From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B28C23546C1 for ; Sat, 1 Aug 2026 04:06:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785557204; cv=none; b=ZwAptYohyBzJrV0q413ledx8swjGw19PHP1zIN3zFaBAgsVGx5vBj3E4inqWAuZXuMMVPtmsIxSBl8+g+qkRFWfYPUVKCFDnbdAiBkBBlbHE+xGFGvqPeYpC8bfASTxnPRHNTDik5KkpatAa5IyO3rJAqtXfRWEkGrTcrD1WthI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785557204; c=relaxed/simple; bh=UAy8NywxBufXtt+fL8NnTeaU8ZFQCJNMaqa8XalBBFQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ldnvJAW4GhA5Tbd7WwCcpbF1M04A0KWjaJwB4iTBvbNcaNcguKyN3qUZS3nM89pRvSAHdMEK1B/OVQX1Vz5LCO5n9hX6/cguxPwOgWYm9wyH2f5Le4dg94bNYtchYTt1InU2YP0BG52iLYs7dEylMQZF6/emCFifD33R7wEge8Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BaZ+I8dR; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BaZ+I8dR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 017B31F00AC4; Sat, 1 Aug 2026 04:06:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785557203; bh=UXS8psxrn2y2ifr+kCCRbzyp0+s8gXQ6esAdRmRZzT8=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=BaZ+I8dR3a0uWPHiCyZiql56IdFofcMiLeI3r52RYn2fiwM6HnsZ0Uq4/IL4GC7zj LAFcY4Ii+aUd4Z7qSrBzDTp+DMJBf5tJblqp1rneSAK93u9Qmjr3e5AgsNI0CB21Da EVUQrDK3hu6nr5ooDMcAERT4caYIOJT0Ac3FnSEdu5C6wNPWrpxLxybmwSYco/y0Kt mzzJZiycAW+FuagL92C0Qi6KplJfPmblhRZtOwe9nF9DWYTQxd4I7luHpo4NPOXqM+ UJYzywzApYlxscG/2YnzhVj6pGXz+khyy3uCD2oPO6M1nBAV0T+nOInBPJYQrXaFUC y2E/itE0R97Kg== Date: Sat, 1 Aug 2026 13:06:41 +0900 From: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= To: Bjorn Helgaas Cc: Bjorn Helgaas , Manivannan Sadhasivam , Lorenzo Pieralisi , Kees Cook , linux-pci@vger.kernel.org Subject: Re: [PATCH] PCI/proc: Use file_ns_capable() when checking config space read access Message-ID: <20260801040625.GD3183355@rocinante> References: <20260720204145.1500105-1-kwilczynski@kernel.org> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260720204145.1500105-1-kwilczynski@kernel.org> Hello, > proc_bus_pci_read() decides how much of the config space is readable > based on capable(CAP_SYS_ADMIN), which checks the credentials of the > task calling read(), not the credentials of the process that opened > the file. > > The sysfs equivalent, pci_read_config(), has checked the credentials > of the opening process since commit de139a339395 ("pci: check caps > from sysfs file open to read device dependent config space"), so a > privileged process can open the config space file and pass the file > descriptor to an unprivileged process (for example, a process running > a KVM guest with an assigned device), which can then read the entire > config space. The check was subsequently routed through the LSM > framework in commit 47970b1b2aa6 ("pci: use security_capable() when > checking capablities during config space read") and converted to the > dedicated helper in commit ab0fa82b2df9 ("pci-sysfs: use proper file > capability helper function"). > > Thus, the two interfaces check the same capability against different > credentials. Checking the credentials of the task calling read() > makes the outcome depend on who reads rather than who opened, so the > restriction is bypassed whenever a more privileged process reads > through the descriptor. Checking the credentials recorded in > file->f_cred settles the decision at open() time and ties it to the > file, where it cannot change with the caller. > > Therefore, use file_ns_capable() to check CAP_SYS_ADMIN against the > credentials in effect when the file was opened, bringing the procfs > interface in line with the sysfs behaviour. > > As a result, a file descriptor opened by a privileged process and > passed to an unprivileged one now allows the entire config space to > be read through procfs, matching sysfs. Applied to the procfs branch. Thank you! Krzysztof