho Andersen , Aleksa Sarai , Eric Biederman , Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 7AA0B80018 X-Stat-Signature: te3bxpkaui8om35r9d3azxoukh8ctx3p X-Rspam-User: X-HE-Tag: 1732990123-20393 X-HE-Meta: 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 nazZYwzi 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 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 Sat, 30 Nov 2024 at 04:30, Christian Brauner wrote: > > What does the smp_load_acquire() pair with? I'm not sure we have them everywhere, but at least this one at dentry creation time. __d_alloc(): /* Make sure we always see the terminating NUL character */ smp_store_release(&dentry->d_name.name, dname); /* ^^^ */ so even at rename time, when we swap the d_name.name pointers (*without* using a store-release at that time), both of the dentry names had memory orderings before. That said, looking at swap_name() at the non-"swap just the pointers" case, there we do just "memcpy()" the name, and it would probably be good to update the target d_name.name with a smp_store_release. In practice, none of this ever matters. Anybody who uses the dentry name without locking either doesn't care enough (like comm[]) or will use the sequence number thing to serialize at a much higher level. So the smp_load_acquire() could probably be a READ_ONCE(), and nobody would ever see the difference. Linus