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[2a02:3100:ae86:1b01:80e2:8851:4221:68d8]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482fbb33070sm12540616f8f.36.2026.08.29.14.33.03 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 29 Aug 2026 14:33:03 -0700 (PDT) From: Karl Mehltretter To: selinux@vger.kernel.org Cc: Karl Mehltretter , Paul Moore , Stephen Smalley , Ondrej Mosnacek , Miklos Szeredi , Amir Goldstein , Christian Brauner , Baokun Li , linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH v3 0/2] selinux: fix nested backing-file mprotect checks Date: Sat, 29 Aug 2026 23:32:54 +0200 Message-Id: <20260829213256.51527-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-unionfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Patch 1 preserves the top-level user file SID across nested backing files. Patch 2 preserves and rechecks each intermediate path, mounter SID, and file-description SID during mprotect(), including execmod checks. The series is based on cf72cbb39da8, which contains commit f2381b546e7e ("fs: fix user path of nested backing files"). Neither patch needs that fix to apply or build, but without it the top-level check still resolves to the intermediate inode. It is already marked for stable. The intermediate list is allocated only for nested backing files. It is captured at backing-file allocation time and remains immutable afterwards. Capturing it in the mmap hook would require synchronization between concurrent mappings of the same file. Tested on arm64 QEMU with a small BusyBox initramfs, SELinux enforcing, and two nested overlayfs mounts. The original SID propagation test passes. Direct mmap(PROT_EXEC) and mmap(PROT_NONE) followed by mprotect(PROT_EXEC) are both denied against the intermediate inode when that permission is omitted. /proc/self/maps reports the top-level path. Changes in v3: - Add the intermediate-mounter fix as patch 2. - Allocate intermediate state only for nested backing files. - Rebase and retest on mainline containing f2381b546e7e. - Document the BusyBox test environment. Changes in v2: - Add selinux_file_user_sid() instead of open-coding the lookup (Amir). v2: https://lore.kernel.org/selinux/20260820175832.44512-1-kmehltretter@gmail.com/ Karl Mehltretter (2): selinux: preserve user SID across nested backing files selinux: recheck intermediate backing files on mprotect security/selinux/hooks.c | 150 ++++++++++++++++++++++++++---- security/selinux/include/objsec.h | 10 +- 2 files changed, 142 insertions(+), 18 deletions(-) base-commit: cf72cbb39da84b6f02f90c07f33b102fc10b16f0 -- 2.53.0