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Thu, 05 Nov 2026 07:17:53 -0800 (PST) Received: from toxicpanda.com ([153.61.196.253]) by smtp.gmail.com with ESMTPSA id ada2fe7eead31-7d26fe8f991sm4364149137.9.2026.11.05.07.17.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 07:17:53 -0800 (PST) From: Josef Bacik Date: Thu, 05 Nov 2026 15:02:40 +0000 Subject: [PATCH RFC v3 48/90] fs: refuse a task of a cell a new mount namespace X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261105-b4-cells-v3-48-bc9095937a84@toxicpanda.com> References: <20261105-b4-cells-v3-0-bc9095937a84@toxicpanda.com> In-Reply-To: <20261105-b4-cells-v3-0-bc9095937a84@toxicpanda.com> To: Christian Brauner , James Bottomley , Andrew Halaney , Jeremy Bingham , Tahera Fahimi , Serge Hallyn Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Josef Bacik X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openssh-sha256; t=1793890934; l=1326; i=josef@toxicpanda.com; h=from:subject:message-id; bh=nOXPHVO0v3hT1W2sHrZgWd3DNxkisQUAUu39TRuJmkY=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgUBr36M/n0nWN0DNbnxwzIiCZez6MG JiruuNaSCI/zXsAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QP9wmFv79GmH7EDKeFr9zp93V2hE/JATKfuBmIF+AlYfCq6/zq/mCDJAA5ZbBuYaoibPpl4dLA/ r4dWY2nDD2wc= X-Developer-Key: i=josef@toxicpanda.com; a=openssh; fpr=SHA256:C8kOX2QUJCMqnCX+KEeoqRAjLo9L+ELOSH2NSAJHqGA OPEN_TREE_NAMESPACE and FSMOUNT_NAMESPACE create a mount namespace without going through unshare(). A task of a cell could not enter such a namespace, but it should not be able to create namespaces in the first place. Refuse both flags for a task of a cell. Signed-off-by: Josef Bacik --- fs/namespace.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 7298b589e10e..30167f8863bf 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3353,6 +3353,9 @@ static struct file *vfs_open_tree(int dfd, const char __user *filename, unsigned * just care about being privileged over our current user namespace. * The new mount namespace will be owned by it. */ + if ((flags & OPEN_TREE_NAMESPACE) && current_cell()) + return ERR_PTR(-EPERM); + if ((flags & OPEN_TREE_NAMESPACE) && !ns_capable(current_user_ns(), CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); @@ -4622,6 +4625,9 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, if ((flags & ~(FSMOUNT_CLOEXEC | FSMOUNT_NAMESPACE)) != 0) return -EINVAL; + if ((flags & FSMOUNT_NAMESPACE) && current_cell()) + return -EPERM; + if ((flags & FSMOUNT_NAMESPACE) && !ns_capable(current_user_ns(), CAP_SYS_ADMIN)) return -EPERM; -- 2.55.0