The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e0fcd01510ad025c9bbce704c5c2579294056141 Mon Sep 17 00:00:00 2001

From: Chao Yu chao@kernel.org Date: Sat, 26 Dec 2020 18:07:01 +0800 Subject: [PATCH] f2fs: enforce the immutable flag on open files

This patch ports commit 02b016ca7f99 ("ext4: enforce the immutable flag on open files") to f2fs.

According to the chattr man page, "a file with the 'i' attribute cannot be modified..." Historically, this was only enforced when the file was opened, per the rest of the description, "... and the file can not be opened in write mode".

There is general agreement that we should standardize all file systems to prevent modifications even for files that were opened at the time the immutable flag is set. Eventually, a change to enforce this at the VFS layer should be landing in mainline.

Cc: stable@kernel.org Signed-off-by: Chao Yu yuchao0@huawei.com Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index 2ddc4baaf173..d57b54643918 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -60,6 +60,9 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf) bool need_alloc = true; int err = 0;

+ if (unlikely(IS_IMMUTABLE(inode))) + return VM_FAULT_SIGBUS; + if (unlikely(f2fs_cp_error(sbi))) { err = -EIO; goto err; @@ -865,6 +868,14 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr) if (unlikely(f2fs_cp_error(F2FS_I_SB(inode)))) return -EIO;

+ if (unlikely(IS_IMMUTABLE(inode))) + return -EPERM; + + if (unlikely(IS_APPEND(inode) && + (attr->ia_valid & (ATTR_MODE | ATTR_UID | + ATTR_GID | ATTR_TIMES_SET)))) + return -EPERM; + if ((attr->ia_valid & ATTR_SIZE) && !f2fs_is_compress_backend_ready(inode)) return -EOPNOTSUPP; @@ -4351,6 +4362,11 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from) inode_lock(inode); }

+ if (unlikely(IS_IMMUTABLE(inode))) { + ret = -EPERM; + goto unlock; + } + ret = generic_write_checks(iocb, from); if (ret > 0) { bool preallocated = false; @@ -4415,6 +4431,7 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from) if (ret > 0) f2fs_update_iostat(F2FS_I_SB(inode), APP_WRITE_IO, ret); } +unlock: inode_unlock(inode); out: trace_f2fs_file_write_iter(inode, iocb->ki_pos,