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Thu, 12 Nov 2026 13:43:20 -0800 (PST) Received: from localhost.localdomain ([98.148.34.5]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-37956bad134sm1194466eec.27.2026.11.12.13.43.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Nov 2026 13:43:19 -0800 (PST) From: Hungyu Lin To: jaegeuk@kernel.org, chao@kernel.org Cc: daehojeong@google.com, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, dennylin0707@gmail.com Subject: [PATCH v2 2/4] f2fs: require write permission for F2FS_IOC_RELEASE_COMPRESS_BLOCKS Date: Thu, 12 Nov 2026 21:43:01 +0000 Message-ID: <20261112214303.16198-3-dennylin0707@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261112214303.16198-1-dennylin0707@gmail.com> References: <20261112214303.16198-1-dennylin0707@gmail.com> 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-Transfer-Encoding: 8bit F2FS_IOC_RELEASE_COMPRESS_BLOCKS does not check who the caller is, so any user who can open a compressed file, even read-only, can release its compressed blocks. After that, writes to the file fail with -EPERM until the blocks are reserved again or the file is truncated to zero. Require write permission on the inode. inode_permission() does not depend on how the file was opened, so a caller with write permission can still release the blocks through a read-only file descriptor, as f2fs_io and Android do. Fixes: ef8d563f184e ("f2fs: introduce F2FS_IOC_RELEASE_COMPRESS_BLOCKS") Suggested-by: Chao Yu Cc: stable@vger.kernel.org Signed-off-by: Hungyu Lin --- fs/f2fs/file.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index cfd24a5fa271..93f892b11915 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -4238,6 +4238,9 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg) if (f2fs_readonly(sbi->sb)) return -EROFS; + if (inode_permission(file_mnt_idmap(filp), inode, MAY_WRITE)) + return -EACCES; + ret = mnt_want_write_file(filp); if (ret) return ret; -- 2.43.0