From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 133553090D9; Thu, 2 Apr 2026 13:30:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775136613; cv=none; b=rxs/u45LoCgKdwYT1gnL+CBpG7+VwWsCMYIj/ZiB1U1Svh+BUw/tkfZ2YKDpTYF23axcOsq0xDWTs99DtIYYL/mgLcW5Ksb9BcBg14ngg5kojGD4dyXTcSjwzMcL3C5YweOJwqmYYPIWSgfnhgyKTt+W7fIdEBe1Cb9TBAve4wQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775136613; c=relaxed/simple; bh=5vx+5BBjttOguBfqndjxofXdmyNOKnD9V2uUeBtIGew=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SW9PAjaBJLu/qXC45pi9KLhYHl6+QjqFWTpj2GQs8xlCuafThSZ71SUs0qrCaJc3PF03ghIUBvg60iVwQbi6O/1yAEfcrd79S3lF4u0JMmmxDXYQ2wQg+SRrqYbNt7xYsJJ/S6euHtZNkonuqyvQoK5ATn2PmK9uq/sWGdtp7lc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tvgL1VEm; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="tvgL1VEm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E6F1DC116C6; Thu, 2 Apr 2026 13:30:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775136612; bh=5vx+5BBjttOguBfqndjxofXdmyNOKnD9V2uUeBtIGew=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tvgL1VEmtUAilcFdK3h4y2NVdidXm6hV62quZe+1aJHOBMAsdnuwXSXnhY1/Y/hdP MDNBq7/I7ESXw3HD/ZVS83PXDvs60+g9f7dT2xL+mcWLpvB0YqnILKOMSIEUwRBUE9 3lXaNN59TQpkDt2bBEyWDYHiTpVAjTB/noVUdF5RKCeBjpXPNWb2TDJv/D/rHPPqLJ oYg8fRiugwstTE+ciP/wayxeaLjhSVsryJ60Seje+gl6xMajJnDcWy52Ky9j0URk7n NSrbbccVaRFZVJQ9N4zYXcxxOpBYQ3t7kC04WQ5DakiFGKaFEqnedOwvY1ShXX1e4F 170faYhAYoxtQ== Message-ID: <6444fb38-cc33-4402-9fed-11e9938d131f@kernel.org> Date: Thu, 2 Apr 2026 15:30:07 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] prctl: require checkpoint_restore_ns_capable for PR_SET_MM_MAP To: Qi Tang , Andrew Morton Cc: Cyrill Gorcunov , Lorenzo Stoakes , Oleg Nesterov , linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260402111332.55957-1-tpluszz77@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/2/26 13:13, Qi Tang wrote: > prctl_set_mm_map() allows modifying all mm_struct boundaries and > the saved auxv vector. The individual field path (PR_SET_MM_START_CODE > etc.) correctly requires CAP_SYS_RESOURCE, but the PR_SET_MM_MAP path > dispatches before this check and has no capability requirement of its > own when exe_fd is -1. > > This means any unprivileged user on a CONFIG_CHECKPOINT_RESTORE kernel > (nearly all distros) can rewrite mm boundaries including start_brk, brk, > arg_start/end, env_start/end and saved_auxv. Consequences include: > > - SELinux PROCESS__EXECHEAP bypass via start_brk manipulation > - procfs info disclosure by pointing arg/env ranges at other memory > - auxv poisoning (AT_SYSINFO_EHDR, AT_BASE, AT_ENTRY) > > The original commit f606b77f1a9e ("prctl: PR_SET_MM -- introduce > PR_SET_MM_MAP operation") states "we require the caller to be at least > user-namespace root user", but this was never enforced in the code. That is taken out of contex, no? "Still note that updating exe-file link now doesn't require sys-resource capability anymore, ... Still we require the caller to be at least user-namespace root user." That check was added in prctl_set_mm_map()->validate_prctl_map() in the original patch: + /* + * Finally, make sure the caller has the rights to + * change /proc/pid/exe link: only local root should + * be allowed to. + */ + if (prctl_map->exe_fd != (u32)-1) { + struct user_namespace *ns = current_user_ns(); + const struct cred *cred = current_cred(); + + if (!uid_eq(cred->uid, make_kuid(ns, 0)) || + !gid_eq(cred->gid, make_kgid(ns, 0))) + goto out; + } -- Cheers, David