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[34.16.134.225]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2e4c2a7e76csm4075525ad.31.2026.10.02.10.17.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Oct 2026 10:17:10 -0700 (PDT) From: Daeho Jeong To: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com Cc: Daeho Jeong Subject: [PATCH] f2fs: disallow mmap write and data-modifying fallocate on atomic files Date: Fri, 2 Oct 2026 17:17:04 +0000 Message-ID: <20261002171704.3652570-1-daeho43@gmail.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Daeho Jeong Stores through a shared writable mapping and fallocate with FALLOC_FL_PUNCH_HOLE, FALLOC_FL_ZERO_RANGE, FALLOC_FL_COLLAPSE_RANGE or FALLOC_FL_INSERT_RANGE do not go through ->write_begin, so they bypass the COW inode and modify the original inode directly. Reject them while the file is in atomic write mode, as fallocate already does for pinned and compressed files. A write fault gets SIGBUS and fallocate gets -EOPNOTSUPP. fallocate without these flags only preallocates blocks and stays allowed. Fixes: 3db1de0e582c ("f2fs: change the current atomic write way") Signed-off-by: Daeho Jeong --- fs/f2fs/file.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index ef4d218e694..56c686b8580 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -140,6 +140,10 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf) return VM_FAULT_SIGBUS; } + /* mmap stores bypass the COW inode and would break atomicity */ + if (f2fs_is_atomic_file(inode)) + return VM_FAULT_SIGBUS; + if (is_inode_flag_set(inode, FI_COMPRESS_RELEASED)) { err = -EIO; goto out; @@ -2113,9 +2117,11 @@ static long f2fs_fallocate(struct file *file, int mode, /* * Pinned file should not support partial truncation since the block - * can be used by applications. + * can be used by applications. Atomic files should not either, since + * these modify the original inode directly and break atomicity. */ - if ((f2fs_compressed_file(inode) || f2fs_is_pinned_file(inode)) && + if ((f2fs_compressed_file(inode) || f2fs_is_pinned_file(inode) || + f2fs_is_atomic_file(inode)) && (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE | FALLOC_FL_INSERT_RANGE))) { ret = -EOPNOTSUPP; -- 2.56.0.rc1.315.gc6ed9934b7-goog