[PATCH 8/8] ext4: don't allow any modifications to an immutable file

Darrick J. Wong
2019-04-17T19:05:26Z

From: Darrick J. Wong <darrick.wong@oracle.com>

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>
---
fs/ext4/ioctl.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index bab3da4f1e0d..abf3b88d5af7 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)
{
@@ -322,6 +345,20 @@ static int ext4_ioctl_setflags(struct inode *inode,
goto flags_out;
}

+ /*
+ * 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);
@@ -751,7 +788,11 @@ 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;
@@ -1121,6 +1162,9 @@ 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;