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Thu, 05 Nov 2026 06:58:08 -0800 (PST) Received: from toxicpanda.com ([153.61.196.251]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4acea680cacsm4490943fac.16.2026.11.05.06.58.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 06:58:07 -0800 (PST) From: Josef Bacik Date: Thu, 05 Nov 2026 14:56:58 +0000 Subject: [PATCH RFC v3 07/90] ucount: count the id blocks a user holds 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-v3-7-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=1793890669; l=1206; i=josef@toxicpanda.com; h=from:subject:message-id; bh=nNOYagXPS7UuclEa6CcqzF+lG9K1DgR6fFtMR2Grrjc=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgUBr36M/n0nWN0DNbnxwzIiCZez6MG JiruuNaSCI/zXsAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QIMu8+xlcTKBuamFsS4d1TuvaQKBaizx5lSbbA0HZfVJWo4o7PZbAa8Z4P+CWt1buiOR2uGpoPQ UEHhTUD2aMgk= X-Developer-Key: i=josef@toxicpanda.com; a=openssh; fpr=SHA256:C8kOX2QUJCMqnCX+KEeoqRAjLo9L+ELOSH2NSAJHqGA A block of ids gives access to nothing, so taking one requires no privilege. But the number of blocks is limited. Add a ucount, user.max_cell_id_blocks, so that a single user cannot use up the window. Signed-off-by: Josef Bacik --- include/linux/user_namespace.h | 3 +++ kernel/ucount.c | 3 +++ 2 files changed, 6 insertions(+) diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 5c8cf31ab9d4..f0b0fe12c2fd 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -61,6 +61,9 @@ enum ucount_type { #endif #if IS_ENABLED(CONFIG_BINFMT_MISC) UCOUNT_BINFMT_MISC_INTERPRETERS, +#endif +#ifdef CONFIG_CELLS + UCOUNT_CELL_ID_BLOCKS, #endif UCOUNT_COUNTS, }; diff --git a/kernel/ucount.c b/kernel/ucount.c index 94b70502dc9d..7eab985121f6 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -93,6 +93,9 @@ static const struct ctl_table user_table[] = { #if IS_ENABLED(CONFIG_BINFMT_MISC) UCOUNT_ENTRY("max_binfmt_misc_interpreters"), #endif +#ifdef CONFIG_CELLS + UCOUNT_ENTRY("max_cell_id_blocks"), +#endif }; #endif /* CONFIG_SYSCTL */ -- 2.55.0