The patch below does not apply to the 4.9-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 2e53840362771c73eb0a5ff71611507e64e8eecd Mon Sep 17 00:00:00 2001

From: "Darrick J. Wong" darrick.wong@oracle.com Date: Sun, 9 Jun 2019 21:41:41 -0400 Subject: [PATCH] ext4: don't allow any modifications to an immutable file

Don't allow any modifications to a file that's marked immutable, which means that we have to flush all the writable pages to make the readonly and we have to check the setattr/setflags parameters more closely.

Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@kernel.org

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c index e486e49b31ed..7af835ac8d23 100644 --- a/fs/ext4/ioctl.c +++ b/fs/ext4/ioctl.c @@ -269,6 +269,29 @@ static int uuid_is_zero(__u8 u[16]) } #endif

+/* + * If immutable is set and we are not clearing it, we're not allowed to change + * anything else in the inode. Don't error out if we're only trying to set + * immutable on an immutable file. + */ +static int ext4_ioctl_check_immutable(struct inode *inode, __u32 new_projid, + unsigned int flags) +{ + struct ext4_inode_info *ei = EXT4_I(inode); + unsigned int oldflags = ei->i_flags; + + if (!(oldflags & EXT4_IMMUTABLE_FL) || !(flags & EXT4_IMMUTABLE_FL)) + return 0; + + if ((oldflags & ~EXT4_IMMUTABLE_FL) != (flags & ~EXT4_IMMUTABLE_FL)) + return -EPERM; + if (ext4_has_feature_project(inode->i_sb) && + __kprojid_val(ei->i_projid) != new_projid) + return -EPERM; + + return 0; +} + static int ext4_ioctl_setflags(struct inode *inode, unsigned int flags) { @@ -340,6 +363,20 @@ static int ext4_ioctl_setflags(struct inode *inode, } }

+ /* + * Wait for all pending directio and then flush all the dirty pages + * for this file. The flush marks all the pages readonly, so any + * subsequent attempt to write to the file (particularly mmap pages) + * will come through the filesystem and fail. + */ + if (S_ISREG(inode->i_mode) && !IS_IMMUTABLE(inode) && + (flags & EXT4_IMMUTABLE_FL)) { + inode_dio_wait(inode); + err = filemap_write_and_wait(inode->i_mapping); + if (err) + goto flags_out; + } + handle = ext4_journal_start(inode, EXT4_HT_INODE, 1); if (IS_ERR(handle)) { err = PTR_ERR(handle); @@ -769,7 +806,11 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) return err;

inode_lock(inode); - err = ext4_ioctl_setflags(inode, flags); + err = ext4_ioctl_check_immutable(inode, + from_kprojid(&init_user_ns, ei->i_projid), + flags); + if (!err) + err = ext4_ioctl_setflags(inode, flags); inode_unlock(inode); mnt_drop_write_file(filp); return err; @@ -1139,6 +1180,9 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) goto out; flags = (ei->i_flags & ~EXT4_FL_XFLAG_VISIBLE) | (flags & EXT4_FL_XFLAG_VISIBLE); + err = ext4_ioctl_check_immutable(inode, fa.fsx_projid, flags); + if (err) + goto out; err = ext4_ioctl_setflags(inode, flags); if (err) goto out;